Oxalato-bridged [CIICrIII]and [MIICrIII] binuclear complexes:: Synthesis, crystal structures, magnetic and EPR investigations

Two new heterobinuclear complexes, [(bipy)(C2O4)Cr(mu-C2O4)Cu(Hfsaaep)(H2O)](.)2H(2)O (1) and [(phen)(C2O4)Cr(mu-C2O4)Mn(phen)(2)(N-3)](H2O)-H-. (2) have been obtained by using bis(oxalato)chromium(III) anions, [Cr(AA)(C2O4)(2)](-), as building blocks [AA = 2,2'-bipyridine (bipy); 1,10-phenanthroline (phen)]. The crystal structures of the two complexes have been solved. These complexes comprise neutral oxalato-bridged Cr-III-Cu-II and Cr-III-Mn-II units. The [Cr(AA)(C2O4)(2)](-) anion acts as a bidentate ligand toward Cu-II in compound 1 and as a monodentate ligand toward Mn-II in compound 2. The copper(II) ion in 1 exhibits a slightly distorted square bipyramidal stereochemistry, with the aqua ligand and one of the bridging oxalato oxygen atoms disposed in the apical positions [Cu(1)-O(1w) = 2.360(3) Angstrom and Cu(1)-O(4) = 2.504(2) Angstrom]. The second bridging oxalato oxygen atom [Cu(1)-O(2) = 2.0747 (18) Angstrom] and the N,N,O-type Hfsaaep ligand are located in the basal plane. The distance between the Cr-III and Cu-II ions across the bridging oxalate unit is 5.506 Angstrom. The Mn-II ion in compound 2 is hexacoordinate (two chelating phen ligands, one oxalato bridging oxygen, and one terminal azido group). The intermolecular (CrMnII)-Mn-III... distance is 5.257 Angstrom. The magnetic properties of the two complexes have been investigated. The magnetic coupling between Cr-III and Cu-II in 1 was found to be ferromagnetic (J = +1.4 cm(-1)). The nature of the ground state (S = 2) has been further confirmed by plotting the magnetization-versus-field curve. An antiferromagnetic interaction was found between Cr-III and Mn-II in compound 2 (J = -1.9 cm(-1)). The magnetization-versus-field curve indicates the occurrence of a crossover between the Zeeman components: M-S = -1 (ground state S = 1), M-S = -2, from the first excited state (S = 2), and M-S = -3, from the second excited state. The EPR spectra of the two compounds are discussed. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.