Gold in Oxidation State

As early as 1943, Sommer (101) reported the existence of a stoichiometric compound CsAu, exhibiting nonmetallic properties. Later reports (53, 102, 103,123) confirmed its existence and described the crystal structure, as well as the electrical and optical properties of this compound. The lattice constant of its CsCl-type structure is reported (103) to be 4.263 0.001 A. Band structure calculations are consistent with observed experimental results that the material is a semiconductor with a band gap of 2.6 eV (102). The phase diagram of the Cs-Au system shows the existence of a discrete CsAu phase (32) of melting point 590°C and a very narrow range of homogeneity (42). 

Ultraviolet photoemission spectra have also been used to investigate the electronic band structure of solid CsAu. The apparent spin-orbit 

Evaluation of intensities of X-ray diffraction patterns indicates that the CsCl structure is well ordered in crystalline CsAu. Excess Cs, which is the primary source for conduction electrons, is dispersed in the lattice with increase of the cell parameter (105). Cesium-133 NMR measurements (line shapes, Knight shifts, and relaxation times) confirm this result (105). The interpretation of the data for RbAu is less straightforward, however. 

Recent mass spectral studies confirm the presence of CsAu molecules in the gas phase. From the appearance potentials and the slope of the ionization curve, a dissociation energy of 460 kJ mol-1 was deduced, which agrees well with predicted values for a largely ionic bond. It is also very similar to the value arrived at for CsCl, 444 kJ mol-1 (19a). 

More recently, Peer and Lagowski (75) presented spectroscopic and electrochemical evidence for the existence of Au- ions in liquid ammonia. This is the only example of a transition metal anion in any solvent. In a simple yet elegant technique, the solutions of auride ion, Au, could be prepared by the dissolution of metallic gold in ammonia 

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For gold in oxidation states other than III, see H. ScHMiDBAUR and K. C. Dash, Adv. Inorg, Chem. 25, 239-66 (1982). 

It is dissolved by aqua regia (a mixture of concentrated hydrochloric and nitric acids). The product here is chlorauricil 11) acid, HAUCI4 in the complex chloraurate ion [AuClJ gold is in oxidation state + 3, auric gold. ... 

The destabilization of the 5d orbitals allows the easy formation of the oxidation state III in gold to be explained this is almost absent in silver and the stabilization of the 6s orbitals explains the formation of the gold(-I), oxidation state, which is unknown in silver. 

Compounds in oxidation states —I through V are known. The conunon and stable oxidation states that dominate the aqueous chemistry of gold are Au(I) and Au(III). The aquated ions are unstable to reduction, but many complexes are stabihzed by a variety of soft hgands. The remaining oxidation states (—1, II, IV, V) exhibit interesting chemical and physicochemical properties, but have not yet found medicinal applications. 

In addition to the protein complexes of copper ions, CD spectroscopy has also been used to study metal-protein complex formation of the other Group 11 metals, silver, and gold. The Ag+ ion has been used extensively in metal-protein experiments to act as an analog of Cu+ complex formation. Ag+ is comparable to Cu+ in oxidation state, the types of hgands to which it binds, and often displays equivalent binding geometries to these hgands. Moreover, Ag+ is easier... 

The data strongly suggest that Au is in oxidation state +1 and that the bis-triphenylmethylenephosphorane-gold has the structure given by 4. However, the distinction between Cls peaks for normal carbon (285.0 eV) and for carbanion carbon (283.8 eV) was difficult due to a 18 1 intensity ratio between the two. Therefore, Yamamoto and Konno measured XPS spectra of another yhde-gold complex, namely bis(dimethylsulfoxonium methyhde)gold19b, where the intensity ratio between normal... 

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