the metal and the ligand. . The hybridised orbitals are directional and their orientation in space gives a definite geometry to the complex ion. Coordination number Hybridisation Geometry Examples sp Linear [CuCl ] - , [Ag(CN) ] - sp Trigonal planar [HgI ] - sp Tetrahedral [Ni(CO) ], [NiCl ] - dsp Square planar [Ni(CN) ] - , [Pt(NH ) ] + dsp ( dx2-y2 orbital is involved ) Trigonal bipyramidal [Fe(CO) ] d sp ( dz2 and dx2-y2 orbitals of inner shell are involved ) Octahedral [Ti(H O) ] + , [Fe(CN) ] - , [Fe(CN) ] - , [Co(NH ) ] + (Inner orbital complexes) sp d ( dz2 and dx2-y2 orbitals of the outer shell are involved) Octahedral [FeF ] - ,[CoF ] - , [Fe(H O) ] + (Outer orbital complexes) .
In the octahedral complexes, if the (n- ) d orbitals are involved in hybridisation, then they are called inner orbital complexes or low spin complexes or spin paired complexes. If the nd orbitals are involved in hybridisation, then such complexes are called outer orbital or high spin or spin free complexes. Here n represents the principal quantum number of the outermost shell. .
The complexes containing a central metal atom with unpaired electron(s) are paramagnetic. If all the electrons are paired, then the complexes will be diamagnetic. XII U5 Coordination XII U5 Coordination - - - - . Ligands such as CO, CN - , en, and NH present in the complexes cause pairing of electrons present in the central metal atom.
Such ligands are called strong field ligands. . Greater the overlapping between the ligand orbitals and the hybridised metal orbital, greater is the bond strength. Let us illustrate the VBT by considering the following examples.
Illustration Complex [Ni(CO) ] Central metal atom and its outer electronic configuration Ni: 3d , 4s Outer orbitals of