Gold , four/five coordination

An interesting variation of four versus five coordination is afforded by a series of di-2-pyridyl ketone complexes of Pd(II), Pt(II), and Au(III). The ligand coordinates in chelate fashion via the nitrogens, but protic molecules HX (X = OH, OMe, or OEt) essentially solvate the complex by converting the ketone to a diol form which can then also occupy the apical coordination site. Structure 14 depicts such a hydrated gold(III) species. 

Gold(m) complexes have been obtained by using a chelating diarsine ligand from the reaction with sodium tetrachloroaurate(m) in presence of sodium iodide. The iodide [Au(diars)2I2]I and other cations, [Au(diars)2l]2+ and [Au(diars)2]3 +, can be obtained. It is held that these are species with six, five and four coordination for Au111 with octahedral,33 trigonal bipyramidal and planar structures, respectively. Chelating phosphine complexes also exist. 

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