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The nature of the chemical bond between gold and the noble gases in the simplest prototype of Au(l) complexes (NgAuF and NgAu+, where Ng = Ar, Kr, Xe), has been theoretically investigated by state of art all-electron fully relativistic DC-CCSD(T) and DFT calculations with extended basis sets. The main properties of the molecules, including dipole moments and polarizabilities, have been computed and a detailed study of the electron density changes upon formation of the Ng-Au bond has been made. The Ar-Au dissociation energy is found to be nearly the same in both Argon compounds. It almost doubles along the NgAuF series and nearly triples in the corresponding NgAu+ series. The formation of the Ng- Au(I) bonds is accompanied by a large and very complex charge redistribution pattern which not only affects the outer valence region but reaches deep into the core-electron region. The charge transfer from the noble gas to Au taking place in the NgAu+ systems is largely reduced in the fluorides but the Ng-Au chemical bond in the latter systems is found to be tighter near the equilibrium distance. The density difference analysis shows, for all three noble gases, a qualitatively identical nature of the Ng-Au bond, characterized by the pronounced charge accumulation in the middle of the Ng-Au internuclear region which is typical of a covalent bond. This bonding density accumulation is more pronounced in the fluorides, where the Au-F bond is found to become more ionic, while the overall density deformation is more evident and less localized in the NgAU+ systems. Accurate density difference maps and charge-transfer curves help explain very subtle features of the chemistry of Au(l), including its peculiar preference for tight linear bicordination. [ABSTRACT FROM AUTHOR]

The gas-phase infrared spectra of discrete uranyl ([UO2]2+) complexes ligated with acetone and/or acetonitrile were used to evaluate systematic trends of ligation on the position of the OUO stretch and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric OUO stretching frequency was measured at 1017 cm-1 for [UO2(CH3COCH3)2]2+ and was systematically red shifted to 1000 and 988 cm-1 by the addition of a third and fourth acetone ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from two to four and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO2(CH3CN)n]2+ complexes, although the uranyl asymmetric stretching frequencies were greater than those measured for acetone complexes having equivalent coordination, which is consistent with the fact that acetonitrile is a weaker nucleophile than is acetone. This conclusion was confirmed by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3–6 cm-1. [ABSTRACT FROM AUTHOR]