SOME UNUSUAL TYPES OF AROMATICITY IN INORGANIC AND
ORGANOMETALLIC MOLECULES. R. B. King, Department of Chemistry,
University of Georgia, Athens, Georgia 30602
Three-dimensional aromaticity is now well-established in the deltahedral boranes
as an extension of the familiar two-dimensional aromaticity in benzene and related
aromatic hydrocarbons. Möbius aromaticity, in which the π-electron network is twisted as
in a Möbius strip, can be postulated to occur in the five-center four-electron bond in the
equatorial pentagon of pentagonal bipyramidal RhBi7(µ-Br)8. This delocalized bonding
in RhBi7(µ-Br)8 can be contrasted with the localized bonding in the ions
[RhBi6(µ-X)12]3– (X = Br, I). Another type of aromaticity is the -aromaticity found in
cyclopropanes. -Aromaticity can also account for the stability of triangular metal
carbonyls such as M3(CO)12 (M = Fe, Ru, Os) relative to square metal carbonyls such as
Os4(CO)16. Binodal aromaticity of a different type is found in polyoxometallates
including the cuboctahedral Keggin ions XM12O40n–(X = B, Si, Ge, P, etc) and the
vanadoborates [V6B20O50H8]8– with a hexagonal arrangement of the vanadium atoms.