Crystal and electronic structures of one-dimensional transition metal thiophosphates:: ANb2PS10 (A=Na, Ag)

A new quaternary compound NaNb2PS10 was prepared by reacting the mixture of Nb, P2S5, S and Na2S at 750degreesC. AgNb2PS10 was also synthesized by the direct solid-state reaction of Ag, Nb, P and S at 900degreesC. Their structures were determined by single-crystal X-ray diffraction method. The needle-shape crystals of the two compounds crystallize in the common monoclinic space group C2/c. NaNb2PS10 crystallizes into purple crystals with cell dimensions of a = 24.7634(10) Angstrom, b = 7.8407(11) Angstrom, c = 12.947(3) Angstrom, beta = 90.83(2)degrees and Z = 8. AgNb2PS10 ad dark-gray crystals with cell dimensions of a 23.9609(10) Angstrom, b = 7.7692(11) Angstrom, c = 12.910(3) Angstrom, beta = 94.49(2)degrees and Z = 8. These structures consist of one-dimensional infinite chains built by [Nb2S12] and [PS4] units. The Nb atoms are centered in distorted bicapped trigonal prismatic polyhedra and the neighboring polyhedra share square faces and edges to make Nb-Nb pairs. [PS4] units are tetrahedra composed of one S atom at the prism corner and two other capping S atoms and an additional S atom. Ag+ and Na+ cations in NaNb2PS10 and AgNb2PS10 reside in the van der Waals gap of sulfur atoms between infinite chains. Calculation of the electronic structure shows that the two compounds are semiconducting materials. Optically measured band gaps were 1.72 and 1.77eV for NaNb2PS10 and AgNb2PS10, respectively. (C) 2002 Elsevier Science (USA).