Relationships between Valence Orbital Binding Energies and Crystal Structures in Compounds of Copper, Silver, Gold, Zinc, Cadmium, and Mercury

Theoretical calculations and X-ray spectral data are used to determine the relative binding energies of the Cu, Ag, Au, Zn, Cd, and Hg d orbitals and the ligand p orbitals in the metal chlorides and sulfides. Compared to the S 3p nonbonding orbitals, the metal d orbitals are of lower binding energy for Cu, of slightly higher binding energy for Au, Ag, and Hg, and of considerably higher binding energy for Zn and Cd. Transformation from gaseous monomer to gaseous polymer to condensed phase is shown to raise the metal (M) d orbital energy with respect to the ligand (L) p, resulting in a larger L p-M d energy separation and smaller L p-M d covalent mixing for Cu compounds and a smaller separation and greater covalent mixing for compounds of the other metals. The existence or nonexistence of different oxidation states of these metals in combination with various ligands can be qualitatively understood on the basis of the energies of predominantly M d and L p orbitals obtained from spectra or molecular cluster calculations (and to some extent from the M d and L p atomic orbital energies). Similarly, the coordination numbers and polyhedral distortions in the most stable polymorphs of these compounds are determined by the numbers of M d electrons and the extent of M d-L p covalent mixing. The adoption of structures with low M coordination numbers by compounds with filled M d shells and small M d-L p energy differences serves to lower the M d energy and reduce the destabilization due to M d-L p covalent mixing.