Geometries, stabilities, and growth patterns of the bimetal Mo2-doped Sin (n=9-16) clusters:: A density functional investigation

The behaviors of the bimetal Mo-Mo doped cagelike silicon clusters Mo2Sin at the size of n = 9-16 have been investigated systematically with the density functional approach. The growth-pattern behaviors, relative stabilities, and charge-transfer of these clusters are presented and discussed. The optimized geometries reveal that the dominant growth patterns of the bimetal Mo-Mo doped on opened cagelike silicon clusters (n = 9-13) are based on pentagon prism MoSi10 and hexagonal prism MoSi12 clusters, while the Mo-2 encapsulated Si-n(n = 14-16) frames are dominant growth behaviors for the large-sized clusters. The doped Mo-2 dimer in the Si-n frames is dissociated under the interactions of the Mo-2 and Si-n frames which are examined in term of the calculated Mo-Mo distance. The calculated fragmentation energies manifest that the remarkable local maximums of stable clusters are Mo-2-doped Si-n with n = 10 and 12; the obtained relative stabilities exhibit that the Mo-2-doped Si-10 cluster is the most stable species in all different sized clusters. Natural population analysis shows that the charge-transfer phenomena appearing in the Mo-2-doped Si-n clusters are analogous to the single transition metal Re or W doped silicon clusters. In addition, the properties of frontier orbitals of Mo-2-doped Si-n (n = 10 and 12) clusters show that the Mo2Si10 and Mo2Si12 isomers have enhanced chemical stabilities because of their larger HOMO-LUMO gaps. Interestingly, the geometry of the most stable Mo2Si9 cluster has the framework which is analogous to that of Ni2Ge9 cluster confirmed by recent experimental observation (Goicoechea, J. M.; Sevov, S. C. J. Am Chem. Soc.2006, 128, 4155).