Effect of hydrogen bonding on the coordination - Part 2. Semi-coordination in trans-di(salicylato)bis(1,3-diaminopropane-N,N ')copper(II)

摘要

The crystal and molecular structure of trans-di(ortho-hydroxobenzoato-O)bis(1,3-diaminopropane-N,N')copper(II) [ortho-hydroxobenzoate = salicylate hereafter] determined by single crystal X-ray diffraction methods at T = 193(2) K. The structure is composed of monomeric complex units with the central copper(II) ion occupying a centre of symmetry. The coordination polyhedron can be described as axially elongated distorted octahedron with the axial Cu-O bond length of 2.559(3) Angstrom indicating semi-coordination. There is notable asymmetry in the coordinated 1,3-diaminopropane molecule, which forms a six-membered chelate ring displaying Cu-N1-C1 and Cu-N2-C3 angles of 121.5(2) and 117.4(2)degrees, respectively. This deviation may be correlated to differences in hydrogen bonding between the amino groups and the non-coordinated oxygen atoms of the salicylate anions. The coordinated salicylate anion shows considerable declination of 28.9 degrees, which may be correlated to intramolecular hydrogen bonding. The electronic properties of benzoate anions were studied by Natural Bond Order (NBO) analyses for optimised model compounds at the MP2/6-311 + G*//MP2/6-311 + G* level of theory. The results suggest that semi-coordination is mainly characterised by concomitant electrostatic attraction of the charges at the central copper(II) cation and repulsion between an electron lone pair of a ligand atom and the electron lone pair at the copper(II) 3d(z2) atomic orbital. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 31]