Oxalato‐Bridged [CuIICrIII] and [MnIICrIII] Binuclear Complexes: Synthesis, Crystal Structures, Magnetic and EPR Investigations

Abstract

AbstractTwo new heterobinuclear complexes, [(bipy)(C2O4)Cr(μ‐C2O4)Cu(Hfsaaep)(H2O)]·2H2O (1) and [(phen)(C2O4)Cr(μ‐C2O4)Mn(phen)2(N3)]·H2O (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 CrIII−CuII and CrIII−MnII units. The [Cr(AA)(C2O4)2]− anion acts as a bidentate ligand toward CuII in compound 1 and as a monodentate ligand toward MnII 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) Å and Cu(1)−O(4) = 2.504(2) Å]. The second bridging oxalato oxygen atom [Cu(1)−O(2) = 2.0747(18) Å] and the N,N,O‐type Hfsaaep ligand are located in the basal plane. The distance between the CrIII and CuII ions across the bridging oxalate unit is 5.506 Å. The MnII ion in compound 2 is hexacoordinate (two chelating phen ligands, one oxalato bridging oxygen, and one terminal azido group). The intermolecular CrIII···MnII distance is 5.257 Å. The magnetic properties of the two complexes have been investigated. The magnetic coupling between CrIII and CuII 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 CrIII and MnII in compound 2 (J = −1.9 cm−1). The magnetization‐versus‐field curve indicates the occurrence of a crossover between the Zeeman components: MS = −1 (ground state S = 1), MS = −2, from the first excited state (S = 2), and MS = −3, from the second excited state. The EPR spectra of the two compounds are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)