((Title))



Exploring Structure-Property Relationships of Silver 4-(Phenylethynyl)pyridine Complexes-800108117840[a]J. V. Knichal, Dr W. J. Gee, Dr C. A. Cameron, Dr J. M. Skelton, Professor C. C. Wilson, Professor P. R. Raithby, Professor A. D. Burrows.Department of Chemistry, University of Bath,Claverton Down, Bath BA2 7AY (UK)E-mail: (A.D.B): a.d.burrows@bath.ac.uk, bath.ac.uk/chemistry/contacts/academics/andrew_burrows/[b]Dr K. J. Gagnon, Dr S. J. Teat.Station 11.3.1Advanced Light Source, Lawrence Berkeley National LaboratoryBerkeley, CA 94720 (USA)Supporting information for this article is given via a link at the end of the document.00[a]J. V. Knichal, Dr W. J. Gee, Dr C. A. Cameron, Dr J. M. Skelton, Professor C. C. Wilson, Professor P. R. Raithby, Professor A. D. Burrows.Department of Chemistry, University of Bath,Claverton Down, Bath BA2 7AY (UK)E-mail: (A.D.B): a.d.burrows@bath.ac.uk, bath.ac.uk/chemistry/contacts/academics/andrew_burrows/[b]Dr K. J. Gagnon, Dr S. J. Teat.Station 11.3.1Advanced Light Source, Lawrence Berkeley National LaboratoryBerkeley, CA 94720 (USA)Supporting information for this article is given via a link at the end of the document.Jane V. Knichal,[a] William J. Gee,[a] Christopher A. Cameron,[a] Jonathan M. Skelton,[a] Kevin J. Gagnon,[b] Simon J. Teat,[b] Chick C. Wilson,*[a] Paul R. Raithby,*[a] and Andrew D. Burrows*[a]Dedication ((optional))Abstract: Silver(I) salts demonstrate a strong preference for forming linear complexes when reacted with 4-(phenylethynyl)pyridine (pep). The packing of these complexes was found to be strongly influenced by the counter anions, namely PF6-, BF4-, NO2-, NO3-, MeCO2-, CF3CO2-, MeSO3-, Tos- and SCN-. This study evaluates a family of twelve solid-state structures that exhibit varying metal-to-ligand ratios, [Ag(pep)2][PF6]·MeCN (1a), [Ag(pep)2][PF6] (1b), [Ag(pep)2][BF4] (2), [Ag(pep)2][Ag(NO2)2] (3), [Ag(pep)2][NO3]·2H2O (4), [Ag(pep)2][Ag(NO3)2] (5), [Ag(pep)2(MeCO2)]·3H2O (6), [Ag(pep)2][CF3CO2] (7a, 7b), [Ag(pep)2][CF3SO3] (8), 2{[Ag(pep)2][Tos]}·pep (9), and [Ag(pep)(SCN)] (10). This family has enabled general trends and noteworthy packing-induced structure-property relationships to be elucidated. Highlights include two instances of single-crystal-to-single-crystals (SCSC) transformations, one of which occurs with a colour change. This change in crystal colour has been further explored using first-principles computational modelling.IntroductionImproved understanding of structure-property relationships is fundamental to controlling functionality, and a key step towards the development of next generation, ‘smart’ materials. Crystal engineering is a useful strategy to this end, whereby the prediction of molecular self-assembly at the atomic level is exploited to guide synthetic efforts towards a target architecture.[1] Extrapolation of well-engineered atomic-scale interactions can, through the repetition of a crystalline lattice, enable a bottom-up approach to building large and complex frameworks. The main obstacle to this strategy is predicting which molecular interactions will occur within a reaction mixture, in particular one containing complex mixtures of Lewis acids and bases. Similarly, predicting the outcome of competing molecular interactions can be extremely difficult for all but the simplest systems. Only by learning from relevant model systems can our current levels of understanding be improved. Our interest in this area has been focused on how weak, often overlooked, interactions, such as C-H···X hydrogen bonding, influence the self-assembly of coordination polymers.[2] Here we take this further, investigating the affinity of materials dominated by these interactions to undergoing single-crystal-to-single-crystal (SCSC) transformations. We approached this by focusing on silver complexes, which represent a challenging crystal engineering target owing to the flexible coordination sphere and variable coordination number of the metal.[3] However, the lability of Ag-ligand interactions, which are approximately equivalent in strength to a strong hydrogen bond,[3] ensure that weak interactions such as argentophilic Ag···Ag interactions, ?···? interactions and C-H···X (X = O, N, ?) interactions must play a prominent role in the resulting material’s self-assembly. Several studies have demonstrated the great relevance that silver complexes have to crystal engineering.[4] The model system we have chosen is based on the silver 4-(phenylethynyl)pyridine (pep) synthon. Variation of the counter anion (PF6-, BF4-, NO2-, NO3-, MeCO2-, CF3CO2-, MeSO3-, Tos- and SCN-) yields a family of materials that can be used to investigate trends and structure-property relationships. These counter-ions were chosen to include traditionally non-coordinating species, bridging ions and hydrogen bond donors/acceptors, and also variation in steric bulk and polarizability. Non-covalent interactions and anion templating are both well known for their ability to unexpectedly influence the outcome of framework architectures,[5] highlighting the need for further investigations to better allow their application in crystal engineering studies. The choice of pep as the ligand stemmed from our aim to generate linear complexes while maximizing the likelihood of weak interactions. The pep ligand coordinates through a pyridyl group, which inhibits metal bridging modes and thus aggregation. The central alkyne functionality can impart limited but demonstrable flexibility to the ligand, as highlighted by the recent synthesis of ?-conjugated spoked-wheel macrocycles.[6] This flexibility, by extension, is transferred to supramolecular packing arrangements. Only one well-characterized solid-state structure incorporating pep is known, from a study investigating the excited-state properties of ruthenium complexes.[7] An earlier study complementing this work explored the influence of the anion on a variety of silver aromatic chains, including 1,4-bis(4-pyridylethynyl)phenylene, an extended bidentate variant of pep.[8] The rich chemistry of silver 4,4’-bipyridine structures further conveys the complexity in the field of silver pyridyl species.[9] Because of this demonstrable complexity, this study will be limited to a single ligand, whose chemistry we aim to explore thoroughly. While the primary focus of this work is to improve crystal-engineering strategies involving weak interactions, complexes of silver have a variety of known uses, including medicinally for anti-cancer[10] and anti-microbial activity,[11] and within luminescent devices.[12] Similarly, there are several studies exploring other aspects of silver complexes within the field of crystal engineering,[13] and in the use of silver-containing linkers in coordination-polymer synthesis.[14] Our studies have identified a number of single-crystal-to-single-crystal (SCSC) transformations, which complement our past experiences exploring other systems dominated by weak, second coordination sphere bonds in the solid state which also exhibit such transformations.[15]Results and DiscussionThis study takes advantage of the known preference of silver to form linear coordination complexes with pyridyl donors[7-9], in this instance using the ligand 4-(phenylethynyl)pyridine (pep). The choice of pep was made owing to its optimal combination of a singular coordination region, linear shape, and flexible alkyne spacer, and to promote formation of weak interligand ?···? interactions. With continuity provided by the silver pep synthon, variation of the silver counter anion provides a way of influencing the weak non-coordination interactions that control the solid-state packing. In so doing, variation of the anion allows structure-property relationships to be explored. Ultimately, Table 1. Crystallographic Data for coordination polymers 1-10.1a1b2345formulaC56H42Ag2F12N6P2C26H18AgF6N2PC26H18AgBF4N2C26H18Ag2N4O4C26H22Ag1N3O5C26H18Ag2N4O6formula weight1304.63611.26553.10666.18564.35698.18wavelength, ?0.71073 0.710730.953700.710730.710730.71073crystal systemTriclinicTriclinicTriclinicTriclinicOrthorhombicMonoclinicspace groupP1 QUOTE P1P1P1 QUOTE P n a 21P 21a, ?9.6598(5)10.3864(7)9.7333(4)9.1122(9)11.0778(4)10.0155(3)b, ?10.4506(5)10.5527(8)10.4298(5)9.2733(9)29.7697(13)7.5869(2)c, ?26.8570(15)11.7212(9)11.4370(5)15.8574(16)7.5926(3)16.7367(5)α, °83.490(4)104.522(6)101.835(2)75.376(8)9090β, °79.690(5)99.244(6)93.615(2)73.607(9)90100.355(3)γ, °89.998(4)92.935(6)99.976(2)75.656(8)9090V, ?2649.7(2)1221.85(16)1113.31(9)1221.1(2)2503.91(17)1251.05(6)Z222242ρcalc, g/cm31.6351.6611.6501.8071.4971.853μ, mm-10.8870.9542.1911.6320.8461.615reflections measured2502910447194951007075645797unique reflections1224256266779559143954492no. observed (I > 2σ(I))462044416055289938184187Final R indexes (I ≥ 2σ(I))0.09460.16200.04890.07370.02610.05730.05760.06670.04110.06930.03160.0570Final R indexes [all data]0.22360.23050.06980.08290.03240.05930.13850.08620.04990.07170.03530.0595Flack parameter0.05(3)GOOF1.0151.0521.1220.9910.9241.010Temp, K150(1)150(2)100(1)150(1)150(1)150(1)67a7b8910formulaC28H21AgN2O2C56H36Ag2F6N4O4C56H36Ag2F6N4O4C27H18AgF3N2O3SC145H108Ag4N9O12S4C14H9AgN2Sformula weight525.341158.631158.63615.362728.12345.16wavelength, ?0.710730.953700.774901.541840.710730.95370crystal systemOrthorhombicMonoclinicMonoclinicMonoclinicMonoclinicMonoclinicspace groupP n a 21P 21/cC 2/cP 21C 2/cP 21a, ?11.1164(6)8.4508(4)19.3008(10)10.12120(10)31.4069(10)5.9402(2)b, ?30.4072(19)29.2580(12)9.5411(5)7.62970(10)7.0972(2)7.6749(4)c, ?7.5811(2)9.7107(4)26.0553(15)16.93930(10)28.8675(10)14.3366(6)α, °909090909090β, °9091.682(2)110.332(3)107.2340(10)111.174(4)96.730(2)γ, °909090909090V, ?2562.6(2)2399.97(18)4499.2(4)1249.35(2)6000.2(4)649.11(5)Z444222ρcalc, g/cm31.451 1.6031.7101.6361.5101.766μ, mm-10.8862.0431.1977.7420.7823.710reflections measured87353222733721337242325212054unique reflections449249164891470253064742no. observed (I > 2σ(I))399843044557467739734063Final R indexes (I ≥ 2σ(I))0.04650.11860.02770.05620.03550.08140.02190.06420.04280.11960.02930.0530Final R indexes [all data]0.05420.12550.03510.05830.04050.08410.02200.06430.06190.14080.03990.0557Flack parameter-0.015(6)0.17(2)GOOF0.8541.1211.0680.4141.1251.002Temp, K150(2)100(1)100(1)150(1)150(2)100(1)twelve solid-state crystalline species (1-10) were isolated and characterized for this study. In two instances (1a-b and 7a-b), crystals were obtained by SCSC transformations between the pairs of structures. Crystallographic data for all twelve compounds used in this study are summarized in Table 1.Identifying definitive covalent Ag-X (X = N, O) bond lengths within the literature proved to be surprisingly challenging, as summarized in a recent study of silver O-donor solvates.[16] Based on this previous study we chose 2.54 ? as the interatomic limit of a covalent Ag-X interaction. Similarly, a bond length of 2.53 ? was experimentally determined as the point of dissociation for a covalent Ag-Ag interaction,[17] which is in fair agreement with the value of 2.60 ? determined by a subsequent computational study,[18] although considerably shorter than a number early cited examples that range from 2.76 to 3.17 ?.[19] The Ag-S bond contains considerably more ionic than covalent character,[17] and hence labelling such bonds as covalent can be misleading. Although computational studies quote Ag-S bond lengths ranging from 3.01 ? to 3.40 ?,[17,18] this study makes use of the shorter distance as the limit of covalent bonding. Interactions beyond these covalent-bonding distances but within the sum of the van der Waals radii of the metal and coordinating atom are termed second coordination sphere bonds and are known to play important roles owing to the prevalence of weak solid-state interactions.[5]Non-coordinating anions: 1-2To observe how the [Ag(pep)2]+ motif packs in the solid-state in the absence of strong anion-directing influences, compounds containing traditionally non-coordinative anions were first studied. Hexafluorophosphate and tetrafluoroborate were chosen to identify the primary interactions of [Ag(pep)2]+ that influence the solid-state self-assembly process. Combining two equivalents of pep with one equivalent of silver hexafluorophosphate in acetonitrile yields [Ag(pep)2][PF6]·MeCN (1a). The asymmetric unit contains two non-equivalent linear [Ag(pep)2]+ complexes arrayed orthogonally to each other. First coordination sphere bonds are made to the pyridyl groups of pep within the range of 2.132(7)-2.165(7) ?. Each silver also interacts weakly with one molecule of acetonitrile with an average Ag-N distance of ca. 2.81 ?, and also a hexafluorophosphate counterion (Figure 1, left). The Ag-N-C angle that acetonitrile makes in coordinating to silver varies between the two complexes by 5°. Similarly, the closest Ag-F contacts are unique for each complex. Cumulatively these variations break the symmetry of the two complexes, rendering them crystallographically inequivalent. The complexes pack into a herringbone motif dominated by Ag···? and ?···? interactions between pep ligands, which propagate infinitely along the crystallographic a axis (Figure 1, right). The average distance between the stacks of complexes is 3.27 ? spread across the whole [Ag(pep)2]+ unit, ranging from 3.2784(7) ? to 3,2645(7) ?, dominating the packing interaction. Interestingly, while the Ag···? and ?···? interactions that run down the crystallographic a axis in 1a cumulatively have a prominent influence on the packing arrangement, no noteworthy interactions beyond van der Waals forces were discerned along the crystallographic b or c axes. This lack of stabilization is likely the cause of the spontaneous single-crystal-to-single-crystal (SCSC) transformation observed when crystals of 1a were removed from the acetonitrile medium, resulting in solvent loss and a rearrangement to give [Ag(pep)2][PF6] (1b). This transformation occurs with a slip of the [Ag(pep)2]+ units to bring the central silver atoms into closer alignment, with an Ag···Ag distance of 3.6108(6) ? (Figure 2, left). Void space created by the loss of solvent is filled by the twisting of the pep ligands out of linearity, which breaks the ?···? interactions of the outermost rings that were present in 1a (Figure 2, right). From the angle made by the terminal ring centroids via the silver centre, the [Ag(pep)2]+ cation in 1b is seen to deviate from linearity by more than 25°, facilitated by flexibility of the alkyne functionality within the ligands, and distortion of the N(1)-Ag(1)-N(2) angle to 165.77(10)° (former N-Ag-N angles were 178.4(3)° and 177.4(3)° in 1a). The distortion of one of the pep ligands from Figure 1. Left: Asymmetric unit of 1a, with short contacts shown (Ag1···N5 = 2.800(10) ?, Ag2···N6 = 2.821(10) ?, Ag1···F4 = 3.454(10) ?, Ag1···F5 = 3.435(10) ?, Ag2···F7 = 3.324(10) ?, Ag2···F8 = 3.343(9) ?). Right: Herringbone packing arrangement of 1a, viewed here down the crystallographic b axis, with the Ag···? and ?···? interactions shown in gold. Ellipsoids are depicted at 50% probability.Figure 2. Left: Comparison of the [Ag(pep)2] alignment in structures 1a and 1b. The SCSC slip reduces the Ag···Ag distance from ca 5.0 ? in 1a to 3.6106(8) ? in 1b. Right: Changes to the crystal packing upon formation of 1b showing distortion of pep ligands to fill the void spaces.linearity is greater than 10° as measured from each ring centroid to a point between the alkyne carbons. Key bond lengths and angles include first coordination sphere silver-pep bonding distances of Ag(1)-N(1): 2.132(2) ? and Ag(1)-N(2): 2.138(2) ?.Substitution of the hexafluorophosphate for the tetrafluoroborate salt yields [Ag(pep)2][BF4] (2), which is isostructural with 1b, possessing analogous bond lengths and angles within the [Ag(pep)2]+ complex. While an acetonitrile-containing species analogous to 1a could not be isolated, the same unusual distortions of [Ag(pep)2]+ from linearity observed in 1b were also observed in 2, suggesting that this species likely forms via a similar SCSC desolvation mechanism. Indeed, freshly-prepared crystalline material viewed under a microscope was observed undergoing an SCSC transformation in which larger crystals converted to a multicrystalline material that could be broken up to yield isolated single crystals of 2. The former material proved too unstable to isolate, and of insufficient quality or purity to obtain good X-ray diffraction data.The facile SCSC transformation observed in 1a, and the inferred formation of 2 via a similar mechanism, is likely the result of a lack of dominant ordering interactions within the solid-state packing arrangement of the precursor motif (1a). This, coupled with the ability of the stacked [Ag(pep)2]+ complexes to slip while retaining ?···?, Ag···? and Ag···Ag interactions, and the inherent flexibility of the pep ligand about the alkyne functionality, presents ideal conditions to promote the transformation.NOx anions: 3-5Two NOx anions, nitrite and nitrate, were used to explore how promoting relatively unrestricted anion-derived bridging modes influences the solid-state packing in the Ag-pep complexes. The asymmetric unit of nitrite 3, [Ag(pep)2][Ag(NO2)2], contains a [Ag(pep)2]+ complex and two unique silver atoms, each with half occupancy, ligated by a full occupancy nitrite anion. The nitrite anions chelate via both oxygen atoms to their respective silver atoms, one of which is located on a special symmetry position. Both nitrite-ligated silvers are linked to the central [Ag(pep)2]+ unit by weak interactions derived from the nitrogen atom of the anions. Counting second coordination sphere interactions, Ag(1) of the [Ag(pep)2]+ complex is six coordinate, ligated by N- and O-donors of four unique nitrite anions (Figure 3, left). The remaining silver atoms coordinate only to O-donors of nitrite anions, four for Ag(2) which results in a distorted octahedral arrangement, and three for Ag(3) yielding a distorted square-based pyramid. Both unique nitrite anions in 3 ligate four silver centres in a μ4-η1:η1:η1:η2 manner, or 4.221 according to Harris notation.[20] This creates a 2D network of weak silver-nitrite interactions. Orthogonal to these interactions are the pep ligands, which form continuous rows aligned with the crystallographic b axis and ligate every alternating silver atom (Figure 3, right). This allows the individual layers to interdigitate, aligning the hydrophobic aromatic regions. No strong ?···? or C-H···? interactions are evident for the pep ligands, with the nearest inter- or intra-centroid distances further than 4.6 ?, and hence cumulative van der Waals attraction in the hydrophobic region drive the crystal packing. First coordination sphere bond lengths include equidistant Ag(1)-pep interactions of 2.214(4) and 2.218(4) ?, and silver-nitrite interactions of Ag(2)-O(1),O(2) = 2.413(5) ?, 2.417(4) ?, and Ag(3)-O(3),O(4) = 2.315(6) ?, 2.257(6) ?. Key second coordination sphere bond lengths to silver include Ag(1)-N(3),N(4) = 2.740(5), 2.833(6), Ag(1)-O(3’),O(2’’) = 2.904(4), 2.867(4). This structure is also Figure 3. Left: The 2D array formed from weak interactions in 3, comprised of three unique silver atoms, and two unique nitrite counter anions. The pep ligands ligate only to Ag(1), whereas Ag(2) and Ag(3) are ligated only by O-donors of nitrite anions, in a 6- and 5-coordinate manner, respectively. Right: Pillared pep ligands as viewed down the crystallographic b axis. Interdigitation of the 2D nets dominate the crystal packing.interesting in that the two pep ligands within the [Ag(pep)2]+ complex do not have planar alignment, exhibiting instead a dihedral angle of 57°.The investigation of the pep / silver nitrate complexes was complicated by the discovery that varying the ratios of the reagents yielded two distinct solid-state structures. When an excess of pep was used, 1D chains of [Ag(pep)2][NO3]·2H2O (4) were isolated as colourless crystals. In contrast, an excess of silver nitrate resulted primarily in a second species, [Ag(pep)2][Ag(NO3)2] (5), which formed a 2D sheet motif. Both 4 and 5 could be preferentially synthesized by careful control of the reaction stoichiometry.The asymmetric unit of the hydrated structure 4 contains the [Ag(pep)2]+ unit with a nitrate anion and two waters of crystallization, which form a hydrogen-bonded network. The Ag(I) centre formally has linear covalent bonds with pep, but four weak interactions derived from three nitrate anions give an informal coordination number of six. These noncovalent interactions have distances of Ag1-O1 = 2.638(4) ?, Ag1-O1’ = 2.643(4) ?, Ag1-O3 = 3.112(6) ? and Ag1-O3’’ = 3.061(5) ?, respectively (Figure 4, left). Overall, chains of alternating silver nitrate interact with hydrogen-bonding water molecules to give a continuous 2D network based on polar interactions. The water molecules compete with silver to hydrogen bond with nitrate anions, and this may inhibit the formation of the chelative binding modes seen in 3. The pep ligands are aligned in a zig-zag pattern orthogonal to the 2D silver anion chain. Much like in nitrite structure 3, the alignment of pep ligands creates an interdigitated hydrophobic layer that serves to partition the polar silver anion and hydrogen-bonded water regions (Figure 4, right). Also consistent with 3 was a lack of strong inter-ligand ?···? or C-H···? interactions, with matching centroids separated by more than 4.7 ?.Figure 4. Left: Network formed from non-covalent interactions (dashed lines) observed within the [Ag(pep)2][NO3]·2H2O structure of 4, linking together covalent 1D chain motifs. The pep ligand has been omitted for clarity. Symmetry operations: (‘) = {-x, 1-y, z-?}, (“) = {-x, 1-y, ?+z}. Right: Arrayed pillars of pep ligands as viewed down the approximate crystallographic c axis. Interdigitation of the 2D layered structure of 4 dominates the crystal packing between layers. Hydrogen atoms and water molecules have been excluded for clarity.The second nitrate-containing structure, [Ag(pep)2][Ag(NO3)2] (5), was selectively obtained by addition of an excess of the silver salt. This promoted incorporation of a greater proportion of the silver salt into the material, resulting in a 2D layered structure free of water molecules. The asymmetric unit of 5 contains two unique silver atoms, one coordinated by two pep ligands, the other ligated by two charge-balancing nitrates. The [Ag(pep)2]+ unit is distorted, particularly the angle made by one of the coordinating pyridyl groups, which deviates from the ideal coordination angle by more than 17° measured from the pyridyl centroid to the silver via the coordinating nitrogen atom. This distortion is likely due to steric congestion, owing to the influence of a Ag···Ag interaction with a distance of 2.7904(6) ?, which is well within the sum of the van der Waals radii of two silver atoms (3.44 ?).[21] In addition to the Ag-pep interactions, the second silver atom is ligated by three nitrates, with first coordination sphere bond lengths of Ag(2)-O(1) = 2.453(5) ?, Ag(2)-O(1’) = 2.468(5) ?, Ag(2)-O(2) = 2.500(4) ? and Ag(2)-O(4) = 2.310(5) ?. Both silver centres are seven coordinate once second coordination sphere and argentophilic interactions are counted, with Ag(1) ligated by both pep ligands and two nitrates in a bidentate fashion, while Ag(2) chelates to three bidentate nitrates (Figure 5, left). Silver-nitrate interactions in 5 form a 2D layered network analogous to 3. Within the layered motif there are two unique nitrate anions bridging two and three silver centres respectively. The first nitrate bridges two silver centres in a μ2-η2:η2 manner, or 2.211 in Harris notation, while the second bridges three silver centres in a μ3-η2:η2:η2 manner, or 3.222 in Harris notation.[20] Interdigitation of rows of pep ligands fuse the layered motifs together, yielding the final structure (Figure 5, right).Figure 5. Left: The 2D network formed from weak interactions (dashed lines) in 5, comprised of Ag+ and NO3-. The pep ligand has been omitted for clarity. Right: Arrayed pillars of pep ligands, as viewed down the approximate crystallographic b axis. Interdigitation of the 2D layered structure of 5 dominates the crystal packing between layers. Hydrogen atoms have been excluded for clarity.Carboxylate and sulfonate anions: 6-9Changing the NOx anions for acetate leads to a narrowing of the available anion-chelation region through the introduction of a non-bonding methyl group. The resulting 1D chain of [Ag(pep)2(MeCO2)]·3H2O (6) (Figure 6), is comparable to the structure of hydrated nitrate 4, albeit with covalent bonding within the chain. Unlike in 4, the methyl group of the acetate in 6 prevents hydrogen-bonding interactions between the silver anions and the adjacent lattice water molecules, causing a decrease in their solid-state ordering. Consequently, the positions of the solvent water molecules in 6 were highly disordered, and thus were omitted from the crystallographic Figure 6. Covalent 1D chain structure of acetate 6. The pep ligand has been omitted for clarity. Symmetry operations: (‘) = {-x, 1-y, z-?}.Figure 7. Left: The pseudo-paddlewheel configuration within the structure of [Ag(pep)2][CF3CO2] (7a). Dashed gold lines indicate ?···? and Ag···Ag interactions, and anion-based weak interactions are shown as red dashed lines. Hydrogen atoms have been omitted for clarity. Right: Herringbone packing arrangement of 7a, viewed here down the crystallographic c axis.model. The presence of three water molecules was determined by TGA analysis (Figure S2). The packing motif of acetate 6 was found to be isostructural with the pillared motif exhibited by 4 (Figure 4). Key bond lengths include Ag(1)-O(1) = 2.484(6) ?, Ag(1)-O(1’) = 2.543(5) ? and a longer range interaction of Ag(1)···O(2): 2.708(10) ?.Replacement of acetate by trifluoroacetate sterically rotates the carboxylate ‘bite’ angle to disfavour the 1D chain formation observed in 6. Instead, the two [Ag(pep)2]+ units of 7a align into a dimeric species linked by a Ag···Ag interaction (d = 3.1171(3) ?) and by ?···? interactions located between the pyridyl rings (intercentroid d = 3.63 ?) (Figure 7, left). The trifluoroacetates interact only weakly with the [Ag(pep)2]+ units, adopting μ2-η2:η bridging modes with distances of Ag(1)-O(1) = 2.7700(16) ?, Ag(1)-O(2) = 2.6039(16) ? and Ag(1)-O(2’) = 2.6039(15) ?. Thus the four pep ligands and two trifluoroacetate groups combine to give 7a a pseudo-paddlewheel arrangement about the two silver centres.The packing of 7a forms a herringbone motif, wherein the pseudo-paddlewheels align in an offset manner (Figure 7, right). Interestingly, the only weak interactions discerned in the solid-state were found within the paddlewheel motif, specifically the aforementioned Ag···Ag and ?···? interactions. No compelling ?···? or C-H···? interactions could be inferred linking the paddlewheel motifs. All other aromatic rings contacts are both misaligned for ?···? stacking and have intercentroid distances greater than 3.9 ?. These observations suggest that the dimeric [Ag(pep)2]2[CF3CO2]2 may initially self-assemble in solution, followed by relatively inefficient packing upon crystallization that prevents optimal solid-state intermolecular interactions from forming.As the herringbone structures of 1a and the precursor to 2 were found to be metastable and susceptible to SCSC transformations, 7a was investigated for similar activity. This was achieved initially by using differential-scanning calorimetry (DSC) to scan for potential phase changes between ambient temperature and 250 °C. The DSC scan (Figure S3) revealed two endothermic events, a phase transition occurring over the range of 165 – 169 °C, followed by clear melting event in the range of 199 – 201 °C. Heating a sample of crystalline 7a above this phase-transition temperature results in formation of a new material, 7b, with a colour change from colourless to orange (Figure 8).Figure 8. Top: A comparison between the pseudo-paddlewheel units in 7a (blue) and 7b (orange). Bottom: Crystalline sample of 7a (left) before and after heating above 170 °C for 1 hour, yielding the orange product 7b (right). Figure 9. Changes in the packing through the phase transition of 7a to 7b resulting in more widespread ?···? interactions that stabilize the latter. Hydrogen atoms have been omitted for clarity.Analysis of the crystalline product 7b by single crystal X-ray diffraction methods identified a new, albeit closely-related, structure to the pseudo-paddlewheel structure of 7a. An overlay of the pseudo-paddlewheel motifs (Figure 8, top) shows increased interaction between the silver and the trifluoroacetate anion in 7b (Ag···O = 2.6039(16) ? for 7a; 2.550(3)) ? for 7b), concomitant with an increase in the length of the argentophilic interaction (Ag···Ag = 3.1171(3) ? for 7a; 3.1830(6) ? for 7b). Changes to the solid-state packing between the two structures are far more pronounced (Figure 9). While the herringbone motif was retained in 7b, shifting of the pep ligands and the relative positions of the pseudo-paddlewheels allows each [Ag(pep)2]+ unit to participate in a total of seven ?···? interactions within the inter-centroid limit for ?···? stacking of 3.8 ?,[22] a more than threefold increase relative to 7a.To establish the microscopic origin of the colour change on conversion from 7a to 7b, we carried out first-principles computational modelling on the two systems using periodic DFT.Taking the X-ray structures of 7a and 7b as a starting point, we first relaxed the atomic positions and the cell shapes of the two, keeping the volume fixed at the experimentally-determined values, and then carried out more accurate hybrid electronic-structure calculations to characterize the crystal orbitals and associated energies, and to model the optical properties (Figure 10). Optimization did not change the unit-cell parameters from the experimental values, and key bond lengths around the Ag atoms were found to be in good agreement with those of the initial structures (see Supp. Info. for data).Figure 10 (a) compares the energy-level spectra of the 7a and 7b, referenced to the average of the C 1s core eigenvalues. The structural changes occurring through the SCSC transformation lead to a general upward shift in the energies of the occupied orbitals, together with a lowering in the energy of the unoccupied states. This together leads to a decrease in the energy gap between the highest-occupied and lowest-unoccupied crystal orbitals (HOCO/LUCO) from 3.838 eV in the colourless 7a to 3.768 eV in the orange 7b.The simulated absorption spectra (Figure 10 (b)) predict a red shift in the absorption profile of 7b compared to 7a, which is consistent with the observed colour change and confirms that the shifts in the energy levels visible in Figure 10 (a) is reflected in the absorption profiles. The respective HOCO-LUCO gaps of the two systems lie in a long-wavelength tail of the absorption profile, where the absorption coefficient is comparatively small; this suggests that perturbations to the fairly large density of states around the band edges, as well as to the frontier orbitals, may be responsible for the colour shift. We note that the basic independent-particle formulation of time-dependent density-functional theory (TD-DFT) used in these calculations should not be expected quantitatively to reproduce the positions of absorption bands,[23] and it may be that the strong UV absorption below ~300 nm would be shifted to longer wavelengths if a more accurate solid-state TD-DFT method were used. Nonetheless, the present calculations are sufficient for a qualitative comparison.Figure 10. Computational modelling of the electronic structure and optical properties of the colourless 7a and the orange 7b. (a) Energy-level spectrum of the two materials, with the energy gaps between the highest-occupied and lowest-unoccupied crystal orbitals (HOCO/LUCO) marked in blue. (b) Simulated wavelength-dependent absorption coefficients. The positions of the HOCO-LUCO gaps are marked on the two spectra by blue stars. (c, d) Density plots of the HOCO (top/left) and LUCO (bottom/right) of 7a (c) and 7b (d). The images in (c) and (d) were prepared using the VESTA software.[24]From density plots of the frontier orbitals of the two systems (Figure 10 (c, d)), the HOCOs of both are composed mainly of Ag dz2 orbitals, with small contributions from coordinated heteroatoms, whereas the LUCOs are formed of the ligand ? systems. The energy-level spectrum suggests that the reduction in the energy gap, and corresponding colour shift, in 7b relative to 7a is due to the combination of a stabilization of the unoccupied orbitals and a destabilization of the occupied states, both of which can be interpreted in terms of the main structural changes across the transformation observed from the crystallography, viz. an increase in the Ag···Ag interaction distance, which, if the metal dz2 orbitals on adjacent Ag atoms interact out of phase, would destabilize the HOCO, and an increase in ?···? interactions between ligands, which could stabilize the LUCO.Changing the chelating group from carboxylate to sulfonate in 8 while retaining the trifluoromethane group yields a 1D ladder motif, indicative of weak anion-[Ag(pep)2]+ interactions. Three [Ag(pep)2]+ units are coordinated by each sulfonate anion, one per oxygen donor of the sulfonate (Figure 11, left); each silver atom possesses a linear first coordination sphere, which becomes a distorted trigonal bipyramid once second coordination sphere anion interactions are included (? value = 0.63).[25] This gives 8 a molecular formula of [Ag(pep)2][CF3SO3]. Key bond lengths include Ag(1)-O(1) = 2.913(5) ?, Ag(1’)-O(3) = 2.975(7) ? and Ag(1’’)-O(2) = 2.742(7) ?. The hydrophobic trifluoromethyl group sterically shields the sulfonate group, removing the possibility of hydrogen bonding interactions to any potential lattice solvents within 8 (Figure 11, right). This, coupled with the larger size of the sulfonate anions, allows a similar packing motif to that in nitrate species 5 to occur without the need for additional silver anion equivalents or solvent molecules to fill void space.Figure 11. Left: Weak anion-derived interactions yielding a 1D ladder motif in sulfonate 8. The pep ligand has been omitted for clarity. Symmetry operations: (‘) = {-x, ?+y, -z}, (“) = {-x, y-?, -z}. Right: Water molecules formally present in the related motifs of 3 and 6 are sterically displaced by the larger triflate anion. Pillars of pep ligands are viewed here down the approximate crystallographic b axis. Interdigitation dominates the crystal packing between layers. Hydrogen atoms have been excluded for clarity.Further increasing the steric bulk of the sulfonate anion by substituting the triflate anion for tosylate in 9 yields the same 1D ladder motif observed in 8 (Figure 12, (a)). The larger p-tosyl group forces the 1D chains apart, creating a channel that is filled by a non-coordinated pep molecule (Figure 12, (b)). This gives an overall molecular composition of 2{[Ag(pep)2][Tos]}·pep for 9. The silver centre is formally linear, but once second coordination sphere bonds are considered has distorted trigonal bipyramidal coordination geometry (? value = 0.78).[25] Weak silver-Tos interactions within 9 include Ag(1)-O(1) = 2.636(4) ?, O(2)-Ag(1’) = 2.831(3) ? and O(3)-Ag(1”) = 2.864(3) ?.While no ?···? interactions were observed for the silver-coordinated pep ligands, the non-coordinating pep ligand sits at the centre of twelve weak interactions: four C-H···? interactions, and eight derived from C-H···Tos hydrogen bonds (Figure 12, (c)). The perpendicular T-shaped ? interactions occur with a carbon-centroid distance of 3.44 ?, while the C-H···Tos hydrogen bonds have C···O distances of either 3.350(6) or 3.455(6) ?. It is likely that the large number of complementary interactions attributed to the non-coordinated pep (Fig. 12c) in the structure of 9 ensure that the 3:1 ratio of ligand to metal salt is observed as the kinetic product of the reaction, despite a 2:1 ratio being employed during synthesis. Figure 12. (a) 1D ladder motif observed in 9, which is isostructural to 8. The pep ligand has been omitted for clarity. Symmetry operations: (‘) = {1-x, 1-y, 1-z}, (“) = {x, y-1, z}. (b) Inclusion of non-coordinated pep ligands (shown with space-filling atoms) into the voids formed due to the inclusion of the tosylate anion, viewed here down the crystallographic b axis. Hydrogen atoms have been excluded for clarity. (c) Well aligned C-H···Tos weak hydrogen bonds and C-H···? interactions stabilize the non-coordinated pep molecule within the solid-state lattice of 9.Thiocyanate anion: 10The final structure in the present study proved exceptional in that the [Ag(pep)2]+ unit did not form when pep was combined with silver thiocyanate. Instead a 2D sheet network propagated by silver-thiocyanate interactions was observed, with a composition of [Ag(pep)(SCN)]. The 2D sheet in 10 is comprised entirely of Ag-N and Ag-S coordination bonds (Figure 13, left). The key interactions which stabilize the network are Ag(1)-N(2) = 2.164(3) ?, Ag(1)-S(1’) = 2.6139(9) ? and Ag(1)-S(1”) = 2.6403(9) ?. The silver-pep interaction is longer than in structures 1-9, with a distance of Ag(1)-N(1) = 2.305(2) ?. The pep ligands form alternating pillared arrays (Figure 13, right), promoting interdigitation between the 2D sheets. This structure highlights the influence that a strong N-donor anion may have over a neutral N-donor ligand. The additional availability of S-donor interactions in 10 results in the only 2D coordination polymer observed in this study. The strength of these N- and S-donor anion interactions impedes formation of the weak interactions targeted by this study, and thus other N- and S-donor anions were not evaluated. Analogous sheet motifs have been observed with other pyridyl ligands,[26] however increasing steric bulk of the ligand typically favours 1D chains and 0D clusters of silver and thiocyanate.[27]This species was also found to deviate from the synthetically employed 2:1 ratio used in relation to ligand and metal salt. It is likely that the bridging modes provided by thiocyanate between silver centres may lead to crowding at the metal centre, disfavouring inclusion of more than one equivalent of pep during crystal formation. Similarly the ability of thiocyanate to impart strong interactions likely provides a kinetic advantage for structure 10 that is absent in structures containing more weakly coordinating anions. Figure 13. Left: The 2D sheet motif of 10 comprised of covalent Ag-N and Ag-S bonds from thiocyanate. The pep ligand has been omitted for clarity. Right: Arrayed pillars of pep ligands that propagate along the crystallographic a axis. Interdigitation of the 2D sheet motifs dominates the crystal packing between layers. Hydrogen atoms have been excluded for clarity.By systematically exploring the chemistry of a single well-defined synthon, we have been able to identify trends that will aid in targeting specific structural motifs, and, by extension, improve control over material properties. In every instance, the formation of 1D chains, ladders or 2D sheets resulted in a packing motif dominated by interdigitation, regardless of whether covalent or weak interactions linked the silver centres to the anions. In structures where interdigitation did not occur, examples of SCSC behaviour were prevalent, typically initiating from arrayed 0D complexes. The degree of covalency in the structure also appears to influence the Ag-N bond length in the [Ag(pep)2]+ unit. Covalent character was observed in structures 5, 6 and 10, resulting in longer than average silver-pep bond lengths of 2.18 ?, 2.28 ? and 2.31 ?, respectively. Two of these average bond lengths are longer than the entire range of silver-pep bond lengths for structures without covalent character (2.132(2) ? - 2.193(3) ?).This work serves to complement other examples of SCSC transformations exhibited by silver complexes that have been triggered by photo-dimerization of alkene-functionalized ligands.[4b-e] While our investigations found no evidence of solid-state photochemistry involving the alkyne group in pep, both thermal and desolvation triggers were found to be sufficient to yield SCSC transformations in two paring this work with known examples of silver pyridine complexes identified a decline in the variability of observed motifs upon increasing the ligand length. Several silver pyridine structures do adopt a linear [Ag(py)2]+ complex, particularly when paired with non-coordinating anions,[28] or a rigid polymeric component of the structure.[29] However, the sterically less restrictive size of pyridine, coupled with a lower affinity for interdigitation and ?-? staking interactions, gives rise to a number of other silver coordination geometries, including tetrahedral[30] and heteroleptic complexes with T-shaped Ag(py)3 metal nodes.[29b] The preference for thiocyanate to disrupt the [Ag(py)2]+ motif in favor of polymeric [Ag(py)(SCN)] 2D sheets can also be observed using pyridine as the ligand.[31] The higher affinity for metallophilic interactions in gold complexes contributed heavily to 1D chain formation in the solid-state structures featuring analogous linear [Au(py)2]+ complexes.[32] It should however be noted that these studies almost exclusively focused on halide counteranions, which were not explored in this work.In summary, the [Ag(pep)2]+ unit is an excellent precursor for generating materials for systematically probing weak interactions in the solid-state. By focusing on non-coordinating, NOx, carboxylate and sulfonate counter-anions, this study has identified eleven solid-state structures (1-9) to further these aims. As silver(I) typically forms very few covalent interactions, the pep ligands were generally found to dominate the covalent interactions within these structures, ensuring typically weak bonding to the anions, even those such as nitrate, trifluoroacetate and the sulfonates. However, strong interactions between thiocyanate and silver prevented formation of the [Ag(pep)2]+ unit in 10, which consequently reduced the prevalence of weak interactions within this network. The family of structures 1-9 allowed some structure-property relationships within this family to be established, in particular pertaining to targeting SCSC rearrangements in 0D solid state structures. Ensuring that weak interactions are dominant within the solid-state packing while discouraging interdigitation appears to be a useful strategy for increasing the likelihood of SCSC transformations. We believe this behaviour will be applicable to pyridyl ligands in a more general sense, and we aim to investigate this in future studies.ConclusionsThis study has identified twelve solid-state structures within a family of silver complexes ligated with 4-(phenylethynyl)pyridine. Of these twelve structures, the crystal packing in the eleven contained within the family 1-9 is predominantly dominated by weak, non-covalent interactions within the solid-state crystalline packing. These structures were derived from a range of counter anions comprising PF6-, BF4-, NO2-, NO3-, MeCO2-, CF3CO2-, MeSO3- and Tos-. The majority of these structures exhibit a 2:1 ligand to metal ratio, the exceptions being 3 and 5 which possess a 1:1 [Ag(pep)2][AgX2] (X = NO2, NO3) ratio, and 9 which contains non-coordinated pep in its lattice giving a 3:1 ratio. The thiocyanate anion, SCN-, also resulted in a 1:1 [Ag(pep)(SCN)] product that resulted in no discernable weak interactions in the solid-state structure 10, most likely due to ready availability of strong N- and S-donor anion interactions relative to the neutral pyridyl coordination of pep. Structure-property relationships pertaining to the weak non-covalent interactions were investigated, particularly the possibility of SCSC transformations. Two SCSC transformations were identified and characterized explicitly, and a third inferred by observation and analogy. Of these, the 1a to 1b transformation occurs with desolvation and bending of the [Ag(pep)2]+ unit by more than 24°, while the 7a to 7b transformation is concomitant with an increase in ?···? stacking and a decrease in Ag···Ag interactions, and this occurs with a change in the colour of the crystals. This second SCSC transformation was explored using DFT calculations, which attribute the change in colour to changes in the frontier-orbital energies due to the differences in packing.Experimental SectionMaterials and Equipment: All chemicals used in this study were purchased from commercial sources and used without further purification. Infrared (IR) spectra were recorded on a PerkinElmer Spectrum 100 spectrometer equipped with an ATR-sampling accessory. Abbreviations for IR bands are s – strong, m – medium, w - weak. Elemental analyses (C, H, N) were performed at the Science Centre of London Metropolitan University. Thermogravimetric analysis (TGA) was performed using a Setsys Evolution TGA 16/18 from Setaram with Calisto software to collect and process the data. Samples were placed in 170 ?L alumina crucibles and prior to experiments the analytical chamber was purged from ambient air using argon flow at 200 mL/min for 40 min. Sample pans were analyzed under argon flow at 20 mL/min. Powder X-ray diffraction data was also collected for compounds 1-10 (excepting 1b and 7b) on a Bruker AXS D8 Advance diffractometer with copper Kα radiation of wavelength 1.5406 ? at 298 K. Samples were placed on a flat plate, and measured with a 2θ range of 5-40°. Simulated X-ray powder patterns were generated from single crystal data that were imported into PowderCell. These data are presented as Supporting Information. Synthesis of 4-(phenylethynyl)pyridine: 4-(phenylethynyl)pyridine (pep) was prepared by a Sonogashira coupling of 4-bromopyridine hydrochloride (1.00 g; 5.1 mmol) and phenylacetylene (0.55 ml; 5.0 mmol) in the presence of bis(triphenyphosphine)palladium dichloride (72.3 mg; 2 mol%) and CuI (9.8 mg; 1 mol%) in degassed triethylamine (2.1 ml) over 4 days under an atmosphere of nitrogen.[33] After the reaction was complete, as gauged by thin-layer chromatography, the product was extracted with a basic workup and purified by silica gel chromatography. Yield of isolated product: 760 mg (85 %). 1H NMR (300 MHz, DMSO-d6): δ = 8.64 [d, 3J(H-H) = 5.7 Hz, 2 H, Py], 7.63 (m, 2 H, Py), 7.54 (m, 2 H, Ph), 7.48 (m, 3 H, Ph) ppm. 13C NMR (75 MHz, DMSO-d6): δ = 150.0 (Py), 131.8 (Ph), 130.2 (Py), 129.7 (Ph), 128.9 (Ph), 125.4 (Ph), 121.2 (Py), 93.5 (C≡C), 86.7 (C≡C) ppm. IR (ATR): ? = 3470 (w), 2222 (m), 1606 (m), 1502 (w), 1296 (s), 1217 (s), 1160 (w), 1068 (m), 1018 (m), 833 (s), 801 (m), 765(s), 690 (s) cm-1. HRMS (ESI+, MeOH): m/z (%) = 180.0828 (calcd. 180.0813) [M + H]+.General procedure for synthesizing silver coordination complexes 1-10: Note: Ag(I) salts decompose in ambient light and therefore all crystallizations were covered in aluminium foil for the duration of the reaction. After that, all crystalline samples were found to be stable when exposed to light. A solution of 4-(phenylethynyl)pyridine (5 mg; 0.027 mmol) dissolved in methanol or acetonitrile (0.6 ml) was added to the appropriate silver(I) salt (0.014 mmol) with sonication. Once dissolved, the mixture was sealed and heated to 40 °C for 30 mins in the absence of light. After cooling to room temperature, the vial was opened slightly to allow slow evaporation of the solvent while protecting the solution from light. The resulting crystals were washed with a 1:4 MeOH/H2O mixture prior to characterization.[Ag(pep)2][PF6]·MeCN 1a: Colourless needles suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 7.2 mg (79 %). IR (ATR): ? = 2223 (m), 1608 (m), 1504 (w), 1428 (m), 1221 (m), 1066 (w), 1027 (w), 818 (s), 761 (s), 693 (s) cm-1. Despite repeated attempts, single crystals of 1a sent for elemental analyses matched ratios expected for 1b, suggesting SCSC conversion and desolvation occurs en route. [Ag(pep)2][PF6] 1b: Prismatic crystals suitable for X-ray diffraction were obtained by a SCSC transformation after air-drying 1a. Yield of isolated product: Quantitative based on 1a. IR (ATR): ? = 2223 (m), 1608 (m), 1504 (w), 1428 (m), 1221 (m), 1066 (w), 1027 (w), 818 (s), 761 (s), 693 (s) cm-1. C28H21AgF6N3P (652.3): calcd. C 51.09, H 2.97, N 4.58; found C 50.98, H 2.89, N, 4.66.[Ag(pep)2][BF4] 2: Colourless plate crystals suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 3.5 mg (45 %). IR (ATR): ? = 3527 (w), 2220 (m), 1607 (m), 1501 (m), 1426 (m), 1282 (w), 1218 (m), 1017 (s), 828 (s), 755 (s), 687 (s) cm-1. C26H18AgBF4N2 (553.1): calcd. C 56.46, H 3.28, N 5.06; found C 56.31, H 3.45, N 5.04.[Ag(pep)2][Ag(NO2)2] 3: Colourless prismatic crystals suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 7.3 mg (78 %). IR (ATR): ? = 3079 (w), 2222 (m), 2165 (w), 1604 (m), 1542 (w), 1499 (m), 1442 (w), 1416 (m), 1216 (s), 1069 (w), 1015 (w), 925 (w), 829 (s), 766 (s), 692 (s) cm-1. Elemental analysis determined the bulk sample contained a small excess of silver nitrite. Anal. Calcd (%) for C26H18Ag2N4O4·0.2AgNO2 (666.2): calcd. C 44.81, H 2.60, N 8.44; found C 44.83, H 2.64, N 8.50. Note: Varying the metal-to-ligand ratio was attempted however this did not improve purity of 3.[Ag(pep)2][NO3]·2H2O 4: Colourless needles suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 6.3 mg (67 %). IR (ATR): ? = 3248 (m), 2222 (m), 1605 (m), 1502 (w), 1427 (w), 1339 (s), 1217 (m), 1160 (w), 1069 (m), 1018 (w), 883 (s), 766 (s), 691 (s) cm-1. C26H18Ag2N3O3·1.25H2O (658.7): calcd. C 56.69, H 3.75, N 7.63; found C 56.81, H 3.81, N 7.63.[Ag(pep)2][Ag(NO3)2] 5: Compound 5 was isolated in high purity using a higher metal-to-ligand ratio of 1.1:1. Ag(NO3) = 5.1 mg, 0.030 mmol; pep: 5.0 mg; 0.027 mmol. Colourless block crystals suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 6.2 mg (64 %). IR (ATR): ? = 3363 (m), 2220 (m), 1501 (w), 1419 (w), 1376 (w), 1290 (s), 1215 (m), 1069 (w), 1018 (m), 924 (w), 830 (s), 810 (m), 763 (s), 689 (s) cm-1. C26H18Ag2N4O6 (698.2): calcd. C 44.73, H 2.60, N 8.02; found C 45.21, H 2.63, N 7.87.[Ag(pep)2(MeCO2)]·3H2O 6: Colourless needles suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 4.9 mg (60 %). IR (ATR): ? = 3363 (w), 3071 (w), 2223 (m), 1552 (m), 1497 (m), 1395 (m), 1214 (s), 1071 (w), 1007 (w), 922 (m), 834 (s), 760 (s), 690 (s) cm-1. Despite repeated attempts, satisfactory elemental analysis data could not be obtained for this material.[Ag(pep)2][CF3CO2] 7a: Colourless prismatic crystals (7a) and orange prismatic crystals (7b) were obtained in the same vial after 48 h. Sufficient material could be isolated by crystal picking to characterize 7a. Combined yield: 5.8 mg (71 %). IR (ATR): ? = 3443 (m), 3065 (w), 2219 (m), 1666 (s), 1606 (s), 1544 (w), 1502 (m), 1442 (m), 1428 (m), 1414 (m), 1198 (s), 1180 (s), 1111 (s), 1021 (m), 924 (w), 829 (s), 795 (s), 752 (s), 717 (s), 688 (s) cm-1. Elemental analysis determined the bulk sample to contain a small excess of silver triflate. C28H18AgF3N2O2·0.1AgCF3CO2 (579.3): calcd. C 56.32, H 3.02, N 4.66; found C 55.94, H 2.96, N 4.62. [Ag(pep)2][CF3CO2] 7b: Orange prismatic crystals of 7b were concomitantly obtained during the synthesis of 7a that provided sufficient material to obtain single crystal diffraction data and IR analysis. IR (ATR): ? = 3077 (w), 2220 (m), 1670 (s), 1603 (s), 1541 (w), 1500 (m), 1444 (m), 1416 (m), 1218 (m), 1198 (s), 1181 (s), 1105 (s), 1072 (m), 1011 (m), 924 (w), 829 (s), 794 (s), 755 (s), 718 (s), 691 (s) cm-1. While 7a could be converted to 7b thermally as shown by DSC and confirmed by unit cell comparison, material produced by this method did not give satisfactory elemental analysis results implying partial decomposition. [Ag(pep)2][CF3SO3] 8: Colourless irregular crystals suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 8.6 mg (99 %). IR (ATR): ? = 2222 (m), 1608 (m), 1544 (w), 1503 (w), 1429 (m), 1252 (s), 1219 (s), 1172 (m), 1141 (m), 1069 (w), 1023 (s), 923 (w), 855 (w), 826 (s), 766 (s), 690 (s), 632 (s) cm-1. C27H18AgF3N2O3S (615.4): C 52.70, H 2.95, N 4.55; found C 52.73, H 2.86, N 4.59.2{[Ag(pep)2][Tos]}·pep 9: Colourless plate crystals suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 4.3 mg (42 %). IR (ATR): ? = 3061 (w), 2219 (m), 2165 (w), 1601 (m), 1538 (w), 1498 (w), 1442 (w), 1413 (m), 1188 (s), 1117 (m), 1031 (m), 1009 (m), 922 (w), 821 (s), 761 (s), 677 (s) cm-1. C79H59Ag2N5O6S2 (1454.2): C 63.68, H 4.01, N 4.64; found C 63.64, H 3.96, N 4.78.[Ag(pep)(SCN)] 10: Colourless block crystals suitable for X-ray diffraction were obtained after 48 h. Yield of isolated product: 4.8 mg (99 %). IR (ATR): ? = 2220 (m), 2112 (s), 1601 (m), 1589 (m), 1538 (w), 1497 (w), 1441 (w), 1412 (m), 1213 (w), 1003 (w), 825 (s), 762 (s), 691 (s) cm-1. C14H9AgN2S (345.2): C 48.72, H 2.63, N 8.12; found C 47.19, H 2.90, N 7.86. Note: Varying the metal-to-ligand ratio to 1:1 did not impact the yield, however the product was determined to be of lower purity to the 1:2 ratio by elemental analysis.X-ray Crystallography: Crystallographic data for 1-10 has been provided in Table 1. X-ray diffraction data for 1, 3-6 and 8-9 were collected on an Agilent Technologies SuperNova, EosS2 diffractometer at 150 K using a standard Cu or Mo microfocus source. Diffraction data for 2, 7a, 7b and 10 were collected on a Bruker Apex2 CCD diffractometer at 100 K using synchrotron radiation (Station 11.3.1, Advanced Light Source, Berkeley). For each experiment, a suitable crystal was selected, mounted in oil and kept at either 100(2) K or 150(2) K during data collection. All structures were solved by direct methods using either SHELXS[34] or SIR2004[35] and refined by least-squares minimization using SHELXL.[34] Xseed[36] or Olex2[37] were used as an interface for the SHELXL program. All non-hydrogen atoms were refined by using an anisotropic model. Hydrogen atoms were refined at calculated positions using a riding model. Variata: 1a: Likely owing to the facile nature of 1a towards undergoing SCSC transformation, the crystal was found to degrade with time, impacting data completeness and resolution. While the connectivity is unambiguous, the bond parameters should be treated with caution. 2: Likely owing to this material’s origin as an SCSC product, the crystal batch was weakly diffracting and, even with synchrotron radiation, the resolution limit for observable data was 26° in theta. 5: An oxygen atom (O4) was constrained by the ISOR command as it appeared to exhibit a minor disorder component, however this could not sustain refinement. 6: This structure was refined as a two-component inversion twin, with each component scaled at 0.81(8) 0.19(8). The water molecules lacked solid-state ordering and could not be modelled. Consequently the electron density in the solvent channel was removed using squeeze. A solvent accessible void volume of 210 ?3 and an electron count of 65 was found. 7a: The crystals were weakly diffracting with no observable reflections above 26° in theta, hence a low resolution limit was used. 7b: Likely owing to this material’s origin as a SCSC product, the crystals were found to be weakly diffracting and only low resolution data could be obtained. There was no measurable data above 26° in theta, hence the low limit was set. This structure was additionally refined as a two-component inversion twin, with each component scaled at 0.7524(8) 0.2476(8). 9: Only one quarter of the non-coordinated pep ligand was present within the asymmetric unit, as a result of translational disorder of the alkyne group and overlapping inversion disorder of the rings. To achieve a sensible model the alkyne carbons, lying on the crystallographic mirror plane were constrained to have a total occupancy of 0.5, while either adjacent ring atom position, also lying on the mirror plane, was occupied by a carbon atom constrained to 0.375 and nitrogen atom constrained to 0.125, each sharing their relative coordinates by means of the EXYZ command in SHELXL,[34] to give a total occupancy of one atom for each of these sites. The thermal parameters for the carbon/nitrogen couplets were constrained by the EADP command, as were the alkyne carbons atoms. Finally DFIX and DANG restraints were used to restrain the ring into a half-hexagon DC 1475784-1475795 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre. Computational Modelling: To establish the origin of the difference in colour between the two polymorphs, computational modelling was carried out on 7a and 7b. First-principles calculations were performed within the pseudopotential plane-wave density-functional theory (DFT) formalism, as implemented in the Vienna Ab initio Simulation Package (VASP) code.[38] The X-ray structures of 7a and 7b were taken as starting points, and the atomic positions and cell shapes were optimized with the PBEsol generalized-gradient approximation (GGA) functional[39] until the magnitude of the forces on the ions was less than 10-2 eV ?-1. The cell volumes were fixed to the experimentally-determined values. More accurate single-point calculations were then carried out on each relaxed structure with the HSE 06 screened hybrid functional,[40] from which the orbital energies, density isosurfaces of the highest-occupied and lowest-unoccupied crystal orbitals (HOCOs/LUCOs), and the dielectric functions, and hence frequency-dependent optical-absorption coefficients, were obtained. A plane-wave basis with a kinetic-energy cutoff of 850 eV was used to represent the electronic wavefunctions, with projector-augmented wave (PAW) pseudopotentials[41] being used to treat the core electrons. The pseudopotentials used in this work model the H 1s, the C, N, O and F 2s and 2p, and the Ag 5s, 4d and semicore 4p electrons as valence. The electronic Brillouin zone was modelled at the zone centre (the point). The chosen plane-wave cutoff and k-point sampling were sufficient to converge the absolute values of the total energies to within 1 meV atom-1, and the stress tensors to within 1 kbar (0.1 GPa). During the self-consistent optimization of the electronic wavefunctions, a tolerance of 10-8 eV was applied to the total energy. The PAW projection was performed in real space during the geometry optimization, and in reciprocal space during the subsequent hybrid calculations. The dielectric functions were evaluated within the independent-particle formalism implemented in VASP,[42] and for these calculations the number of bands was increased to 1,476 (triple the default) for the sum over empty states.AcknowledgementsWe are grateful to the EPSRC for financial support of the project (EP/K004956/1) and the University of Bath for a studentship to JVK. We would also like to thank the Advanced Light Source, Lawrence Berkeley National Laboratory for the beamtime to perform these measurements. The ALS is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The computational modelling was carried out using the Archer HPC facility via the UK Materials Chemistry Consortium, which is supported by the EPSRC under grant no. EP/L000202. Calculations were also carried out using the Balena HPC facility at the University of Bath, which is maintained by Bath University Computing Services.Keywords: Silver ? Structure-property relationships ? SCSC transformation ? Coordination chemistry ? Phenylpyridine[1]a) D. Braga, F. Grepioni, A. G. Orpen in Crystal Engineering: From Molecules and Crystals to Materials, NATO Science Series, Springer-Science, 1999; b) B. Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629-1658; c) K. Biradha, C.-Y. Su, J. J. Vittal, Cryst. Growth Des. 2011, 11, 875-886; d) G. R. Desiraju, Angew. Chem. Int. Ed. 2007, 46, 8342-8356; e) G. R. Desiraju, Angew. Chem. Int. Ed. 1995, 34, 2311-2327.[2]a) J. V. Knichal, W. J. Gee, A. D. Burrows, P. R. Raithby, C. C. Wilson, Cryst. Growth Des. 2015, 15, 465-474; b) E. R. T. Tiekink, J. Zukerman-Schpector in The Importance of Pi-Interactions in Crystal Engineering: Frontiers in Crystal Engineering, John Wiley & Sons, Ltd, Chichester, UK, 2012.[3]M.-C. Hong, L. Chen in Design and Construction of Coordination Polymers, John Wiley & Sons, Inc., New Jersey, 2009.[4]a) G. K. Kole, G. K. Tan, J. J. Vittal, Cryst. Growth Des. 2012, 12, 326-332; b) Q. Chu, D. C, Swenson, L. R. MacGillivray, Angew. Chem. Int. Ed. 2005, 44, 3569-3572; c) M. A. Sinnwell, J. Baltrusaitis, L. R. MacGillivray, Cryst. Growth Des. 2015, 15, 538-541; d) R. Santra, M. Garai, D. Mondal, K. Biradha, Chem. Eur. J. 2013, 19, 489-493; e) S. Samai, P. Ghosh, K. Biradha, Chem. Commun. 2013, 49, 4181-4183; f) H. Schmidbaur, A. Schier, Angew. Chem. Int. Ed. 2015, 54, 746-784.[5]a) S. R. Batten, J. Solid State Chem. 2005, 178, 2475-2479; b) M. Du, X.-H. Bu, Z. Huang, S.-T. Chen, Y.-M. Guo, Inorg. Chem. 2003, 42, 552-559; c) Y.-B. Dong, Y.-Y. Jiang, J. Li, J.-P. Ma, R.-Q. Huang, S. R. Batten, J. Am. Chem. Soc. 2007, 129, 4520-4521; d) Y.-B. Dong, H.-X. Xu, J.-P. Ma, R.-Q. Huang, Inorg. Chem. 2007, 45, 3325-3343.[6]A. V. Aggarwal, A. Thiessen, A. Idelson, D. Kalle, D. Würsch, T. Stangl, F. Steiner, S.-S. Jester, J. Vogelsang, S. H?ger, J. M. Lupton, Nat. Chem. 2013, 5, 964-970.[7]S. C. Rasmussen, S. E. Ronco, D. A. Mlsna, M. A. Billadeau, W. T. Pennington, J. W. Kolis, J. D. Petersen, Inorg. Chem. 1995, 34, 821-829.[8]A. J. Blake, G. Baum, N. R. Champness, S. S. M. Chung, P. A. Cooke, D. Fenske, A. N. Khlobystov, D. A. Lemenovskii, W.-S. Li, M. Schr?der, J. Chem. Soc., Dalton Trans. 2000, 4285-4291.[9]a) S. Suryabhan, K. Rajendran, CrystEngComm 2015, 17, 7363-7371; b) B. Li, S.-Q. Zang, C. Ji, H.-W. Hou, T. C. W. Mak, Cryst. Growth Des. 2012, 12, 1443-1451; c) S.-L. Cai, S.-R. Zheng, J.-B. Tan, M. Pan, J. Fan, W.-G. Zhang, CrystEngComm, 2011, 13, 6345-6348; d) D. Sun, H.-R. Xu, C.-F. Yang, Z.-H. Wei, N. Zhang, R.-B. Huang, L.-S. Zheng, Cryst. Growth Des. 2010, 10, 4642-4649; e) G.-P. Yang, Y.-Y. Wang, P. Liu, A.-Y. Fu, Y.-N. Zhang, J.-C. Jin, Q.-Z. Shi, Cryst. Growth Des. 2010, 10, 1443-1450; f) X.-F. Zheng, L.-G. Zhu, Cryst. Growth Des. 2009, 9, 4407-4414; g) F.-F. Li, J.-F. Ma, S.-Y. Song, J. Yang, H.-Q. Jia, N.-H. Hu, Cryst. Growth Des. 2006, 6, 209-215; h) A. N. Khlobystov, N. R. Champness, C. J. Roberts, S. J. B. Tendler, C. Thompson, M. Schr?der, CrystEngComm, 2002, 4, 426-431.[10]C. Deegan, M. McCann, M. Devereux, B. Coyle, D. A. Egan, Cancer Lett. 2007, 247, 224-233.[11]a) D. R. Monteiro, L. F. Gorup, A. S. Takamiya, A. C. Ruvollo, E. R. de Camargo, D. B. Barbosa, Int. J. Antimicrob. Agents 2009, 34, 103-110; b) B. S. Creaven, D. A. Egan, K. Kavanagh, M. McCann, M. Mahon, A. Nobel, B. Thati, M. Walsh, Polyhedron 2005, 24, 949-957.[12]a) C. Seward, J. Chan, D. Song, S. Wang, Inorg. Chem. 2003, 42, 1112-1120; b) A. Casti?eiras, N. Fernández-Hermida, I. García-Santos, J. L. Pérez-Lustres, I. Rodríguez-González, Dalton Trans., 2012, 41, 3787-3796.[13]a) M. D. Ward, P. R. Raithby, Chem. Soc. Rev. 2013, 42, 1619-1636; b) K. Chainok, S. M. Neville, C. M. Forsyth, W. J. Gee, K. S. Murray, S. R. Batten, CrystEngComm 2012, 14, 3717-3726; c) S. Muthu, J. H. K. Yip, J. J. Vittal, J. Chem. Soc.; Dalton Trans. 2002, 24, 4561-4568; d) A. J. Blake, N. R. Champness, A. N. Khlobystov, D. A. Lemenovskii, W.-S. Li, M. Schr?der, Chem. Commun. 1997, 1339-1340; e) T. M. Garrett, U. Koert, J.-M. Lehn, A. Rigault, D. Meyer, J. Fischer, J. Chem. Soc., Chem. Commun. 1990, 557-558.[14]a) M. B. Duriska, S. R. Batten, D. J. Price, Aus. J. Chem. 2006, 59, 26-29; b) C. Kappenstein, A. Ouali, M. Guerin, J. ?ernak, J. Chromic, Inorg. Chem. Acta 1988, 147, 189-197; c) Y.-P. Ren, L.-S. Long, R.-B. Huang, L.-S. Zheng, Appl. Organomet. Chem. 2005, 19, 1070-1071; d) H.-X. Zhang, Z.-N. Chen. C.-Y. Su, C. Ren, B.-S. Kang, J. Chem. Crystallogr. 1999, 29, 1239-1243.[15]J. V. Knichal, W. J. Gee, A. D. Burrows, P. R. Raithby, S. J. Teat, C. C. Wilson, Chem. Commun. 2014, 50, 14436-14439.[16]I. Persson, K. B. Nilsson, Inorg. Chem. 2006, 45, 7428-7434.[17]A. H. Pakiari, Z. Jamshidi, J. Phys. Chem. A 2010, 114, 9212-9221.[18]A. F. Pedicini, A. C. Reber, S. N. Khanna, J. Chem. Phys. 2013, 139, 164317-164317-8.[19]P. Pyykk?, Chem. Rev., 1997, 97, 597-636.[20]R. A. Coxall, S. G. Harris, D. K. Henderson, S. Parsons, P. A. Tasker, R. E. P. Winpenny, J. Chem. Soc., Dalton Trans. 2000, 2349-2356.[21]A. Bondi, J. Phys. Chem. 1964, 68, 441-451.[22]C. Janiak, J. Chem. Soc., Dalton Trans. 2000, 3885-3896.[23]J. M. Skelton, E. L. da Silva, R. Crespo-Otero, L. E. Hatcher, P. R. Raithby, S. C. Parker, A. Walsh, Faraday Discuss. 2015, 177, 181-202.[24]K. Momma, F. Izumi, J. Appl. Cryst. 2011, 44, 1272-1276.[25]D. A. Atwood, A. R. Hutchison, Y. Zhang in Group 13 Chemistry III, Springer Berlin Heidelberg, Eds. Roesky, H. W.; Atwood, D. A. 2003, 167-201.[26]G.-G. Luo, D. Sun, N. Zhang, R.-B. Huang, L.-S. Zheng, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2009, 65, m377-m381.[27]G. A. Bowmaker, C. Di Nicola, Effendy, J. V. Hanna, P. C. Healy, S. P. King, F. Marchetti, C. Pettinari, W. T. Robinson, B. W. Skelton, A. N. Sobolev, A. Tbcaru, A. H. White, Dalton Trans. 2013, 42, 277-291.[28]C. Y. Chen, J. Y. Zeng, H. M. Lee, Inorg. Chem. Acta, 2007, 360, 21-30.[29]a) G.-M. Wang, J.-H. Li, Z.-X. Li, P. Wang, H. Li, Z. Anorg. Allg. Chem., 2008, 634, 1192-1196. b) G. A. Bowmaker, Effendy, K. C. Lim, B. W. Skelton, D. Sukarianingsih, A. H. White, Inorg. Chim. Acta, 2005, 358, 4342-4370.[30]K. Nilsson, A. Oskarsson, Acta Chem. Scand. A, 1982, 36, 605-610.[31]H. Krautscheid, N. Emig, N. Klaassen, P. Seringer, J. Chem. Soc., Dalton Trans., 1998, 3071-3077.[32]a) H.-N. Adams, W. Hiller, J. Str?hle, Z. Anorg. Allg. Chem., 1982, 485, 81-91. b) W. Conzelmann, W. Hiller, J. Strahle, G. M. Sheldrick, Z. Anorg. Allg. Chem., 1984, 512, 169-176.[33]R. M. Edkins, S. L. Bettington, A. E. Goeta, A. Beeby, Dalton Trans. 2011, 40, 12765-12770.[34]G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112-122.[35]M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G. L. Cascarano, L. De Caro, C. Giacovazzo, G. Polidori, R. Spagna, J. Appl. Cryst. 2005, 38, 381-388.[36]L. J. Barbour, J. Supramol. Chem. 2001, 1, 189-191.[37]O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Puschmann, J. Appl. Cryst. 2009, 42, 339-341.[38]a) J. Heyd, G. E. Scuseria, M. Ernzerhof, J. Chem. Phys. 2003, 118, 8207-8215; b) J. Heyd, G. E.. Scuseria, M. Ernzerhof, J. Chem. Phys. 2006, 124, 219906; c) G. Kresse, J. Hafner, Phys. Rev. B. 1993, 47, 558-561.[39]a) J. P. Perdew, A. Ruzsinszky, G. I. Csonka, O. A. Vydrov, G. E. Scuseria, L. A. Constantin, X. Zhou, K. Burke, Phys. Rev. Lett. 2008, 100, 136406-136406-4; b) J. P. Perdew, A. Ruzsinszky, G. I. Csonka, O. A. Vydrov, G. E. Scuseria, L. A. Constantin, X. Zhou, K. Burke, Phys. Rev. Lett. 2009, 102, 039902.[40]A. V. Krukau, O. A. Vydrov, A. F. Izmaylov, G. E. Scuceria, J. Chem. Phys. 2006, 125, 224106-224106-5.[41]a) P. E. Bl?chl, Phys. Rev. B 1994, 50, 17953-17979; b) G. Kresse, D. Joubert, Phys. Rev. B 1999, 59, 1758-1775.[42]M. Gajdo?, K. Hummer, G. Kresse, J. Furthmüller, F. Bechstedt, Phys. Rev. B 2006, 73, 045112-045112-9. Entry for the Table of Contents (Please choose one layout)FULL PAPERThis work explores the effects of anion variation on silver complexes of 4-(phenylethynyl)pyridine (pep), linking structure with property such as propensity for single-crystal-to-single-crystal (SCSC) transformations. Key Topic*Author(s), Corresponding Author(s)*Page No. – Page No.Title*SCSC Transformations ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download