Synthesis of Zinc and Cadmium O-Alkyl Thiocarbonate and Dithiocarbonate Complexes and a Cationic Zinc Hydrosulfide Complex

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Treatment of Zn(II) and Cd(II) hydroxide complexes of the tris(2-pyridylmethyl)amine (TPA) ligand with COS or CS2 in protic solvents (MeOH or EtOH) resulted in [(TPA)Zn–SC(S)OCH3]ClO4 (1), [(TPA)Zn–SC(O)OCH3]BF4 (2), [(TPA)Zn–SC(O)OCH3]ClO4 (3), [(TPA)Zn–SC(O)OCH2CH3]BF4 (4), [(TPA)Cd–SC(S)OCH3]ClO4 (5) and [(TPA)Cd–SC(O)OCH3]ClO4 (6). The molecular structures of 1, 2, 5 and 6 were determined by X-ray crystallography. Complexes 2, 3 and 4, unlike 1, 5 and 6, are easily hydrolyzed upon treatment with water in CH3CN to give zinc hydrosulfide complexes of the form [(TPA)Zn–SH]X (X = BF4 (7) and ClO4 (8)), as evidenced by spectroscopic methods and the crystal structure of 7. These complexes may be prepared more directly by (a) reacting equimolar amounts of TPA, Zn(ClO4)2·6H2O and Me4NOH·5H2O with COS in CH3CN or (b) treating [((TPA)Zn)2(μ-OH)2](ClO4)2 with H2S. Moreover, reactivity and density functional theory computational studies comparing the cationic hydrosulfide complexes 7 and 8 with the neutral zinc hydrosulfide complexes supported by tris(pyrazolyl)borate ligands have been conducted and subtle differences between the two types of hydrosulfide complexes have been determined.