Crystal structures, gas storage and magnetic properties of lanthanide-organic frameworks built up from dicarboxylates, [Ln2(2,5-pydc)2(2,5-pipdc)(H2O)2]n (Ln = Ce, Pr, Eu) and (H2pip)n[Ln2(2,6-pydc)4(H2O)2]n (Ln = Ce, Pr, Eu, Sm)

We have synthesized various kinds of lanthanide complexes, [Ln2(2,5-pydc)2(2,5-pipdc)(H2O)2]n (Ln = Ce (MOF 1), Pr (MOF 2), Eu (MOF 3); 2,5-pydc = 2,5-pyridinedicarboxylate, 2,5-pipdc = 2,5-piperazinedicarboxylate), and (H2pip)n[Ln2(2,6-pydc)4(H2O)2]n (Ln = Ce (MOF 4), Pr (MOF 5), Eu (MOF 6), Sm (MOF 7); 2,6-pydc = 2,6-pyridinedicarboxylate, H2pip = piperazinediium) under hydrothermal conditions. The X-ray crystallographic analysis shows that [Ln2(2,5-pydc)2(2,5-pipdc)(H2O)2]n forms three-dimensional coordination network, while (H2pip)n[Ln2(2,6-pydc)4(H2O)2]n forms one-dimensional coordination polymer, whose different coordination network structure is controlled by the positional isomer of pyridinedicarboxylate (2,5-pydc, 2,6-pydc). The magnetic properties and gas storage (H2 and CO2) capacities were also investigated, and among the synthesized compounds MOF 7 had the highest gas storage capacities for H2 and CO2. From the analysis of magnetic sus-ceptibility measurements, the Weiss constants for Ce, Pr, and Sm complexes were estimated. In the case of Pr complexes, MOF 2 and MOF 5, the magnetic susceptibility deviates from the Curie-Weiss law below 20 K and 10 K, respectively, which is the precursor phenomenon of antiferromagnetic ordering. In the case of Sm(III) com-plex, MOF 7, the magnetic susceptibility multiplied by temperature (chi T) as a function of temperature between 300 K and 2 K was theoretically analyzed and the spin-orbit coupling constant (lambda) and the energy levels of ground multiplet, 6HJ, were determined.