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Abstract:
Endohedral (interstitial) atoms are essential for almost all of the
rare-earth halide cluster complexes. Most of these contain octahedral
clusters, some are isolated, but the majority exhibits condensation by
common edges to structures of higher dimensionality. Higher coordination
numbers of the endohedral atoms are rare. Four examples of extended
cluster complexes with eight-coordinate endohedral atoms of sixth-period
elements (Re, Os, Ir) are presented. In the quasi-isostructural,
non-isotypic halides {ReGd(4)}Br(4) and (OsSc(4))Cl(4), square
antiprisms of gadolinium and scandium atoms, respectively, are connected
by two common faces to chains, surrounded and loosely connected by
halogenido ligands. The Re and Os atoms build a slightly bent chain with
only little bonding interactions. Chemical bonding is dominated by
endohedral atom-cluster atom and cluster atom-halide interactions. The
same is true for the two scandium bromides and {Os(3)Sc(12)}Br(16)Sc,
which contain chains of face-sharing square antiprisms and cubes in a
ratio of 2:1. Metal metal bonding is attested by short distances between
those endohedral Ir and Os atoms, respectively, which center the square
antiprisms (283 pm and 290 pm, respectively). Magnetic and conductivity
measurements on {Ir(3)Sc(12)}Br(16) reveal paramagnetism and a
small-band-gap semiconductor. This is in accord with electronic
structure calculations.
