Cubic networks and 3 6 tilings assembled from isostructural trimeric magnesium aryldicarboxylates

Abstract

Two new metal-organic frameworks [{Mg₃(bpdc)₃·4DMF}⊃3.8DMF] (1), and [Mg₃(bdc)₃·4DMSO] (2) have been synthesized by the high temperature equimolar reactions of magnesium nitrate with the appropriate dicarboxylic acid in either neat DMF or mixed DMF/DMSO solutions (where bpdcH₂=4,4′-biphenyldicarboxylic acid and bdcH₂=1,4-benzenedicarboxylic acid). The crystal structures of 1 and 2 were determined by X-ray analyses and found to be similarly composed of linked trimeric secondary building units. The trimers in 1 act as distorted octahedral nodes to produce a three-dimensional cubic network with guest DMF molecules trapped within square channels. In contrast, the trimeric SBUs in 2 act as pseudoplanar-hexagonal nodes to give an unusual 3⁶ two-dimensional network assembly. Compound 1 is potentially porous and thermogravimetric analysis is consistent with the initial loss of guest DMF and framework-bound DMF in two steps between 68 – 330°C, with decomposition of the material at 580°C.