Size-Dependent Association of Cobalt Deuteride Cluster Anions Co3Dn- (n = 0-4) with Dinitrogen.

Dinitrogen (N2) activation by metal hydride species is of fundamental interest and practical importance while the role of hydrogen in N2 activation is not well studied. Herein, the structures of Co3Dn- (n = 0-4) clusters and their reactions with N2 have been studied by using a combined experimental and computational approach. The mass spectrometry experiments identified that the Co3Dn- (n = 2-4) clusters could adsorb N2 while the Co3Dn- (n = 0 and 1) clusters were inert. The photoelectron imaging spectroscopy indicated that the electron detachment energies of Co3D2-4- are smaller than those of Co3D0,1-, which characterized that it is easier to transfer electrons from Co3D2-4- than from Co3D0,1- to activate N2. The density functional theory calculations generally supported the experimental observations. Further analysis revealed that the H atoms in the Co3Hn- (n = 2-4) clusters generally result in higher energies of the Co 3d orbitals in comparison with the Co3Hn- (n = 0 and 1) systems. By forming chemical bonds with H atoms, the Co atoms of Co3H2-4- are less negatively charged with respect to the naked Co3- system, which leads to higher N2 binding energies of Co3H2-4N2- than that of Co3N2-.