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要旨:
The crystal structure of tungsten (IT) bromide, W6Br12, was refined on
the basis of X-ray data of a twinned crystal (space group Bbcm (No. 64);
a = 11.799 Angstrom; b = 11.813 Angstrom; c = 14.790 Angstrom; Z = 4).
W6Br(12) forms the well-known Mo6Cl12 structure, with layers of
two-dimensional infinite networks
(2)(infinity)[(W6Br8i)(B2Br4/2a-a)-Br-a]. The cluster bond lengths and
bond angles show only small deviations from 4/mmm symmetry, which result
from internal strain in the 2D network. Mean distances are: (d) over
bar(W-W) = 2.633 Angstrom; (d) over bar(W-Br-i) = 2.630 Angstrom towards
the exo-Br-a; (d) over bar(W-Br-i) = 2.619 Angstrom towards the bridging
Bra-a; d(W-Br-a) = 2.550 Angstrom; d(W-Bra-a) = 2.656 Angstrom. The bond
angle at the bridging Bra-a atom is about 132 degrees. The structural
details of some isotypic compounds are compared and analyzed. It is
shown that size effects as well as electronic effects play an important
role in the tuning of the metal-to-metal bonds.
