Structure and single crystal EPR study of Cu(II)(L-threonine)2.H2O

A. C. RIZZI; O. E. PIRO; E. E. CASTELLANO; O. R. NASCIMENTO; C.D. BRONDINO

INORGANICA CHIMICA ACTA

Elsevier

Año: 2000 vol. 305 p. 19 - 25

0020-1693

Abstract. We report the structure and single crystal EPR studies at 9.8 and 33.3 GHz of the title compound, [Cu(C4H8NO3)2]·H2O. The Cu(II) ion is in an elongated octahedral environment equatorially trans-coordinated by two oxygen atoms and two nitrogen atoms of threonine molecules which act as bidentate ligands (mean d(Cu-O)=1.95(1) and d(Cu-N)=1.98(1) A). It is axially coordinated by carboxylic oxygen atoms belonging to a pair of molecules translated in 9b (Cu-O distances of 2.478(8) and 2.972(3) A ). This axial O···Cu···O interaction gives rise to infinite copper ion chains along the b crystal axis. Neighboring chains are coupled through complex chemical paths including H-bonds and the amino acid side chain. Single crystal EPR spectra show a single, exchange-collapsed resonance at both microwave frequencies for any magnetic field orientation. We evaluated the crystal and the molecular g-tensors from the angular variation of the EPR line position. The results (g(perpendicular)=2.060(2) and g(parallel)=2.240(3)) indicate that the electronic ground orbital of the Cu ions is mainly of the 3dx2-y2 type. The analysis of the angular variation of the EPR linewidth allows us to estimate a mean exchange coupling constant |J:k |=1.45(5) K for the inter-chain chemical paths. .