Noble gas-metal chemical bonds. Microwave spectra, geometries, and nuclearquadrupole 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 complex es have been found to be linear and are relatively rigid in their ground vi brational states. The noble gas-gold stretching frequencies have been estim ated to be 198 and 161 cm(-1) for Ar-AuCl and Kr-AuCl, respectively. From t he isotopic data obtained. ro structures have been calculated for both Ar-A uCl and Kr-AuCl, while a partial substitution (r(s)) structure has been obt ained for Kr-AuCl. The Ar-Au distance has been found to be 2.47 Angstrom, w hile 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 ener gies 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 fou nd 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 energ ies, indicates that the Ar-Au and Kr-Au bonds are weakly covalent.