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