Framework materials assembled from magnesium carboxylate building units

Four coordination polymers containing magnesium metal nodes and di-or tricarboxylic acid organic connectors have been synthesised and structurally characterised with the aid of single crystal X-ray diffraction. Mg-3(bdc)(3)(DMA)(4) (1) andMg(3)(bdc)(3)(EtOH)(2) (2) were prepared from the 1 : 1 reaction of 1,4-benzenedicarboxylic acid (H(2)bdc) with Mg(NO3)(2)center dot 6H(2)O in dimethylacetamide (DMA) or EtOH respectively. Both 1 and 2 contain tri-metallic magnesium carboxylate units which act as six-coordinate nodes for network construction. These tri-magnesium nodes are joined by the bdc ligands in 1 to give a 2D layered structure with coordinated DMA solvent molecules between the layers, whereas in 2 they stack end-on to form a novel 3D network containing 1D Mg carboxylate chains. Both 1 and 2 are moderately hygroscopic, and powder X-ray diffraction and thermogravimetric analysis studies show them to be interconvertible with Mg(bdc) and the hydrated complex Mg(bdc)(H2O) 2 via a series of solid-state reactions. Reaction of magnesium nitrate with 4,4 '-biphenyldicarboxylic acid (H(2)bpdc) in DMA gives Mg-3(bpdc)(3)(DMA)(4) (3), which in contrast to 2 forms a 'squashed' 3D cubic network as a result of the increased distance between the trinuclear nodes necessitated by the longer bpdc ligands. Reaction of magnesium nitrate with the triangular organic building block 1,3,5-tricarboxylic acid (H(3)btc) in DMA gives crystals of Mg(H(1.5)btc)(2/3)(btc)(1/3)(DMA)(2)center dot(DMA)(1/3) (4). Compound 4 contains mono-metallic metal nodes which assemble with the btc ligands to give 2D 63 tessellated layers with Mg-coordinated DMA molecules lying perpendicular to the layers. Some free DMA is also present in 4, sited in small pores between the layers.