Noble gas-metal chemical bonding: the microwave spectra, structures and hyperfine constants of Ar-AuF and Ar-AuBr

The rotational spectra of the complexes Ar-AuF and Ar-AuBr have been observed in the frequency range 7-22 GHz using a pulsed-jet cavity Fourier transform microwave spectrometer. Both complexes are linear and rather rigid in the ground vibrational state, with the Ar-Au stretching frequency estimated as similar to 200 cm(-1). Isotopic data have been used to calculate an r(0) structure for Ar-AuBr while for Ar-AuF only an estimation of the r(0) geometry could be made. Ab initio calculations at the MP2 level of theory model the geometries and stretching frequencies well and predict an Ar-Au bond energy in Ar-AuF of similar to 60 kJ mol(-1). The Au nuclear quadrupole coupling constant changes significantly on complex formation, indicating extensive charge arrangement. This in conjunction with the large dissociation energy and ab initio results show that the Ar-Au bonds in these complexes are weakly covalent in nature.