Solvent-induced pore-size adjustment in the metal-organic framework [Mg3(ndc)3(dmf)4] (ndc = naphthalenedicarboxylate)

Two new compounds containing magnesium and the bidentate ligand 2,6-naphthalenedicarboxylate (ndc), namely [Mg(dmf)(2)(H2O)(4)]center dot ndc (1) (dmf = N,N-dimethylformamide) and [Mg-3(ndc)(3)(dmf)(4)] (TUDMOF-2) (2), have been obtained from Mg(NO3)(2)center dot 6H(2)0 and the pure acid using a solvothermal route. According to single-crystal X-ray studies both compounds are monoclinic. Complex 1 crystallizes in the space group P2(1)/c [a = 12.317(3), b = 12.582(2), c = 15.353(3) angstrom, beta = 110.96(3)degrees]. The compound consists of an isolated tetraaquabis-N,N-dimethylformamide cation and the deprotonated ligand with hydrogen bonds linking the cations and anions. The metal-organic framework 2 crystallizes in the space group C2/c [a = 13.451(3), b = 18.043(4), c = 20.937(5) angstrom, beta = 99.79(3)degrees] with trinuclear magnesium clusters connected to six dicarboxylate ligands that link the clusters into a three-dimensional network. In contrast to [Mg-3(ndc)(3)(def)(4)] (def = N,N-diethylformamide; 3), the dmf molecules coordinated to magnesium in TUDMOF-2 (2) not only cause a distortion of the network but induce accessibility for the adsorption of nitrogen. TUDMOF-2 has a Langmuir surface area of 520 m(2) g(-1) and a hydrogen adsorption capacity of 0.78 wt.-% at 77 K and 760 Torr.