V2Cu3Ga8, Mo2Cu3Ga8 and W2Cu3Ga8 - New compounds with a novel order variant of a bcc packing and motifs of self-similarity

摘要

Single crystals of the new compounds Tm2Cu3Ga8 (TM = V, Mo, W) were synthesised from the elements. Structure determinations of the isotypic compounds (cI104, space group 1 (4) over bar 3d, Z = 8; Mo2Cu3Ga8: a = 11.9171(10) angstrom, 613 refl., 23 param., R-1(F) = 0.022, wR(2)(F-2) = 0.047; W2Cu3Ga8: 11.9248(8) angstrom, 346 refl., 23 param., R-1(F) = 0.048, wR(2)(F-2) = 0.086; V2Cu3Ga8: 11.7861(14) angstrom, 374 refl., 24 param., R-1(F) = 0.033, wR(2)(F-2) = 0.081) showed a new cubic structure type which can be classified as an ordered defect variant of a bee packing with a' = 4a: [(TM)(2)(Cu)(3)(rectangle)(3)][Ga-8]. The coordination polyhedra of the transition metals consist of Ga-8-cubes with 3 sides capped by Cu leading to coordination number 11. The arrangement of the TMGa8Cu3-polyhedra is in a way they form itself a 3-fold capped cube. All compositions were confirmed by EDX measurements. (c) 2006 Elsevier Inc. All rights reserved.