Single-Molecule Magnet Behavior in Heterometallic MII−MnIII2−MII Tetramers (MII = Cu, Ni) Containing MnIII Salen-Type Dinuclear Core
Résumé
The linear-type heterometallic tetramers, [MnIII2(5-MeOsaltmen)2MII2(L)2](CF3SO3)2*2H2O (MII = Cu, 1a; Ni, 2a), where 5-MeOsaltmen2- = N,N'-(1,1,2,2-tetramethylethylene) bis(5-methoxysalicylideneiminate), and H2L = 3-{2-[(2-hydroxy-benzylidene)-amino]-2-methyl-propylimino}-butan-2-one oxime, have been synthesized and characterized from structural and magnetic points of view. These two compounds are isostructural and crystallize in the same monoclinic P21/n space group. The structure has a [MII−NO−MnIII−(O)2−MnIII−ON−MII] skeleton, where −NO− is a linking oximato group derived from the non-symmetrical Schiff-base complex [MII(L)] and −(O)2− is a biphenolato bridge in the out-of-plane [Mn2(5-MeOsaltmen)2]2+ dimer. The solvent-free compounds, 1b and 2b, have also been prepared by drying of the parent compounds, 1a and 2a, respectively, at 100 °C under dried nitrogen. After this treatment, the crystallinity is preserved, and 1b and 2b crystallize in a monoclinic P21/c space group without significant changes in their structures in comparison to 1a and 2a. Magnetic measurements on 1a and 1b revealed antiferromagnetic MnIII***CuII interactions via the oximato group and weak ferromagnetic MnIII***MnIII interactions via the biphenolato bridge leading to an ST = 3 ground state. On the other hand, the diamagnetic nature of the square planar NiII center generates an ST = 4 ground state for 2a and 2b. At low temperature, these solvated (a) and desolvated (b) compounds display single-molecule magnet behavior modulated by their spin ground state.