Bonding in . . Valence Bond Theory Table . : Number of Orbitals and Types of Hybridisations sp Tetrahedral dsp Square planar sp Trigonal bipyramidal sp Octahedral d sp Octahedral number Type of hybridisation Distribution of hybrid orbitals in space .
Indicate the types of isomerism exhibited by the following complexes and draw the structures for these isomers: (i) K[Cr(H O) (C O ) (ii) [Co(en) ]Cl (iii) [Co(NH ) (NO )](NO ) (iv) [Pt(NH )(H O)Cl ] . Give evidence that [Co(NH ) Cl]SO and [Co(NH ) (SO )]Cl are ionisation isomers. It is usually possible to predict the geometry of a complex from the knowledge of its magnetic behaviour on the basis of the valence bond theory. In the diamagnetic octahedral complex, [Co(NH ) ] + , the cobalt ion is in + oxidation state and has the electronic configuration d .
The hybridisation scheme is as shown in diagram. Orbitals of Co ion sp d hybridised orbitals of Co [CoF ] (outer orbital or high spin complex) Six pairs of electrons from six F ions s p sp d hybrid d Six pairs of electrons, one from each NH molecule, occupy the six hybrid orbitals. Thus, the complex has octahedral geometry and is diamagnetic because of the absence of unpaired electron. In the formation of this complex, since the inner d orbital ( d ) is used in hybridisation, the complex, [Co(NH ) ] + is called an inner orbital or low spin or spin paired complex .
The paramagnetic octahedral complex, [CoF ] – uses outer orbital ( d ) in hybridisation ( sp ). It is thus called outer orbital or high spin or spin free complex . Thus: In tetrahedral complexes one s and three p orbitals are hybridised to form four equivalent orbitals oriented tetrahedrally. This is ill- ustrated