Syntheses, Structures, and Magnetic Properties of a Family of Tetra-, Hexa-, and Nonanuclear Mn/Ni Heterometallic Clusters

A family of MnIII/NiII heterometallic clusters, [MnIII4NiII5(OH)4(hmcH)4(pao)8Cl2]·5DMF (1·5DMF), [MnIII3NiII6(N3)2(pao)10(hmcH)2(OH)4]Br·2MeOH·9H2O (2·2MeOH·9H2O), [MnIIINiII5(N3)4(pao)6(paoH)2(OH)2](ClO4)·MeOH·3H2O (3·MeOH·3H2O), and [MnIII2NiII2(hmcH)2(pao)4(OMe)2(MeOH)2]·2H2O·6MeOH (4·2H2O·6MeOH) [paoH = pyridine-2-aldoxime, hmcH3 = 2, 6-Bis(hydroxymethyl)-p-cresol], has been prepared by reactions of Mn(II) salts with [Ni(paoH)2Cl2], hmcH3, and NEt3 in the presence or absence of NaN3 and characterized. Complex 1 has a MnIII4NiII5 topology which can be described as two corner-sharing [Mn2Ni2O2] butterfly units bridged to an outer Mn atom and a Ni atom through alkoxide groups. Complex 2 has a MnIII3NiII6 topology that is similar to that of 1 but with two corner-sharing [Mn2Ni2O2] units of 1 replaced with [Mn3NiO2] and [MnNi3O2] units as well as the outer Mn atom of 1 substituted by a Ni atom. 1 and 2 represent the largest 3d heterometal/oxime clusters and the biggest MnIIINiII clusters discovered to date. Complex 3 possesses a [MnNi5(μ-N3)2(μ-OH)2]9+ core, whose topology is observed for the first time in a discrete molecule. Careful examination of the structures of 1–3 indicates that the Mn/Ni ratios of the complexes are likely associated with the presence of the different coligands hmcH2– and/or N3–. Complex 4 has a MnIII2NiII2 defective double-cubane topology. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1–4. Fitting of the obtained M/(NμB) vs H/T data gave S = 5, g = 1.94, and D = −0.38 cm–1 for 1 and S = 3, g = 2.05, and D = −0.86 cm–1 for 3. The ground state for 2 was determined from ac data, which indicated an S = 5 ground state. For 4, the pairwise exchange interactions were determined by fitting the susceptibility data vs T based on a 3-J model. Complex 1 exhibits out-of-phase ac susceptibility signals, indicating it may be a SMM.