Ta 11 Si 2 Se 8 – Condensed Tetrakaidecahedral Ta 9 Si Clusters Arranged to an Open Network Structure

Ta 11 Si 2 Se 8 was synthesized from a pre‐reacted mixture of the elements in a sealed tantalum tube at 1570 K. Mo‐doped crystals were obtained in a welded molybdenum crucible by a chemical transport reaction using TeI 4 as a transport agent. The structure of Mo 0.11 Ta 10.89(2) Si 2 Se 8 has been determined by single crystal X‐ray means [ Pnnm , Z = 2, a = 1184.4(1) pm, b = 1939.4(1) pm, c = 346.48(2) pm, wR 2 = 0.069]. The structure of the ternary phase was verified by means of a Rietveld profile fit of a powder X‐ray diffractogram. The silicide is isotypic with Ta 11 Ni 2 Se 8 . The structure is composed of Si‐centred, tricapped trigonal prismatic Ta 9 Si clusters. The tetrakaidecahedral Ta 9 Si clusters are fused into twin chains by sharing the Ta pr atoms of facing triangulated prism faces and one out of three capping atoms Ta c . Intercluster linkage of the remaining Ta c atoms generates a microporous ∞ 3 [SiTa 2 c Ta 1 /2 c Ta 6/2 pr ] substructure. The channels of the metal network are sheathed by three‐, four‐, five‐, and sixfold coordinated Se atoms. Four‐probe dc resistivity measurements revealed the Mo‐doped phase to be a moderate metallic conductor. The bonding interactions contributing to the stability of Ta 11 Si 2 Se 8 and distinctions in bonding for Ta 11 Si 2 Se 8 and Ta 11 Ni 2 Se 8 are analysed on the basis of semi‐empirical extended Hückel calculations.