Crystal Structure and Magnetic Interactions in Bis(D,L-alaninato)copper(II) Monohydrate

R. CALVO; P. R. LEVSTEIN; E. E. CASTELLANO; S. M. FABIANE; O. E. PIRO; S. B. OSEROFF

INORGANIC CHEMISTRY

American Chemical Society

Año: 1991 vol. 30 p. 216 - 220

0020-1669

The title compound, Cu(H2CHCH3CO2)2.H2O [Cu(D ,L-ala)2.H2O] crystallizes in the space group C2/c, with a = 12.087 (3) A, b = 9.583 (3) A, c = 8.973 (3) A, beta =110.85 (2)º, and Z = 4. The structure was solved from 737 X-ray reflections and refined to R= 0.032. The Cu(11) ion is at an inversion center, bound to the amino nitrogen and to one of the carboxylate oxygens of two symmetry-related (D and L) alanine molecules. Two water oxygens complete an elongated octahedral arrangement of ligands around the copper ions. The water oxygens are at the common apical positions of neighboring coordination octahedra and are strongly hydrogen-bonded to carboxylate oxy ens of two other neighboring molecules. The corner sharing octahedra are arranged in chains parallel to the c-axis at a distance of 4.487 A with an interchain distance of 7.712 A.  Magnetic susceptibility data in powdered Cu(D,L-ala)z.HzO between 1.83 and 44 K show, above 10 K, a Curie-Weiss behavior with theta = -2.10 K. The deviation from the Curie-Weiss law observed below theta, can be interpreted in terms of a one-dimensional spin chain model, with antiferromagnetic exchange-coupling constant J / k = -1.61 K between nearest-neighbor Cu(I1) ions. Room-temperature single-crystal EPR data show one exchange-collapsed resonance for all magnetic field orientations and are used to obtain the g-tensors of individual Cu(D,L-ala)2.H20 molecules. The magnetic coupling between coppers is discussed in terms of the possible paths for superexchange interaction allowed by the lattice, and the results are compared with those obtained from similar studies in other copper amino acid complexes.