Repositori URV

Identificador: PC:3126

Handle: https://hdl.handle.net/20.500.11797/PC3126

Autors:
De Graaf, C.Maxim, C.Saureu, S.Ferlay, S.Wais, M.Robert, V.Train, C.

Resum:
Three X2+ bisamidinium dications are used as template for the formation of oxalate-based bimetallic [MnCr] compounds 1-3 of formula X[MnII(CH3OH)CrIII(ox)3]2·nS (X2+ = C14N4H20 2+ (cation A, compound 1), C14O2N4H202+ (cation B, compound 2), C16N4H24 2+ (cation C, compound 3); n=4 (1-2), 2 (3); S= CH3OH (1-2), CH3CN (3)). The single-crystal X-rays analysis reveals that in 1-3, a Mn-Cr oxalate-bridged bimetallic coordination network is formed, displaying corrugated two-dimensional (2D) layers based on heptacoordinated manganese(II) ions, with six oxygen atoms from three bis(bidentate) oxalate ions and one oxygen atom from a coordinated methanol molecule in the coordination sphere. In all cases, the coordination environment of manganese(II) is close to a Capped Trigonal PRism (CTPR). This evolution is related to the disymmetrization of one of the three oxalate linkages. Measurements of the magnetic properties revealed a continuous increase of the χ MT product, where χ M is the magnetic susceptibility, when the temperature is lowered from 300K to 5K, indicating the presence of a dominant ferromagnetic interaction in 1-3. The Curie-Weiss temperatures deduced from the fit of the magnetic susceptibility in the paramagnetic phase are 5.87K, 4.40K and 3.98K for 1, 2 and 3 respectively. From a mean field approach, an average weak ferromagnetic exchange interaction of 0.62K, 0.42K and 0.54K respectively can be deduced. Ab initio calculations up to the DDCI-2 level were performed on [MnCr] dimeric units. They allow to evaluate the exchange interaction for each type of bridges present in the three compounds. An effect of the asymmetry of the bridge on the exchange interaction is observed but not in a systematic way.