Ferromagnetic Polarization: The Quantum Picture of Switching On/Off Single-Molecule Magnetism

The mixed 3d–4f pentanuclear complex (Bu4N)­[MnIII4YIII(shi)4(OAc)4(CH3OH)4]·CH3OH·H2O (1) (H3shi = salicylhydroxamic acid) was synthesized by the direct reaction of Y­(NO3)3·6H2O, Mn­(OAc)2·4H2O, and H3shi. When an additional ligand, (NHBu3)3[W­(CN)8]·2H2O, was added, the mixed 3d–4f–5d hexanuclear complex (Et4N)5[MnIII4YIII(shi)4(OAc)4WV(CN)8]­(WO4)0.5 (2) was obtained. X-ray crystallographic analysis shows that the 3d–4f complex 1 represents a 12-metallacrown-4 (12-MC-4) structure, in which the metallacrown ring [Mn–N–O]4 connection captures one YIII ion with four bridging acetate anions, completing the eight-coordinated environment around YIII ion, while four methanol molecules each coordinate to the MnIII ions on the other side of the YIII ion. After octacyanotungstate is introduced, the [WV(CN)8] group substitutes for four methanol molecules of 1 to form complex 2. Magnetic studies indicate the overall antiferromagnetic coupling present within the MC ring of complex 1. However, interestingly, the dominant ferromagnetic coupling between MnIII ions was observed in complex 2. A susceptibility analysis shows that the natural spin alignments in 12-MC-4 metallacrowns are tuned from overall antiferromagnetic to dominant ferromagnetic fashions by magnetic coupling between MnIII ions and the WV ion. Complex 1 [MnIII4YIII] retains an S = 0 ground state, and complex 2 [MnIII4YIIIWV] shows obvious single-molecule magnet (SMM) behavior with an ST = 11/2 ground state, respectively, before and after introduction of the octacyanotungstate group. The spin frustration geometrical structure constructed by four MnIII ions and one WV ion was considered as the key factor for switching on the SMM properties of the 12-MC-4 system.