Planar Tetracoordinate Boron and Pentacoordinate Boron in B6S5 Clusters

At the level of B3LYP/def2-TZVP optimization and CCSD single point energy, B6S5n (n=0, +1, +2) was utilized to validate the valuable effect of peripheral sulfur atom on constructing planar coordinated boron. The structures of global energy minimum(GEM) and the second lowest energy minimum in three charge states are purely planar ones, and their structures are very similar. Only their order is exchanged with the loss of the electrons. There exists a planar pentacoordinate boron in the GEM structure of D-5h-B6S5 due to the 18 electron rule, and there are all the planar tetracoordinate borons in the GEM structure of B6S5n (n=0, +1, +2). Meanwhile, the sulfur-bridging bonding is another key factor to maintain their planar molecular structures.