The structural and electronic properties of NbSin-/0 (n=3-12) clusters: anion photoelectron spectroscopy and ab initio calculations

Niobium-doped silicon clusters, NbSin- (n = 3-12), were generated by laser vaporization and investigated by anion photoelectron spectroscopy. The structures and electronic properties of NbSin- anions and their neutral counterparts were investigated with ab initio calculations and compared with the experimental results. It is found that the Nb atom in NbSin-/0 prefers to occupy the high coordination sites to form more Nb-Si bonds. The most stable structures of NbSi3-7-/0 are all exohedral structures with the Nb atom face-capping the Si-n frameworks. At n = 8, both the anion and neutral adopt a boat-shaped structure and the openings of the boat-shaped structures remain unclosed in NbSi9-10-/0 clusters. The most stable structure of the NbSi11- anion is endohedral, while that of neutral NbSi11 is exohedral. The global minima of both the NbSi12- anion and neutral NbSi12 are D-6h symmetric hexagonal prisms with the Nb atom at the center. The perfect D-6h symmetric hexagonal prism of NbSi12- is electronically stable as it obeys the 18-electron rule and has a shell-closed electronic structure with a large HOMO-LUMO gap of 2.70 eV. The molecular orbital analysis of NbSi12- suggests that the delocalized Nb-Si-12 ligand interactions may contribute to the stability of the D-6h symmetric hexagonal prism. The AdNDP analysis shows that the delocalized 2c-2e Si-Si bonds and multicenter-2e NbSin bonds are important for the structural stability of the NbSi12- anion.