Structural, spectroscopic and theoretical studies of (^tButyl-isocyanide)gold(I) iodide

The complexes (^tBuNC)AuCl and (^tBuNC)AuI ¹³C-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 4.162 Å, well beyond the sum of the van der Waals radii. It therefore appears that (^tBuNC)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.