Noble gas-metal chemical bonds. Microwave spectra, geometries, and nuclear quadrupole coupling constants of Ar-AuCl and Kr-AuCl

The pure rotational spectra of Ar-AuCl and Kr-AuCl have been measured using a pulsed-jet cavity Fourier transform microwave spectrometer. Both complexes have been found to be linear and are relatively rigid in their ground vibrational states. The noble gas-gold stretching frequencies have been estimated to be 198 and 161 cm(-1) for Ar-AuCl and Kr-AuCl, respectively. From the isotopic data obtained. ro structures have been calculated for both Ar-AuCl and Kr-AuCl, while a partial substitution (r(s)) structure has been obtained for Kr-AuCl. The Ar-Au distance has been found to be 2.47 Angstrom, while the Kr-Au distance is 2.52 Angstrom. Ab initio calculations have been performed at the MP2 level of theory on both complexes to obtain geometries, vibrational frequencies, and dissociation energies. The dissociation energies for Ar-AuCl and Kr-AuCl have been estimated to be 47 and 71 kJ mol(-1), respectively. The nuclear quadrupole coupling constant of Au has been found to change significantly on complex formation (to -259.8 MHz in Ar-AuCl, and -349.9 MHz in Kr-AuCl) from its value in the monomer unit (+9.6 MHz in AuCl), which is consistent with extensive charge rearrangement on formation of the complexes. This, in conjunction with the sizable dissociation energies, indicates that the Ar-Au and Kr-Au bonds are weakly covalent.