Abstract:
The four covalent complexes of nickel (II) fall into two classes (a) the paramagnetic group containing two unpaired electrons and (b) those which are diamagnetic. Whenever X-ray strucural data or electric dipole moments are available the latter have been shown to be square planar. The diamagnetism indicates that one dγ orbital is not used by non-bonding electrons and this orbital together with a 4s and two 4p orbitals gives rise to the Pauling picture of four square planar 3d4s4p2 bonds.
Bivalent Platinum and Palladium form square complexes with great facility; in fact, no paramagnetic complexes of Pt (II) or Pd(II) are known. X-ray analysis has shown the following amine complexes to have the co-planar configuration.
