Six new calcium metal−organic frameworks [Ca(BDC)(DMF)(H2O)] (1), [Ca(ABDC)(DMF)] (2), [Ca3(BTC)2(DMF)2(H2O)2]·3H2O (3), [Ca(H2dhtp)(DMF)] (4), [Ca(H2dhtp)(DMF)2] (5), and one modification of [Ca(H2dhtp)2(H2O)2] (6), (DMF = N,N-dimethylformamide; BDC = 1,4-benzenedicarboxylate anion; ABDC = 2-aminobenzene-1,4-dicarboxylate anion; BTC = 1,3,5-benzenetricarboxylate anion; H2dhtp = 2,5-dihydroxyterephthalate anion) were synthesized from calcium ions and aromatic carboxylic acids by solvothermal reactions and microwave-assisted solvothermal reactions. The single crystal structure analysis showed that all complexes display three-dimensional structures containing various inorganic motifs with helical or straight one-dimensional inorganic chains (1−3), pentagonal bipyramidal dimers (4 and 6), or discrete octahedra (5) connected through organic linkers and forming DMF- or water-coordinated neutral frameworks. It is also interesting that compounds 1−5 undergo dissolution/reorganization reactions comprising a break and reformation of the Ca−O bond and leading to destruction/construction structural transformations. Compounds 1−5 were further characterized by thermal gravimetric analysis, powder X-ray diffraction, UV−vis, infrared, and PL spectroscopy.

8 ] (3) (BTEC ¼ 1,2,4,5-benzenetetracarboxylate anion), were synthesized from magnesium nitrate and 1,2,4,5-benzenetetracarboxylic acid with variable ratios of organic base under microwave-assisted solvothermal reactions at the temperature of 180 (1) or 150 C (2 and 3). The results from crystal structure analysis showed that 1 was a 3D metal-organic framework, 2 a 2D layer, and 3 a 1D ladder structure. In addition, heating 1 at the temperature of 150 C would convert it to 1a which can be a novel single-crystal-to-single-crystal transformation of coordination polymer. Single crystal of 1a has a new 3D structure with formula [Mg 15 (BTEC) 6 (HBTEC) 2 (H 2 O) 12 ]$4H 2 O, containing unsaturated magnesium sites. Further gas adsorption experiments revealed that 1a undergoes a highly selective sorption of hydrogen instead of nitrogen gases. Photoluminescence studies also displayed that 1a emits extra strong green luminescence around 510 nm under the excitation of ultraviolet light. Experimental Materials and general methodsAll reagents and solvents for syntheses were purchased from commercial sources and used as received. Microwave-assisted

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The solvothermal reaction of magnesium nitrate with bi­phenyl-4,4′-dicarboxylic acid in N,N-dimethyl­formamide and water leads to the formation of crystals of the title complex, [Mg(C14H8O4)(H2O)2]n. In the crystal structure, the Mg cations are coordinated by six O atoms from two water mol­ecules and four symmetry-related biphenyl-4,4′-dicarboxyl­ate anions within slightly distorted octa­hedra. The Mg cations are located on a center of inversion, the biphenyl-4,4′-dicarboxyl­ate anions around a twofold rotation axis and the water mol­ecule in a general position. The Mg cations are linked by the anions into a three-dimensional framework.