Nb2Se2I6: Eine neue Strukturvariante bei Niobchalkogenidhalogeniden mit Kettenstruktur

Nb2Se2I6: A New Structural Variation of Niobium Chalcogenide Halides with Chain Structure Single crystals of Nb2Se2I6, exhibiting a metallic lustre, (monoclinic, C2/c; a = 7.110(1), b = 13.899(3), c = 13.688(3) Å, β = 99.58(3)°; Z = 8) have been obtained by heating mixture of the elements (molar ratio Nb : Se : I = 3 : 1 : 7) in evacuated sealed fused silica tubes at 1073 K for two weeks. After rapid quenching, the tube was reheated to 773 K and then cooled at a rate of 2 K h–1. Crystals of the title compound formed at the colder part of the tube besides higher niobium iodides. Nb2Se2I6 can also be obtained by slow cooling of a stoichiometric mixture of the elements from 1073 K as a minor product besides triclinic NbSe2I2 [1]. The crystal structure is built up with one-dimensional infinite chains [Nb2Se2I4I4/2]. The main structural features are a short Nb–Nb distance (2.903(1) Å) and a short Se–Se distance (2.318(2) Å) which is expected for +4 and –1 oxidation states, respectively. Homeotypic phases with Nb2Y2X6 chains (Y = Se, Te; X = Br, I) are known [2] except for the combination Y = Se, X = I. They show a primitive rod packing of the Nb2Y2X6 chains in contrast to the title compound which shows a centered rod packing.