Ligands polarizability

Late transition metals are found on the right of the Periodic Table (e.g. Ni, Pd, Pt, Co, Fe, Ru, Rh, Cu active in low oxidation states) and are more tolerant of oxygen functionalities in the monomer and the polymer. This behavior stems from the preference of late transition metals for soft ligands (polarizable ligands, typically... 

In a tetrahedral complex [ML4] the potential of the electric quadrupole moment 0xy of the metal ion transition produces a constructive correlation of the z-compo-nent of the electric dipole induced in each of the four ligands, proportional to the ligand polarizability, a(L) (Fig. 4). For the case of the cobalt(II) complexes, [60X4] , the X- and the y-component of ligand-induced dipole are analogously aligned constructively by the field of the respective electric quadrupole components Sy and B x. 

Dipole Alignment Effects Ligand Polarizability Effects Chelation... 

M. F. Reid and F. S. Richardson, Anisotropic ligand polarizability contributions to lanthanide 4/ i—> 4/ intensity parameters, Chemical Physics Letters, 95, 501-506 (1983). 

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