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A Family of Oxamido-Bridged MnIICuII Bimetallic Molecular-Based Ferrimagnets:  Synthesis, EXAFS Structural Characterization, and Magnetic Properties

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posted on 16.01.1997, 00:00 authored by Rafael Ruiz, Céline Surville-Barland, Yves Journaux, Jean Christophe Colin, Isabel Castro, Beatriz Cervera, Miguel Julve, Francesc LLoret, Fernando Sapiña
A family of related compounds of general formula (PPh4)2Mn2[Cu(L)]3·nH2O have been synthesized, where PPh4+ is the tetraphenylphosphonium cation and L stands for o-phenylenebis(N‘-benzyloxamidate) (PhMe2opbox) (1), o-phenylenebis[N‘-(3-phenylpropyl)oxamidate] (PhPr2opbox) (2), and o-phenylenebis[N‘-(4-phenylbutyl)oxamidate] (PhBu2opbox) (3). The analysis of the XANES and EXAFS spectra of 3 at both Mn and Cu K-edges reveals the occurrence of an oxamidato-bridged MnIICuII two- or three-dimensional structure with Mn···Cu separation of 5.4 Å. Each manganese atom is surrounded by three Cu(L) bisbidentate entities which define an octahedral MnO6 environment, while each copper atom is in an essentially square-planar CuN4 surrounding. The magnetic properties of the three compounds have been investigated in the 1.8−300 K temperature range. Compounds 13 show characteristic ferrimagnetic behavior with a minimum in the χT versus T plot, and abrupt ferromagnetic phase transition below a critical temperature Tc equal to 12.5, 11.5, and 13.5 K for 13, respectively. The magnetization versus magnetic field curve for 3 indicates that in the magnetically ordered phase, all the manganese local spins are aligned along one direction and the copper local spins along the opposite one, confirming thus the antiferromagnetic nature of the interaction between manganese(II) and copper(II) ions through the oxamidato bridge.