Dr. Pandit Khakre Asst. Prof Mrs. K.S.K. College, Beed.

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Dr. Pandit Khakre Asst. Prof Mrs. K.S.K. College, Beed

Limitations of VBT : Octahedral d2Sp3 or Sp3.d2 hybridisation tetrahedral & square planner complex. The outer orbital octahedral & tetrahydral complxes of all the ions viz d1 to d10. They must be quantitative conection between spectra & magnetic moment. The splitting of d-orbitals of the central metal ion. Octahedral complexes Co2+ in both cases promotion of a non-bonding d-electron to some higher energy level. Valance bond theory can not be explain reaction rates & mechanism of reaction.

Crystal field theory : H.Brethe & Van Vleck in 1935 is advanced the crystal field theory. This theory is on more useful in explaining the bonding & properties of co-ordination complex. A central metal ion & its ligands arises from electrostatic interaction. The point di poles or simply di pols ligands are dipolar. Ex. NH3 & H2O etc. They have polarised by the positive charge of the cation. The CFT regards the ligand atoms of negative regions or dipoles. Those complete which are having central metal ion. The dipolar ligands with partially filled d orbitals.

Crystal field splitting in ocahedral complexes : The octahedral complex the co-ordination number is 6. The central metal ion is the centre & ligands, occupy the six corners of the octahedraon. In an octahedral complex the dx2-y2 & dz3 are designated as eg orbitals. Octahedral complexes five d-orbitals spilt up into two sets. Higher energy eg orbitals of lower energy tzg. All the ligans is uniformly affecting the electron in the d-orbitals of the metal ion. The energy difference between t2 & eg orbitals 0 Parameter Dq by convention 0 is equl to 10 Dq. Energy of the t2g orbitals is 4Dq or 0. less than the energy. The energy of the eg orbitals is 6Dq or 0.6.

Crystal field spiltting in Tetrahedral complexes : The co ordination number for tetrahedral complex is four. Tetrahedral structure none of the d-orbitals points exactly the ligands. The three d-orbitals dxy, dyz & dzx pointing close to the direction in which ligands are approaching two orbitals. Dx2-y2 & dz2 lying in between the ligand. The three orbitals dxy, dyz & dzx are designated as tz orbitals to have higher energy. The two orbitals dx2-y2 & dz2 are designated as e-orbitals. The e orbitals is stabilized by 6Dq. t2 orbitals is destabilized by 4Dq. The d3 system low spin & high spin states are possible.

The spiltting of d orbitals in tetragonal & square planer The ligands the xy plane tend to approach the contral ion more closely the electrons in d-orbitals. The increase in the energy of dx2-y2 & dxy orbitals in tetragonal complex. The two ligands on z-axis is increased from the d orbitals i.e. dz2, dxz & dyz experiences less repulsion from the ligands than in octahedral geometry. The ligands the order of energy of d orbitals. This as accompained by a further rise in the energles of dx2-y2 & dxy orbitals. The order of energy of different orbitals dy2 = dzx < dz2 < dxy < dx2 – y2

Factors affecting the crystal field parameters : Nature of the ligands Oxidation state of the metal ion Size of d orbitals. Geometry of the complex.