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Slow magnetic relaxation of a Mn(III) dimer in a Mn/Ca heteropolynuclear complex

AutorArauzo, Ana B.; Bartolomé, Elena ; Benniston, Andrew C.; Melnic, S.; Shova, S.; Luzón, Javier; Alonso, Pablo J.; Bartolomé, Juan
Fecha de publicación2016
CitaciónSCTE (2016)
ResumenNowadays, the laboratory synthesis of an artificial oxygen-evolving complex (OEC) has been the objective of many synthetic chemists. Particular attention has been given to mixed manganese-calcium compounds aimed to shed light on the tetranuclear arrangement of the manganese centers in the OEC. In this paper we present the magneto-structural characterization of the synthesised complex described by formula [Mn2Ca2(hmp)6(H2O)4(CH3CN)2](ClO4)3 (1). Cluster 1 crystallizes in the monoclinic space group C2/c with the cation lying on an inversion centre. The manganese and calcium ions of the [Mn2Ca2] core are six and seven coordinate, respectively. The distance Mn….Mn is 3.297 Å, and Mn….Ca is 3.490 Å. The complex was characterised by heat capacity and dc/ac magnetometry. Static thermo-magnetic results reflect a unique Mn(III) valence state, and high orthorombic crystal field parameters (D/kB=-6.2K, E/kB=-2.2K); at low temperature the system behaves as ferromagnetically coupled (JkB=1.1K) Mn dimers with a S=4 ground state. Ac magnetization in addition reveals the slow relaxation characteristics of a Single Molecule Magnet (SMM) below 4K. At zero magnetic field, an Orbach-type magnetic relaxation process is observed at high frequencies (T1 ~ 10-5 s), while a second low-frequency process (τs ~ 0.2 s) is induced by the application of an external d.c. magnetic field. The slow process is attribuited to a direct process with enhanced relaxation times due to phonon bottleneck effect.
DescripciónResumen del trabajo presentado a la 20th International Conference on Solid Compounds of Transition Elements, celebrada del 11 al 15 de abril de 2016 en Zaragoza (España).
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