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Abstract:
Black platelets of Bi39.67(7)Ru2Br35.0(2) were crystallized from a melt
of Bi, BiBr3, and Ru. In the tetragonal crystal structure [P4/mbm, a =
1311.92(6) pm, c = 3018.2(4) pm at 155(5) K], cluster cations
[(Bi-8(2+))Ru2+(Bi-8(2+))] are embedded in a matrix of disordered
bromido-bismuthate(III) groups. A thorough analysis of the disorder in
the anionic part enabled the unambiguous assignment of the cluster
charge. The eta(4)-coordination of the two Bi-8(2+) square antiprisms to
the Ru-II atom in the sandwich complex resembles the bonding of Bi-5(+)
and Bi-8(2+) in the clusters [(Bi-5(+))Ru+(Bi4Br4)Ru+(Bi-5(+))] and
[(Bi-8(2+))Ru+(Bi4Br4)Ru+(Bi-5(+))] as well as of Bi-4(2-) in
(1)(infinity)[(Bi-4(2-))Ru+(Bi4Br4)Ru+]. By combining crystal chemical
considerations for all mentioned compounds and using quantum chemical
calculations, a common bonding scheme for the coordination compounds of
bismuth polycations and polyanions was established. The
eta(4)-coordinating bismuth polycations and polyanions act as six
electron donors, comparable to nido-carborane ligands, Zintl anions
E-9(4-) and E-5(6-) (E = Si to Pb), cyclopentadienyl ligands, or the
cyclobutadiene dianion. The electron count for the transition metal is
18 in all finite clusters.
