Synthesis and structures of tetranuclear 2-(dimethylamino)ethanethiolato complexes of zinc, cadmium and mercury involving both primary and secondary metal-halogen bonding

Two series of complexes of Zn, Cd and Hg with 2-(dimethylamino)ethanethiolate (L) ligands have been prepared. Complexes [M4L4X4] (series I) (X = Cl or Br) are obtained from anhydrous MX2, HL·HX and triethylamine in acetonitrile, and also from the metal acetate, HL·HX and sodium hydroxide in aqueous solution. Treatment of [Cd4L4X4] with NaL in acetonitrile-methanol gives [Cd4L6X2] (series II, Cd only). The structures of two complexes of series I, [Cd4L4Br4] 1 and [Hg4L4Cl4] 2, and of the series II complex [Cd4L6Cl2] 3, have been determined crystallographically, and are probably representative of the two series. All have a central centrosymmetric M4S4eight-membered ring in an extended-chair conformation with two opposite M atoms disposed one on each side of the M′2S4plane, and with aminothiolate ligands which are both S,N-chelating to M′ atoms and S-bridging between M and M′ atoms. The additional L ligands in 3 chelate the out-of-plane M atoms. The halogen atoms in 1 and 2 are terminally bonded to the M atoms, but two of them are also weakly bonded to both M′ atoms to give incipient triple bridging. In complex 3 the Cl atoms bridge the two M′ atoms and are only weakly bonded to one M atom each. These patterns of primary and secondary M-X bonding are compared with those in other structures having a similar central X2M2M′2S4core.