W5As2.5P1.5: The First One-Dimensional Vertex-Linked W6Cluster

Abstract A new ternary phase W 5 As 2.5 P 1.5 has been synthesized and investigated by means of X-ray powder diffraction. The tetragonal unit cell dimensions are a =9.4729 (3) A and c =3.2414 (2) A (space group I 4/ m with Z =2). The crystal structure has been refined by the Rietveld method using the structure Mo 5 As 4 (Ti 5 Te 4 -type) as a related model ( R F =0.030 and R P =0.116 for 160 reflections and 30 refined parameters). In the structure, the metalloid sublattice (As, P) is wholly disordered and there is no interaction between the metalloid atoms, while W–W bonding leads to the formation of octahedral W 6 clusters inserted in X 8 cubes ( X =As, P). The significant aspect of this structure consists of the condensation of these W 6 X 8 units through two opposite tungsten atoms. This results in the formation of one-dimensional columns with the composition W 4 W 2/2 X 8/2 (W 5 X 4 ) parallel to the c -axis of the unit cell. Such a condensation of octahedral W 6 clusters has never been observed in solid state chemistry, the only examples of octahedral W 6 clusters being found in halide and chalcogenide chemistry but as isolated units. A general survey on Ti 5 Te 4 or derivative-type structure compounds is also given.