![[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)](https://image.slidesharecdn.com/lec3-230210194434-0730f8fd/85/Lec3-pdf-4-320.jpg)
![Factors Affecting the Magnitude of Δ
1. Higher oxidation states of the metal atom correspond to larger Δ.
Δ =10,200 cm-1 for [CoII(NH3)6]2+ and 22,870 cm-1 for [CoIII(NH3)6]3+
Δ =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 Δ.
For hexaammine complexes [MIII(NH3)6]3+:
Δ 22 870 1 (C )
Δ = 22,870 cm-1 (Co)
34,100 cm-1 (Rh)
41,200 cm-1 (Ir)
3. Geometry of the metal coordination unit affects Δ greatly.
Tetrahedral complexes ML4 have smaller Δ than octahedral ones ML6:
Δ = 10,200 cm-1 for [CoII(NH3)6]2+
5,900 cm-1 for [CoII(NH3)4]2+
4. Nature of the ligands.
For [CoIIIL ] Δ in cm-1: 13 100 (F-); 20 760 (H O); 22 870 (NH )
For [Co L6], Δ in cm : 13,100 (F ); 20,760 (H2O); 22,870 (NH3)
For [CrIIIL6], Δ in cm-1: 15,060 (F-); 17,400 (H2O); 26,600 (CN-)](https://image.slidesharecdn.com/lec3-230210194434-0730f8fd/85/Lec3-pdf-5-320.jpg)
![Distribution of Electrons in a Tetrahedral Complex
T t h d l litti i ld l h t lt i i i f th l t
Tetrahedral splitting is seldom large enough to result in pairing of the electrons.
As a result, low-spin tetrahedral complexes are not common.
A rare example is Cr[N(SiMe3)2]3[NO]
d1 e1 t2
0 0.6 Δt
d2 e2 t2
0 1.2 Δt
d3 e2 t2
1 0.8 Δt
d4 e2 t2
2 0.4 Δt
d5 e2 t2
3 0 0 Δt
d e t2 0.0 Δt
d6 e3 t2
3 0.6 Δt
d7 e4 t2
3 1.2 Δt
d8 e4 t2
4 0.8 Δt
d9 e4 t2
5 0.4 Δt
d10 e4 t2
6 0.0 Δt
2 t](https://image.slidesharecdn.com/lec3-230210194434-0730f8fd/85/Lec3-pdf-11-320.jpg)
![When to Expect Square Planar Geometry
In the case of d8 metals and strong ligands:
Ni2+, in the presence of strong field ligands such as CN- forms a square planar complex.
2nd and 3rd row d8 metals form square planar geometry irrespective of the nature of the
ligand:
With Pd2+ (which already generates a strong field) even a weak field ligand such as Cl-
l d t th f ti f l l f l [PdCl ]2
leads to the formation of a square planar complex, for example, [PdCl4]2-.](https://image.slidesharecdn.com/lec3-230210194434-0730f8fd/85/Lec3-pdf-14-320.jpg)
Lec3.pdf
- 1. Crystal Field Splitting in an Octahedral Field eg Energy 3/5 o o t2g 2/5 o eg - The higher energy set of orbitals (dz2 and dx2-y2) t2g - The lower energy set of orbitals (dxy, dyz and dxz) Δo or 10 Dq - The energy separation between the two levels The e orbitals are repelled by an amount of 0 6 Δ The eg orbitals are repelled by an amount of 0.6 Δo The t2g orbitals to be stabilized to the extent of 0.4 Δo.
- 2. Tetrahedral Field t2 2/5 Energy 2/5 t t e 3/5 t The higher energy set of orbitals (dxz, dyz, dxy) is labeled as t2 and the lower energy set (dz2 and dx2-y2) is labeled 2 gy ( z x y ) 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 Δ = 4/9 Δ field. For most purposes the relationship may be represented as Δt = 4/9 Δo
- 4. [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)
- 5. Factors Affecting the Magnitude of Δ 1. Higher oxidation states of the metal atom correspond to larger Δ. Δ =10,200 cm-1 for [CoII(NH3)6]2+ and 22,870 cm-1 for [CoIII(NH3)6]3+ Δ =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 Δ. For hexaammine complexes [MIII(NH3)6]3+: Δ 22 870 1 (C ) Δ = 22,870 cm-1 (Co) 34,100 cm-1 (Rh) 41,200 cm-1 (Ir) 3. Geometry of the metal coordination unit affects Δ greatly. Tetrahedral complexes ML4 have smaller Δ than octahedral ones ML6: Δ = 10,200 cm-1 for [CoII(NH3)6]2+ 5,900 cm-1 for [CoII(NH3)4]2+ 4. Nature of the ligands. For [CoIIIL ] Δ in cm-1: 13 100 (F-); 20 760 (H O); 22 870 (NH ) For [Co L6], Δ in cm : 13,100 (F ); 20,760 (H2O); 22,870 (NH3) For [CrIIIL6], Δ in cm-1: 15,060 (F-); 17,400 (H2O); 26,600 (CN-)
- 6. Spectrochemical Series An arrangement of ligands according to their ability to increase Δ for a given metal center Weak – I-, Br-, SCN-, Cl-, N3 -, F-, H2NC(O)NH2, OH-, ox2-, O2-, H2O, NCS-, py, NH3, en , bpy, phen, NO2 -, CH3 -, C6H5 -, CN-, CO – Strong Strong Field (Ligand) Weak Field Field (Ligand)
- 7. Distribution of Electrons in an Octahedral Complex d1 d2 d3 Strong field Weak field Strong field Weak field Strong field Weak field d1 d2 d3 Net energy decrease is called crystal field stabilization energy (CFSE) For d1, CFSE = 1 × 0.4 = 0.4 Δo For d , CFSE 1 0.4 0.4 Δo For d2, CFSE = 2 × 0.4 = 0.8 Δo For d3, CFSE = 3 × 0.4 = 1.2 Δo o
- 8. Distribution of Electrons in an Octahedral Complex d4 There are two possibilities for metal ions having d4-d7 electronic configuration. Depending on the nature of the ligands and the metal they could be high-spin or low- i l 2 spin complexes. 2 u.e. 4 u.e. For the d4 system, CFSE = For high-spin, (3 × 0.4) – (1 × 0.6) = 0.6 Δo and g p ( ) ( ) o for low-spin, 4 × 0.4 = 1.6 Δo 2.0 Δo 2.4 Δo 1.8 Δo 0.0 Δo 0.4 Δo 0.8 Δo d5 d6 d7 1 u.e. 5 u.e. 0 u.e. 4 u.e. 1 u.e. 3 u.e.
