The crystal structure of tungsten(II) bromide, W6Br12

The crystal structure of tungsten (II) bromide, W6Br12, was refined on the basis of X-ray data of a twinned crystal (space group Bbcm (No. 64); a = 11.799 Å; b = 11.813 Å; c = 14.790 Å; Z = 4). W6Br12 forms the well-known Mo6Cl12 structure, with layers of two-dimensional infinite networks ∞ 2[(W6WBr8 i)Br2 aBr4/2 a−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: [unk](W–W) = 2.633 Å [unk](W–Bri) = 2.630 Å towards the exo-Bra; [unk](W–Bri) = 2.619 Å towards the bridging Bra−a; d(W–Bra) = 2.550 Å; d(W–Bra−a) = 2.656 Å. The bond angle at the bridging Bra−a atom ias about 132°. 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.