NIOBIUM CLUSTER COMPOUNDS WITH TRANSITION-METALS - K2MN[NB6CL18]

A new quaternary niobium cluster chloride, K2Mn[Nb6Cl18], has been syn thesized in a sealed quartz tube from stoichiometric amounts of NbCl5, niobium metal, KCl, and MnCl2 at 720 degrees C. The structure, as det ermined by single-crystal X-ray diffraction, is rhombohedral, space gr oup R (3) over bar (No, 148) with Z = 3 and has lattice parameters a = 914.01 (4) pm, c = 2522.9 (2) pm (hexagonal setting). The structure r efinement based on F-2 yielded wR2 = 0.040. (For comparison, a refinem ent based on F values yielded R1 = 0.016). The structure contains isol ated [Nb6Cl18](4-) clusters, separated by K+ and Mn2+ cations, being l ocated in an anticubeoctahedral and octahedral chloride coordination e nvironment, respectively. (C) 1996 Academic Press, Inc.