Various bond interactions between NO and anionic gold clusters: a theoretical calculation.

We studied the electronic and geometrical structures of Au n NO - ( n = 1-20) using the B3LYP method with relatively large basis sets to understand the size-dependent reactivities of Au n - with NO in recent experiments. In most cases, the Au n - in a Au n NO - maintains its original geometries, and NO bonds with one gold atom in the N-atop pattern. The theoretical adsorption energy of NO in an even-sized Au n NO - is generally larger than those in its odd-sized neighbors, which is consistent with the observed even-odd oscillation in experiments. Various bond interactions are identified between Au n - and NO according to analyses on the NO bond lengths, NO stretching frequencies, charge transfer extents, and densities of states of Au n NO - . For the odd-sized Au n NO - in their doublet states, the bonds between Au n - and NO can be described as weak dative bonds in the small size range, or even weaker electrostatic interactions for the large ones. For the even-sized Au n NO - in their triplet states (with the exception of Au 10 NO - and Au 16 NO - ), the electron transfer from Au n - to NO forms a triplet NO - and a neutral Au n , which bind together mainly through electrostatic interactions. The lowest-lying structures of Au 10 NO - and Au 16 NO - are in their singlets, and the bonds between NO and their gold parts can be described as polar covalent bonds. The stabilities of these two exceptional complexes are enhanced by the closed electron shells formed on their gold parts.