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Structure and single crystal EPR study of Cu(II)(l-threonine)2·H2O

2000; Elsevier BV; Volume: 305; Issue: 1 Linguagem: Inglês

10.1016/s0020-1693(00)00105-5

ISSN

1873-3255

Autores

Alberto C. Rizzi, Oscar E. Piro, E.E. Castellano, Otaciro R. Nascimento, Carlos D. Brondino,

Tópico(s)

Metal complexes synthesis and properties

Resumo

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) Å). It is axially coordinated by carboxylic oxygen atoms belonging to a pair of molecules translated in ±b (CuO distances of 2.478(8) and 2.972(3) Å). 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⊥=2.060(2) and g∣∣=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.

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