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.

一系列三价锰（MnIII）/二价镍（NiII）异金属簇合物，包括[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）以及[MnIII2NiII2(hmcH)2(pao)4(OMe)2(MeOH)2]·2H2O·6MeOH（4·2H2O·6MeOH）[其中paoH为吡啶-2-醛肟（pyridine-2-aldoxime），hmcH3为2,6-双(羟甲基)-对甲酚（2,6-Bis(hydroxymethyl)-p-cresol）]，通过二价锰盐与[Ni(paoH)2Cl2]、hmcH3以及三乙胺（NEt3）在有无叠氮化钠（NaN3）存在下反应制备并完成表征。配合物1具有MnIII4NiII5拓扑结构，可描述为两个共角的[Mn2Ni2O2]蝴蝶状单元，通过烷氧基桥连至一个外侧锰原子与一个外侧镍原子。配合物2具有与1类似的MnIII3NiII6拓扑结构，但将1中的两个共角[Mn2Ni2O2]单元替换为[Mn3NiO2]与[MnNi3O2]单元，且1中的外侧锰原子被镍原子取代。1与2是目前已报道的最大3d异金属/肟簇合物以及最大的MnIII-NiII簇合物。配合物3拥有[MnNi5(μ-N3)2(μ-OH)2]9+核心，其拓扑结构在离散分子中尚属首次被观测到。对1~3的结构进行细致分析后可知，配合物的Mn/Ni比例可能与不同桥联配体hmcH2–和/或N3–的存在相关。配合物4具有MnIII2NiII2缺陷双立方烷拓扑结构。对配合物1~4开展了变温固态直流与交流磁化率测试。对所得M/(NμB)随H/T变化的数据进行拟合，得到配合物1的S=5、g=1.94以及D=−0.38 cm–1，配合物3的S=3、g=2.05以及D=−0.86 cm–1。配合物2的基态通过交流数据确定，结果为S=5的基态。对于配合物4，基于三交换参数（3-J）模型拟合磁化率随温度变化的数据，得到其成对交换相互作用。配合物1表现出交流磁化率的异相信号，表明其可能为单分子磁体（Single Molecule Magnet，SMM）。