Novel species for the sulfur zoo: isomers of S8

Ab initio calculations at the G3X(MP2) level have been employed to examine the structures and energies of S8 and H2S6 isomers. A cluster structure with a spiraling chain of 8 atoms (C2 symmetry) lies close in energy (33 kJ mol−1) to the eight-membered crown-S8 global energy minimum. This cluster species is characterized by two three-coordinate atoms and a rectangular arrangement of four sulfur atoms at the formal chain-ends. This unusual cluster geometry can be rationalized in terms of a weak π*–π* bond between the two π* orbitals of the chain-end groups. A low-energy cluster-type structure is also predicted for hexasulfane.