Influence of the metal-metal sigma bonding on the structures and physical properties of the hexagonal perovskite-type sulfides Sr9/8TiS3,Sr8/7TiS3, and Sr-8/7[Ti6/7Fe1/7]S-3

The structural and electronic consequences of the metal-metal sigma bonding in the hexagonal perovskite sulfides were examined by calculating the elec tronic band structures of Sr9/8TiS3 and Sr8/7TiS3, by synthesizing Sr-8/7[T i6/7Fe1/7]S-3 and characterizing its crystal structure, and by measuring th e magnetic susceptibilities of Sr9/8TiS3, Sr8/7TiS3 an Sr-8/7[Ti6/7Fe1/7]S- 3. The (TiS3)(infinity) chains of Sr9/8TiS3 and Sr8/7TiS3 contain oligomer units (Oh)(n) (n = 4, 5) made up of face-sharing TiS6 octahedra (Oh)(n) Giv en the (TiS3)(infinity) chains aligned along the z direction, the only occu pied d-block levels of each (TiS3)(infinity) chain are the most sigma bondi ng level of each (Oh), oligomer, which is constructed from its n z(2) orbit als. This "n-orbital two-electron" metal-metal sigma bonding controls the d -orbital density distribution and the Ti-Ti distances of the (Oh)(n) oligom ers and is ultimately responsible for the semiconducting property of Sr9/8T iS3, Sr8/7TiS3, and Sr-8/7[T6/7Fe1/7]S-3. The Sr-8/7[Ti-6/7 Fe-1/7]S-3 stru cture is described by the trigonal symmetry, Kim (00y)0s superspace group w ith the following parameters: a(s) = 11.4935(11) Angstrom, c(s) = 2.9986(7) Angstrom, q = 0.57161(15) c*, and V-s = 343.05(15) Angstrom (3). (C) 2001 Academic Press.