Metal-metal bonding and mixed-valent tantalum in La2Ta3S2O8

摘要: Abstract The compounds La2Ta3S2O8 and La2Nb3S2O8 have been prepared characterized. From singlecrystal X-ray diffraction measurements, crystallizes in space group D122h-Pnnm of the orthorhombic system with four formula units a cell dimensions = 9.876(7), b 11.768(7), c 7.658(5)A (T 111 K). compound is isostructural to series oxyselenides Ln2Ta3Se2O8 (Ln La, Ce, Pr, Nd) previously reported. three-dimensional structure built up from layers tricapped trigonal-prismatically coordinated La atoms alternating octahedrally Ta atoms. One atom distorted octahedral site surrounded by six O forms edge-sharing dimers itself. other environment two S its coordination sphere chains bridging one-electron band was calculated tight-binding method an extended Huckel-type Hamiltonian. calculations support hypothesis separate Ta(+4) Ta(+5) sites Ln2Ta3Q2O8 (Q Se) point driving force behind TaTa pairing that occurs along chains. has same structure, as deduced comparison powder patterns.