Preparation, structural characterization and vibrational spectroscopic studies of transition metal complexes of singly- and doubly-deprotonated N-methyl-2-thiooxamic acid

Abstract

Synthetic procedures are described that allow access to the new monomeric complexes [M(HA)2(H2O)2]·2H2O (M = Mn or Co), [M(HA)2(H2O)2] (M = Fe, Ni or Zn) and [Cu(HA)2], and to the polymeric compounds [MA(H2O)] n (M = Mn, Co, Ni or Zn) and [CuA] n , where H2A = N-methyl-2-thiooxamic acid. The X-ray crystal structure of [Mn(HA)2(H2O)2]·2H2O reveals a trans, cis, cis octahedral geometry around the metal ion. The singlydeprotonated ligand behaves as a bidentate chelate with ligated atoms being the neutral thioamide sulfur and one of the carboxylate oxygens. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, magnetic susceptibilities and spectroscopic (e.s.r., ligand field, i.r., far-i.r., Raman) studies. The vibrational analysis of the complexes is presented using OH/OD, NH/ND, CH3/CD3 and metal isotopic substitutions. All data are discussed in terms of the nature of bonding in conjunction with known or assigned structures. The dianion A2− acts as a bis-bidentate O,N/O,S bridging ligand yielding highly symmetrical squares planar (CuII) and octahedral (MnII, CoII, NiII and ZnII) polymeric compounds.