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

Two unprecedented
and stable metal–organic frameworks, {[Co2(H2O)2(L)­(OH)]·2.5H2O·0.5DMF}n (1) and
{[Ni2(H2O)2(L)­(OH)]·1.75H2O}n (2), have been
synthesized (H3L = 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 {M4(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.