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The complexes ( t BuNC)AuCl and ( t BuNC)AuI 13 C-labeled at the isocyanide group were prepared and investigated by concentration-and temperature-dependent IR and NMR spectroscopy in dichloromethane solution. No indication for association of the molecules was obtained. The crystal structure of the iodide complex was determined by X-ray diffraction methods and shown to feature only monomers with extremely large intermolecular Au-Au contacts of 4.162Å, well beyond the sum of the van der Waals radii. It therefore appears that ( t BuNC)AuI is a rare example of a sterically non-hindered L-Au-X complex which shows no aurophilic interactions whatsoever. In a quantum-chemical analysis (at the local MP2 level) of the dimerization of the model compounds (MeNC)AuCl and (MeNC)AuI in various dimer geometries it was demonstrated that the energy-balance of the dimerization is very delicate and not dominated solely by contributions from correlation / relativistic (aurophilic) effects.

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Trimethylphosphine)gold() nitrate was prepared from the reaction of (Me 3 P)AuCl and AgNO 3 in MeOH-CH 2 Cl 2 . Single crystals from CH 2 Cl 2 -pentane contain trimers [(Me 3 P)Au(ONO 2 )] 3 as sub-units of polymeric chains. The organization is based on short aurophilic Au-Au contacts. A discussion considering all other known (Me 3 P)AuX structures leads to the conclusion that small, electronegative anions X favour aurophilic multi-coordination with longer Au ؒ ؒ ؒ Au contacts, while less electronegative, bulky groups X induce dimerization with short Au ؒ ؒ ؒ Au contacts. In all cases neighbouring molecules are arranged with their principal axes roughly perpendicular (staggered). Crystals of ( t BuNC)Au(ONO 2 ) grown from CH 2 Cl 2 -pentane at Ϫ25 ЊC were shown to be a 2 : 1 dichloromethane solvate with a new meander-type structure, which is stable only at low temperature and under the standard pressure of a dichloromethane atmosphere. The structure is based on aurophilic interactions of a similar nature as in the solvent-free phase (obtained at 5 ЊC) as judged from the bond distance parameters, but the solvent molecules are accommodated in cavities formed through a different puckering of the chains. A comparison with other structures of (RNC)AuX molecules suggests that the parallel (eclipsed) head-to-tail alignment of the molecules is the preferred organization in the absence of other structure-determining effects.