Dihydroxyacetone (DHA) monomer complexes with CaBr2 and CdCl2.

Two hydrated complexes of monomeric dihydroxyacetone (DHA; the simplest ketose), viz. the calcium bromide complex bis(mu-dihydroxyacetone)bis[tetraaquacalcium(II)] tetrabromide (isomorphous with the chloride compound reported previously), [Ca(2)(C(3)H(6)O(3))(2)(H(2)O)(8)]Br(4), (2e), and the cadmium chloride complex poly[[bis(mu-dihydroxyacetone)bis[bis(dihydroxyacetone)cadmium(II)]] [diaquatetradeca-mu-chlorido-dichloridohexacadmium(II)] tetrahydrate], {[Cd(2)(C(3)H(6)O(3))(6)][Cd(6)Cl(16)(H(2)O)(2)] x 4 H(2)O}(n), (2f), are described. The Ca(2+) or Cd(2+) ions are bridged by the carbonyl O atoms from two DHA molecules to form centrosymmetric dimers, with Ca...Ca distances of 4.334 (2) and 4.300 (2) A in (2e), and a Cd...Cd distance of 4.195 (1) A in (2f). Almost identical in shape, the eight-coordinate polyhedra of the Ca(2+) and Cd(2+) ions are composed of 2n O atoms from n DHA molecules [n = 2 in (2e) and n = 4 in (2f)] and are completed by four water molecules in (2e). DHA molecules chelate the cations via both the hydroxyl and carbonyl groups and exist in an extended conformation, with both hydroxyl groups being synperiplanar to the carbonyl O atom. The crystal structures are stabilized by similar extensive O-H...X (X = Cl or Br) and O-H...O hydrogen-bond networks involving all hydroxyl groups and the water molecules.