Different Phenomena in Magnetic/Electrical Properties of Co(II) and Ni(II) Isomorphous MOFs

[Image: see text] Two unprecedented and stable metal–organic frameworks, {[Co(2)(H(2)O)(2)(L)(OH)]·2.5H(2)O·0.5DMF}(n) (1) and {[Ni(2)(H(2)O)(2)(L)(OH)]·1.75H(2)O}(n) (2), have been synthesized (H(3)L = 5-(5-carboxy-pyridin-3-yloxy)-isophthalic acid, DMF = N,N-dimethylformamide). Structural analysis shows that 1 and 2 are heteronuclear isomorphous, possessing a three-dimensional (3D) (4,8)-connected flu/fluorite topological framework formed through the interconnection of tetranuclear butterfly {M(4)(COO)(6)(OH)(2)} clusters and the ligands. Although the frameworks of these two compounds are similar, their magnetic properties are different. Compound 1 exhibits an antiferromagnetic interaction in the high-temperature region, while 2 shows a weak ferromagnetic interaction in the whole-temperature region. Furthermore, considering the presence of hydroxyl groups and water molecules in the frameworks, we tested their proton conductivity. The efficient proton transfer pathway in the framework endowed 1 and 2 with excellent proton conductivities of 9.07 × 10(–5) and 1.29 × 10(–4) S·cm(–1) at 363 K and 98% relative humidity (RH), respectively.