Structural and spectral studies of N-alkyloxamates and their complexes: X-ray structures of MeHNCOCOOK and [Cu(EtHNCOCOO)(2)], and vibrational studies

This work is devoted to structural and vibrational studies of N-alkyloxamat es and their complexes. The structures of MeHNCOCOOK and [Cu(EtHNCOCOO)(2)] have been determined by single-crystal X-ray crystallography. The potassiu m salt crystallizes in the monoclinic space group P2(1)/n and the copper(II ) complex in the triclinic space group P (1) over bar. The lattice constant s are a = 3.882(2), b = 10.175(1), c = 13.004(1), beta = 97.04(1)degrees fo r MeHNCOCOOK and a = 5.013(1), b = 6.996(1), c = 8.575(1) Angstrom, alpha = 73,54(1), beta = 85.66(1), gamma = 71.22(1)degrees for [Cu(EtHNCOCOO)(2)]. The salt has a trans secondary amide group and the K- ion is surrounded by seven O atoms belonging to six different N-methyloxamate(-1) moieties. The ligand EtHNCOCOO- behaves as a bidentate chelate in the trans square plana r copper(II) complex with ligated atoms being the amide and one of the carb oxylate oxygens. The copper(II) complex was characterized by its room-tempe rature magnetic susceptibility and solid-state d-d spectrum. A detailed com parison of the vibrational spectra (FT-IR, FT-Raman) of [Cu(EtHNCOCOO)(2)] with the corresponding potassium salt, EtHNCOCOOK, is presented. The vibrat ional data are discussed in terms of the nature of bonding and the known st ructure of the copper(II) complex. Quantum-chemical calculations were perfo rmed to obtain the equilibrium geometries and torsional energies for an iso lated oxamate(-1) ion (H2NCOCOO-) and its hypothetical square planar zinc(I I) complex. (C) 2001 Elsevier Science B.V, All rights reserved.