Four-coordinate gold complexes

Uson, R., Laguna, A., Vicente, J., Garcia, J., Jones, P.G. and Sheldrick, G.M. (1981) Preparation of three- and four-coordinate gold(I) complexes crystal structure of bis [o-phenylenebis(dimethylarsine)]gold(I) bis(pentafluorophenyl)aurate. Journal of the Chemical Society, Dalton Transactions, (2), 655-657. 

Gimeno, M.C. Laguna. A. Three- and four-coordinate gold(I) complexes. Chem. Rev. 1997, 97. 511. 

Gold compounds are known in the (-1), (I), (II), (III), and (V) oxidation states. The linearly two-coordinate gold(I) and square planar four-coordinate gold(III) complexes are the most common. 

Gold Compounds. The chemistry of nonmetallic gold is predominandy that of Au(I) and Au(III) compounds and complexes. In the former, coordination number two and linear stereochemistry are most common. The majority of known Au(III) compounds are four coordinate and have square planar configurations. In both of these common oxidation states, gold preferably bonds to large polarizable ligands and, therefore, is termed a class b metal or soft acid. 

Although in most of the above reports structural information is based on X-ray data, Au Mossbauer spectroscopy has also been successfully employed for the investigation of two-, three-, and four-coordination in gold(I) complexes.2551 An increase in coordination numbers leads to a decrease in the isomer shift (IS) by 1-2mm s 1 (three-coordination) or 2-4mm s 1 (four-coordination) relative to two-coordination. For the same ligands, the quadrupole splitting (QS) for three-coordinated complexes is expected to be very similar to that for the two-coordinate derivatives, while that for complexes with Td symmetry should be zero. 

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