Reactivity of Tantalum Carbide Cluster Anions TaC ( n = 1-4) with Dinitrogen.

Dinitrogen activation/fixation is one of the most important and challenging subjects in synthetic as well as theoretical chemistry. In this study, the adsorption reactions of N onto TaC ( n = 1-4) cluster anions have been investigated by means of mass spectrometry in conjunction with density functional theory calculations. Following the experimental results that only TaC was observed to adsorb N, theoretical calculations predicted that the TaC reaction system (TaC + N ? TaCN) has a negligible barrier on the approach of N molecule while insurmountable barriers are located on the reaction pathways of TaC/N reaction systems. The natural bond orbital and molecular orbital analysis indicated that the more positive charge on the metal center of TaC would facilitate the initial approach of the nonpolar N molecule, and the appropriate frontier orbital of TaC with proper symmetry (?-type 5d orbital) which can match up well with the ?* antibonding orbital of the N molecule with less ? repulsion and more possibility for ? back-donation would be helpful for the formation of the stable encounter complexes. This study reveals the fundamental rules and key factors governing the N adsorption.