- 9. Distribution of Electrons in an Octahedral Complex d8 d9 d10 2 u.e. 2 u.e. 1 u.e. 1 u.e. 0 u.e. 0 u.e. For d8, CFSE = (6 × 0.4) – (2 × 0.6) = 1.2 Δo For d , CFSE (6 0.4) (2 0.6) 1.2 Δo For d9, CFSE = (6 × 0.4) – (3 × 0.6) = 0.6 Δo For d10, CFSE = (6 × 0.4) – (4 × 0.6) = 0.0 Δo Metal ions with 4 7 electrons in the d orbital can exist as high spin or low spin In all electronic configurations involving two electrons in the same orbital, the actual CFSE is reduced by the energy spent on pairing the electrons. Metal ions with 4 – 7 electrons in the d orbital can exist as high-spin or low-spin complexes. Weaker ligands tend to give high-spin complexes, whereas stronger ligands tend to give low-spin complexes.
- 10. Distribution of Electrons in an Octahedral Complex d1 t2g 1eg 0 0.4 Δo t2g 1eg 0 0.4 Δo High-spin Low-spin d t2g eg 0.4 Δo t2g eg 0.4 Δo d2 t2g 2eg 0 0.8 Δo t2g 2eg 0 0.8 Δo d3 t2g 3eg 0 1.2 Δo t2g 3eg 0 1.2 Δo d4 3 1 4 0 d4 t2g 3eg 1 0.6 Δo t2g 4eg 0 1.6 Δo d5 t2g 3eg 2 0.0 Δo t2g 5eg 0 2.0 Δo d6 t2g 4eg 2 0.4 Δo t2g 6eg 0 2.4 Δo 2g g o 2g g o d7 t2g 5eg 2 0.8 Δo t2g 6eg 1 1.8 Δo d8 t2g 6eg 2 1.2 Δo t2g 6eg 2 1.2 Δo d9 t 6 3 0 6 Δ t 6 3 0 6 Δ d9 t2g 6eg 3 0.6 Δo t2g 6eg 3 0.6 Δo d10 t2g 6eg 4 0.0 Δo t2g 6eg 4 0.0 Δo
- 11. Distribution of Electrons in a Tetrahedral Complex T t h d l litti i ld l h t lt i i i f th l t Tetrahedral splitting is seldom large enough to result in pairing of the electrons. As a result, low-spin tetrahedral complexes are not common. A rare example is Cr[N(SiMe3)2]3[NO] d1 e1 t2 0 0.6 Δt d2 e2 t2 0 1.2 Δt d3 e2 t2 1 0.8 Δt d4 e2 t2 2 0.4 Δt d5 e2 t2 3 0 0 Δt d e t2 0.0 Δt d6 e3 t2 3 0.6 Δt d7 e4 t2 3 1.2 Δt d8 e4 t2 4 0.8 Δt d9 e4 t2 5 0.4 Δt d10 e4 t2 6 0.0 Δt 2 t
- 12. When to Expect Tetrahedral Geometry If ligands are large; so as to avoid ligand-ligand repulsion If ligands are large; so as to avoid ligand ligand repulsion In case of metal ions with zero CFSE (d0, d5 and d10) or MnO4 - (d0), FeCl4 - (d5, h.s.), ZnCl4 2- (d10) 4 ( ) 4 ( ) 4 ( ) In case of metal ions with small CFSE (d2 and d7) CoCl4 2- (d7, h.s.) – 0.8 Δo vs 1.2 Δt
- 13. Square Planar Field Ligands along the Z axis are removed from axis are removed from an octahedral complex to get a square planar complex Energy
- 14. When to Expect Square Planar Geometry In the case of d8 metals and strong ligands: Ni2+, in the presence of strong field ligands such as CN- forms a square planar complex. 2nd and 3rd row d8 metals form square planar geometry irrespective of the nature of the ligand: With Pd2+ (which already generates a strong field) even a weak field ligand such as Cl- l d t th f ti f l l f l [PdCl ]2 leads to the formation of a square planar complex, for example, [PdCl4]2-.