Two isomorphous transition metal complexes displaying a coordinated tetrathionate unit: bis(4,4'-dimethyl-2,2'-bipyridine-κ(2)N,N')(tetrathionato-κ(2)S,S')cadmium(II) dimethylformamide disolvate and the zinc(II) analogue.

The isomorphous title compounds, [Tr(S4O6)(C12H12N2)2]·2C3H7NO (Tr = Cd(II) and Zn(II)), consist of metal centres to which one tetrathionate and two 4,4'-dimethyl-2,2'-bipyridine chelating ligands bind. The structures are completed by two symmetry-related dimethylformamide solvent molecules. Each metal-centred complex is bisected by a twofold axis running through the metal centre and halving the chelating tetrathionate dianion through the central S-S bond. The ancillary symmetry-related 4,4'-dimethyl-2,2'-bipyridine ligands act as chelates. This results in a distorted six-coordinate geometry, with similar Tr-O/N distances but central angles differing substantially from 90 and 180°. Both ligands are basically featureless from a geometric point of view, with torsion angles in both coordinated tetrathionate groups suggesting a trend linking metal size (covalent radius) and ligand `openness'. Packing is directed by (C-H)aromatic···O bridges and π-π offset stacked interactions defining chains along [001], further linked by weaker (C-H)methyl···O bridges, some of them mediated by the dimethylformamide solvent molecules.