Crystal packing effects within [MnIII3O]7+ single-molecule magnets: Controlling intermolecular antiferromagnetic interactions

The reactions of 2-hydroxyphenylethanone oxime (Me-H2salox) and (2-hydroxy-phenyl)-phenyl-methanone oxime (Ph-H2salox) with Mn(ClO4)2·6H2O in MeOH afford trinuclear manganese complexes of [Mn3O(Me-salox)3(MeOH)3(ClO4)]·MeOH (1·MeOH) and [Mn3O(Ph-salox)3(MeOH)3(ClO4)]·2MeOH (2·2MeOH), respectively. X-ray analysis shows that both complexes contain a manganese triangle core, [MnIII3O]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 Mn3 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.

Graphical abstractTwo manganese triangle SMMs, [Mn3O(Me-salox)3(MeOH)3(ClO4)]·MeOH (1·MeOH) and [Mn3O(Ph-salox)3(MeOH)3(ClO4)]·2MeOH (2·2MeOH), have been synthesized and characterized structurally as a [MnIII3(μ3-O2−)]7+ core. The magnetic data indicate that both complexes 1 and 2 have an S = 6 spin ground state. The frequency-dependent out-of-phase signals AC and temperature-dependent and sweep-rate-dependent hysteresis loops are indicative of single-molecule magnet behavior. Both complexes represent obviously different quantum tunneling of mechanism resulting from their crystal packing.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two [MnIII3(μ3-O2−)]7+ triangle SMMs were synthesized and structurally characterized. ► Both complexes have an S = 6 spin ground state. ► They show the frequency-dependent AC and hysteresis loops indicative of single-molecule magnet behavior. ► Obviously different QTM mechanism resulting from their crystal packing.