Theoretical Investigations On The Structure And Energy Of Boiron-rich Sulfide Cluster B₆S

Boron and mixed-boron clusters have received considerable attention because of their wide applications and their essential roles in advancing chemical bonding models. Bearing the bright prospects as building blocks to form novel polymeric materials, the sulfur-rich boron sulfides have been greatly studied. However, the knowledge of the boron-rich boron sulfides is much rarer. In this paper, we report an extensive theoretical study on the structural, energetic and stability features of a hitherto unknown septa-atomic cluster B₆S at the CCSD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level. The local minimum isomers were obtained through our recently developed program"grid-based comprehensive isomeric search algrithm". We obtain the distinct B₆S structures as the starting geometries for the B3LYP/6-31G(d) optimization, which finally leads to 43 isomers with all real frequencies. Then the 43 isomers are all refined at the B3LYP/6-311+G(d) level followed by the CCSD(T)/6-311+G(2df) single-point calculations for some low-lying structures. The results show that the planar knife-like isomer B₅(-BS) 01 (0.0 kcal/mol) containing the -BS moiety is the lowest energy, followed by the quasi-planar belt-like isomer B₆(>S) 02 (6.7 kcal/mol) and the pyramid-like isomer B₆(>S) 03 (8.4 kcal/mol). To discuss the isomerism between various B₆S isomers, we investigate the interconversion transition states and perform a schematic potential energy survey of B₆S. In addition, we investigate the possible fragmentation channels, which can provide valuable information for understanding the stability of the clusters. Notably, the three singlet isomers all have good kinetic stability on the basis of the potential energy surface analysis. The B/S-centered wheel-like isomers are unfavorable in thermodynamics and kinetics. The triplet state structures generally can not compete with the singlet ones, so we don't discuss the triplet state in detail. The results are compared to the analogous and iso-valent cluster B₆O in both thermodynamics and kinetics. And NBO analysis was done to obtain more information. Our work is expected to provide useful information for understanding the structures and stability of boron sulfides.