Anion Photoelectron Spectroscopy and Theoretical Investigation on Nb₂Si_<i>n</i>^–^/0 (<i>n</i> = 2–12) Clusters

Abstract

We measured the photoelectron spectra of Nb2Sin– (n = 2–12) anions and investigated the geometric structures and electronic properties of Nb2Sin– anions and their neutral counterparts with ab initio calculations. The most stable structures of Nb2Sin–/0 (n = 2–12) clusters can be regarded as a central axis of Nb2 surrounded by the Si atoms. The most stable isomers of Nb2Sin– anions are in spin doublet states, while those of the neutral clusters are in spin singlet states. The results showed that the two Nb atoms in Nb2Sin–/0 clusters incline to form a strong Nb–Nb bond and also prefer to occupy the high coordination sites to form more Nb–Si bonds. The most stable isomers of anionic and neutral Nb2Si3 are D3h-symmetric trigonal bipyramid structures, and that of Nb2Si6– has C2h symmetry with the six Si atoms forming a chair-shaped structure. The ground state structure of the Nb2Si12– anion is a C6v-symmetric capped hexagonal antiprism in which one Nb atom is encapsulated inside the Si12 cage and the second Nb atom caps the top of the hexagonal antiprism. It is found that the atomic dipole moment-corrected Hirshfeld population (ADCH) charge distributions on the two Nb atoms not only depend on the electronegativities of Si and Nb atoms but also relate with the structural evolution of Nb2Sin– clusters. The molecular orbital analyses of Nb2Si3–, Nb2Si6–, and Nb2Si12– anions indicate that the delocalized Nb2–Sin ligand interactions and the strong Nb–Nb bonds play important roles in their structural stability.