Syntheses and characterization of four 2D metal–organic networks based on rigid imidazolate/carboxylate functionalized ligand – Effect of the torsion of the ligands on crystal structures and properties

A series of rigid imidazolate/carboxylate functionalized ligands, X-(5,7-dioxopyrrolo[3,4-f]benzimidazole-6-yl)benzoic acid (X = 4, H24-DPBB; X = 3, H23-DPBB; X = 2, H22-DPBB) were designed and used for the assemble reactions with Zn2+/Cd2+/Cu2+ ions. Four compounds, [Zn(4-DPBB)(H2O)]·DMSO·0.5MeOH (1), [Cd(3-DPBB)(DMA)1.8(H2O)0.2] (2), [Cu(3-DPBB)(DMSO)(DMA)] (3) and [Cd(2-DPBB)(DMA)2] (4) have been synthesized and structurally characterized (where DMSO = dimethylsulfoxide, DMA = dimethyl acetylamide). Single crystal X-ray analyses show that the four compounds are all based on 3-connected single metal nodes and 3-connected spacers. Compounds 1 and 2 bear a 2D (6, 3)-net structure, while 3 and 4 have a 2D (4, 8)-net. Compared with 2, 3 and 4, 1 exhibits a relatively high thermal stability which is up to ∼550 °C. