Crystal Field Splitting in an Octahedral Field

Crystal Field Splitting in an Octahedral Field

eg

Energy

3/5 o 2/5 o

o

t2g

eg - The higher energy set of orbitals (dz2 and dx2-y2) t2g - The lower energy set of orbitals (dxy, dyz and dxz)

o or 10 Dq - The energy separation between the two levels

The eg orbitals are repelled by an amount of 0.6 o The t2g orbitals to be stabilized to the extent of 0.4 o.

Energy

Tetrahedral Field

2/5 t 3/5 t

t2

t

e

The higher energy set of orbitals (dxz, dyz, dxy) is labeled as t2 and the lower energy set (dz2 and dx2-y2) is labeled as e.

The crystal field splitting in the tetrahedral field is intrinsically smaller than in the octahedral field. For most purposes the relationship may be represented as t = 4/9 o

Octahedral Vs Tetrahedral

Energy

[Ti(H2O)6]3+ ? a d1 system

The single electron in the t2g orbitals absorb energy in the form of light and gets excited to the eg orbitals. In case of [Ti(H2O)6]3+, this corresponds to 520 nm (20,300 cm-1).

520 nm (243 kJ/mol)

Factors Affecting the Magnitude of

1. Higher oxidation states of the metal atom correspond to larger . =10,200 cm-1 for [CoII(NH3)6]2+ and 22,870 cm-1 for [CoIII(NH3)6]3+ =32,200 cm-1 for [FeII(CN)6]4- and 35,000 cm-1 for [FeIII(CN)6]3-

2. In groups, heavier analogues have larger .

For hexaammine complexes [MIII(NH3)6]3+:

=

22,870 cm-1 (Co)

34,100 cm-1 (Rh)

41,200 cm-1 (Ir)

3. Geometry of the metal coordination unit affects greatly.

Tetrahedral complexes ML4 have smaller than octahedral ones ML6:

=

10,200 cm-1 for [CoII(NH3)6]2+

5,900 cm-1 for [CoII(NH3)4]2+

4. Nature of the ligands.

For [CoIIIL6], in cm-1: 13,100 (F-); 20,760 (H2O); 22,870 (NH3) For [CrIIIL6], in cm-1: 15,060 (F-); 17,400 (H2O); 26,600 (CN-)

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