Crystal packing effects within [Mn ~III _3O] ~(7+) single-molecule magnets: Controlling intermolecular antiferromagnetic interactions

摘要

The reactions of 2-hydroxyphenylethanone oxime (Me-H _2salox) and (2-hydroxy-phenyl)-phenyl-methanone oxime (Ph-H _2salox) with Mn(ClO _4) _2·6H _2O in MeOH afford trinuclear manganese complexes of [Mn _3O(Me-salox) _3(MeOH) _3(ClO _4)]·MeOH (1·MeOH) and [Mn _3O(Ph-salox) _3(MeOH) _3(ClO _4)] ·2MeOH (2·2MeOH), respectively. X-ray analysis shows that both complexes contain a manganese triangle core, [Mn ~III _3O] ~(7+). The structural distortion from the twisting of the oxime ligands dominates the ferromagnetic interactions within the three Mn ions in both compounds and results in an S = 6 ground state. The frequency dependence of out-of-phase signals in the alternating current (AC) magnetic susceptibility measurements and the temperature-dependent and sweep-rate-dependent hysteresis loops are indicative of single-molecule magnet behavior. Moreover, both complexes show step-wise magnetization, indicating the occurrence of quantum tunneling of magnetization (QTM). Interestingly, a tail to tail arrangement in the crystal packing of complex 1·MeOH results in strong intermolecular H-bonding interactions and leads to the exchange-bias effect from the antiferromagnetic interaction between the adjacent Mn _3 molecules. In contract, QTM steps of complex 2·2MeOH show an absence of the exchange-bias effect due to a weak intermolecular interaction from a head to tail arrangement.