title: Mn(approximately)2.4Mo6O9: first example of empty twin chains of edge-sharing M6 octahedra in transition metal cluster chemistry.
abstract: The novel ternary reduced molybdenum oxide Mn(approximately)(2.4)Mo(6)O(9) has been synthesized by solid-state reaction at 1400 degrees C for 96 h in sealed molybdenum crucibles. Electron diffraction studies showed that Mn(approximately)(2.4)Mo(6)O(9) presents a complex crystal structure with a 3d incommensurate modulation. The average crystal structure was determined on a single-crystal by X-ray diffraction in the orthorhombic space group Pnma with the following lattice parameters: a = 16.4824(2) A, b = 2.8273(2) A, c = 17.3283(2) A, Z = 4. The Mo network consists of empty twin chains of trans-edge-sharing octahedra that occur for the first time in a solid-state compound. The Mo-Mo distances within the chains range from 2.62 to 2.92 A, and the Mo-O distances from 1.99 to 2.17 A as usually observed in the reduced molybdenum oxides. Single-crystal resistivity measurements show that Mn(approximately)(2.4)Mo(6)O(9) is metallic between 4.2 and 300 K. The magnetic susceptibility data indicate paramagnetic behavior due to the Mn(2+) moment at high temperatures with a weak ferromagnetic behavior below 80 K.
authors.affiliation: Université de Rennes I, Institut de Chimie, Laboratoire de Chimie du Solide et Inorganique Moléculaire, U.M.R. nomicron. 6511, Avenue du Général Leclerc, 35042 Rennes Cedex, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Barrier
authors.forename: Patrick
authors.initials: P
authors.lastname: Gougeon
authors.forename: Richard
authors.initials: R
authors.lastname: Retoux
authors.forename: Henri
authors.initials: H
authors.lastname: Leligny