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

Abstract

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 M₄S₄ eight-membered ring in an extended-chair conformation with two opposite M atoms disposed one on each side of the M′₂S₄ plane, 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′₂S₄ core.