Syntheses and crystal structures of the first bromofluorides in niobium cluster chemistry: Nb6Br8F7 and Na2NbF6-(Nb6Br4F11)

We have synthesized by solid state chemistry and structurally characterized by single-crystal X-ray diffraction two new cluster compounds based on Nb6 L12L6a units (L = Br and/or F), namely, Nb6Br8F7 and Na2NbF6-(Nb6Br4F11). N b6Br8F7 crystallizes in the trigonal system (space group, R3c; Z = 6; a = 9 .6373 (6) Angstrom; c = 35.415 (2) Angstrom; R = 0.0359) while Na2NbF6-(Nb6 Br4F11) (space group, Pm3m; Z = 1; a = 8.1765 (6) Angstrom; R = 0.0325) cry stallizes in the cubic system, In both structures, fluorine and bromine are randomly distributed on the inner ligand positions (L-1) that edge bridge the octahedral Nb, cluster, In Nb,Sr,F,, bromine fully occupies the apical ligand positions (L-a) whereas these positions are fully occupied by fluori ne in Na2NbF-(Nb6Br4F11). The structural correlation between both compounds is discussed as well as the specificity of fluorine in the niobium cluster chemistry, (C) 2001 Academic Press.