Crystal structure and exchange pathways of the complex L-(trypthophyl-glycinato)copper(II)

The crystal structure and the EPR characterization of the compound Cu [C13H 13N3O3] is reported. It crystallizes in the P2(1)2(1)2(1) space group, with a = 8.2829(5), b = 9.347(2), c = 16.499(2) Angstrom and Z=4. The copper io n is in a distorted square planar coordination, bonded to two nitrogen and one oxygen atoms from one dipeptide and to an oxygen atom from a symmetry-r elated molecule. Thus, neighbor copper atoms at 5.14 Angstrom are connected by equatorial syn-anti carboxylate bridges giving rise to a chain structur e along the b-axis. The chains are connected via hydrogen bonds and cation- pi interactions, the latter being provided by the 'sandwich' structure invo lving each copper atom and two tryptophan residues from neighbor molecules. The EPR spectra of polycrystalline sample imply an essentially d(x2-y2) gr ound state orbital for the Cu(II) ions. The g-values reflect a slightly dis torted axial symmetry around the Cu(II) ions as expected from the structura l results. No hyperfine interaction is observed, which is indicative of the presence of exchange interactions between the copper atoms as suggested by the X-ray results as well. (C) 2001 Elsevier Science B.V. All rights reser ved.