Insertion of a Single-Molecule Magnet inside a Ferromagnetic Lattice Based on a 3D Bimetallic Oxalate Network: Towards Molecular Analogues of Permanent Magnets

摘要

The insertion of the single-molecule magnet (SMM) [Mn~(III)(salen)(H_2O)]_2~(2+) (salen~(2-)=N,N'-ethylenebis-(salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [MnIII(salen)-(H_2O)]_2[Mn~(II)Cr~(III)(ox)_3]_2?(CH_3OH)?(CH_3CN)_2 (1). This cationic Mn_2 cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn~(III)(salen)(H_2O)]_2[Zn~(II)Cr~(III)(ox)_3]_2?(CH_3OH)?- (CH_3CN)_2 (2) and [In~(III)(sal_2-trien)][Mn~(II)Cr~(III)(ox)_3]?(H_2O)_(0.25)?- (CH_3OH)_(0.25)?(CH_3CN)_(0.25) (3), which are used as reference compounds. In 2 it has been shown that the magnetic isolation of the Mn_2 clusters provided by their insertion into a paramagnetic oxalate network of Cr~(III) affords a SMM behavior, albeit with blocking temperatures well below 500 mK even for frequencies as high as 160 kHz. In 3 the onset of ferromagnetism in the bimetallic Mn~(II)Cr~(III) network is observed at T_c=5 K. Finally, in the hybrid compound 1 the interaction between the two magnetic networks leads to the antiparallel arrangement of their respective magnetizations, that is, to a ferrimagnetic phase. This coupling induces also important changes on the magnetic properties of 1 with respect to those of the reference compounds 2 and 3. In particular, compound 1 shows a large magnetization hysteresis below 1 K, which is in sharp contrast with the near-reversible magnetizations that the SMMs and the oxalate ferromagnetic lattice show under the same conditions.