Cobalt, nickel and copper complexes with N-alkylglycines: preparation, structural, spectroscopic and thermal characterization

The most simple standard amino acid glycine, H2NCH2COOH (GlyH), is one of the most common chelating ligands [1]. Structural data for several hundred metal complexes with this ligand can be found in the Cambridge Structural Database [2], while complexes with N-methylglycine (sarcosine, CH3NHCH2COOH ; SarH) appear to be quite rare. Metal complexes with higher N-alkylglycine derivatives were not known before this work. We have performed the reactions of copper(II), nickel(II) and cobalt(II) acetate with sarcosine and N-ethylglycine in aqueous solutions, and characterized the obtained complexes by X-ray crystallography, IR spectroscopy and thermoanalytical methods (TG/DTA and DSC). Both amino acid derivatives in their anionic form act as N, O-bidentate ligands, forming three types of complexes. Complexes of the type I are monomeric species of the formula trans-[M(Sar)2(H2O)2] (M = Cu, Ni) or trans-[M(Etgly)2(H2O)2] (M = Co, Ni). Copper(II) complex with N-ethylglycine (type II) is a coordination polymer of the formula [Cu(Etgly)2]n where the axial coordination sites are occupied by the carboxylate oxygen atoms from the neighbouring [Cu(Etgly)2] units. Cobalt(III) complex with sarcosine, [Co(Sar)2(μ-OH)]2 · 2H2O (type III), is a dimer containing the Co-Co bond. Details on the synthesis and structures of the complexes will be provided in the presentation.