Influence of the Metal–Metal Sigma Bonding on the Structures and Physical Properties of the Hexagonal Perovskite-Type Sulfides Sr9/8TiS3, Sr8/7TiS3, and Sr8/7[Ti6/7Fe1/7]S3

The structural and electronic consequences of the metal–metal sigma bonding in the hexagonal perovskite sulfides were examined by calculating the electronic band structures of Sr9/8TiS3 and Sr8/7TiS3, by synthesizing Sr8/7[Ti6/7Fe1/7]S3 and characterizing its crystal structure, and by measuring the magnetic susceptibilities of Sr9/8TiS3, Sr8/7TiS3, and Sr8/7[Ti6/7Fe1/7] S3. 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). Given the (TiS3)infinity chains aligned along the z direction, the only occupied d-block levels of each (TiS3) infinity chain are the most sigma bonding level of each (Oh)n oligomer, which is constructed from its nz2 orbitals. This "norbital two-electron" metal–metal sigma bonding controls the d-orbital density distribution and the Ti–Ti distances of the (Oh) n oligomers and is ultimately responsible for the semiconducting property of Sr9/8TiS3, Sr8/7TiS3, and Sr8/7[Ti6/7Fe1/7]S3. The Sr8/7[Ti6/7 Fe1/7]S3 structure is described by the trigonal symmetry, R3m (00?????)0s superspace group with the following parameters: as=11.4935(11) ?, cs=2.9986(7) ?, Q=0.57161(15) c*, and Vs=343.05(15) ?3