New polymorphs of magnesium-based metal-organic frameworks Mg3(ndC)3 (ndc=2,6-naphthalenedicarboxylate)

Two new magnesium 2,6-naphthalenedicarboxylate (ndc) metal-organic frameworks, [Mg-3(ndc)(3)(dif)(4)] (1) (dif = N,Ndiisopropylformamide) and [Mg-3(ndc)(3)(dmf)(2)(CH3OH)(H2O)](dmf) (2 = TUDMOF-3) (dmf = N,N-dimethylformamide), have been synthesised under solvothermal conditions from Mg(NO3)(2)center dot 6H(2)O and pure 2,6-naphthalenedicarboxylic acid. According to single-crystal X-ray crystallographic studies, complex I crystallises in the space group P2(1)/n [a = 14.769(3) angstrom, b = 13.325(3) angstrom, c = 17.998(4) angstrom, beta = 108.67(2)degrees] and complex 2 in the space group P (1) over bar [a = 11.1116(11)angstrom, b = 12.6229(13)angstrom, c = 17.800(2)angstrom, a 88.568(14)degrees, beta = 83.833(13)degrees, gamma= 70.167(11)degrees]. The structures of compounds I and 2 consist of trinuclear magnesium clusters connected to six dicarboxylate ligands; for 2, the clusters act as distorted octahedral nodes to give a 3D network. In contrast, the trinuclear clusters in I act as pseudo-planar-hexagonal nodes to give a 2D network assembly. According to nitrogen and hydrogen physisorption measurements at 77 K for compounds I and 2, TUDMOF-3 has a permanent porosity with a Langmuir surface area of 632 m(2)g(-1), a specific pore volume of 0.21 cm(3)g(-1) and a hydrogen storage capacity of 1.23 wt.-% at 77 K and 1 bar, whereas compound 1 is not porous. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).