Single-Molecule Magnet Behavior in Heterometallic M~(II)-Mn_2~(III)-M~(II)Tetramers(M~(II)= Cu,Ni)Containing Mn~(III)Salen-Type Dinuclear Core

摘要

The linear-type heterometallic tetramers,[Mn_2~(III)(5-MeOsaltmen)_2M_2~(II)(L)2](CF3SO3)_2·2H2O(M~(II)= Cu,1a;Ni,2a),where 5-MeOsaltmen~(2-)= 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 P2_1 space group.The structure has a [M~(II)-NO-Mn~(III)-(O)2-Mn~(III)-ON-M~(II)] skeleton,where-NO-is a linking oximato group derived from the non-symmetrical Schiff-base complex [M~(II)(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 P2_1/c space group without significant changes in their structures in comparison to 1a and 2a.Magnetic measurements on 1a and 1b revealed antiferromagnetic Mn~(III)-Cu~(II)interactions via the oximato group and weak ferromagnetic Mn~(III)...Mn~(III)interactions via the biphenolato bridge leading to an S_T = 3 ground state.On the other hand,the diamagnetic nature of the square planar Ni~(II)center generates an S_T = 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.