Molecular orbital theory for square planar

A Molecular Orbital Theory for Square Planar Metal Complexes... 

It is the purpose of this paper to develop a molecular orbital theory for square planar metal complexes. Both the spectral and magnetic properties of typical square planar complexes of Ni2+, Pda+, Pts+ and Au8+ will be considered m order to arrive at consistent values for the molecular orbital energies. However, in contrast to previous workers, effort will be concentrated on the assignments of the charge transfer bands of representative square planar complexes. 

Gray HB, Ballhausen CJ (1963) A molecular orbital theory for square planar metal complexes. J Am Chem Soc 85 260... 

Square-planar bis(dithiolene) complexes have also been the subject of theoretical investigations (43-46). For example, density functional theory (DFT) calculations indicated that the highest occupied molecular orbital (HOMO) for Ni(S2C2H2)2 is primarily a ligand-based orbital comprising of four 3pz orbitals of sulfur, perpendicular to the molecular xy plane, and four 2p-orbitals of carbon with opposite phases. The lowest unoccupied molecular orbital (LUMO) is a mix of ligand-metal orbitals, but still mostly of the ligand... 

The result here is quite satisfactory because XeF4 does in fact exhibit square planar geometry. It is worth noting, however, that a square planar shape for XeF4 is also predicted by VSEPR theory. Despite the fact that the molecular orbital method has made some inroads as of late, VSEPR is still the best approach available for rationalizing the molecular geometries of noble gas compounds. 

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