Zinc, cadmium and mercury dithiocarboxylates: synthesis, characterization, structure and their transformation to metal sulfide nanoparticles

Abstract

Reactions of M(OAc)₂·nH₂O and M(OAc)₂(tmeda) with dithiocarboxylic acids gave [M(S₂CTol)₂]_n (1) (M = Zn or Cd; Tol = C₆H₄Me-4) and [M(S₂CAr)₂(tmeda)] (3) (M = Zn, Cd, Hg; Ar = Ph or Tol), respectively, in high yields as deep-colored crystalline solids. The former are soluble in pyridine to give pyridine adducts [M(S₂CTol)₂(py)] (2). These complexes were characterized by elemental analysis, UV/Vis and NMR (¹H, ¹³C) spectroscopy. The absorptions in the electronic spectra have been assigned to ligand-to-ligand charge-transfer transitions. The crystal and molecular structures of the monomeric species [Zn(S₂CTol)₂(py)] (2), [Zn(S₂CPh)₂(tmeda)] (3a), [Zn(S₂CTol)₂(tmeda)] (3b) and [Cd(S₂CTol)₂(tmeda)] (3d) have been established by X-ray crystallography. In [Zn(S₂CTol)₂(py)], chelating dithiocarboxylate ligands and pyridine define a coordination geometry intermediate between square pyramidal and trigonal bipyramidal. In each of 3a and 3b, tetrahedral N₂S₂ coordination geometries are found as the dithiocarboxylate ligands are effectively monodentate; evidence for the greater coordination potential is found for ^-S₂CTol over ^-S₂CPh. Chelating dithiocarboxylate ligands in [Cd(S₂CTol)₂(tmeda)] (3d) lead to an octahedral geometry. Thermal behavior has been studied by thermogravimetric analysis. The [M(S₂CAr₎₂(tmeda)] complexes underwent a three-step decomposition. Pyrolysis in the temperature range 300-500°C and solvothermal decomposition in ethylenediamine and hexadecylamine (HDA) gave metal sulfide nanoparticles. The MS (M = Zn, Cd, Hg) nanoparticles were characterized by XRD, EDAX, absorption/emission spectroscopy and electron microscopy (TEM). Solvothermal decomposition gave hexagonal phases of nanoparticles whereas heating in a furnace gave cubic ZnS and HgS, and hexagonal CdS.