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A novel pattern of condensed tricapped trigonal prismatic clusters for M2Ta11Se8(M ≡ Fe, Co, Ni)

Journal of the Less Common Metals
Publication Date
DOI: 10.1016/0022-5088(88)90211-1


Abstract The tantalum-rich selenides M 2Ta 11Se 8 (M ≡ Fe, Co, Ni) have been prepared and characterized by means of X-ray diffraction experiments. They crystallize in the orthorhombic space group Pnnm with two formula units in the cell: a = 1204.5(1) pm, b = 1964.1(2) pm and c = 337.75(3) pm for Fe 2Ta 11Se 8; a = 1203.0(1) pm, b = 1961.6(2) pm and c = 336.77(4) pm for Co 2Ta 11Se 8; a = 1196.4(1) pm, b = 1953.2(2) pm and c = 339.94(3) pm for Ni 2Ta 11Se 8. The structures exhibit M-centred tricapped trigonal prismatic tantalum clusters condensed via trans-triangulated trigonal prism faces along the c direction and via one out of three capping tantalum atoms. Thus, the clusters are arranged in twin columns, which are surrounded by low coordinated selenium atoms (coordination numbers: 3, 4, 5, 6). The selenium atoms also provide the three-dimensional linkage of the metal framework. Evidence exists for weak pairwise 3d metal interactions in Fe 2Ta 11Se 8 and Co 2Ta 11Se 8 that are associated with a break of symmetry.

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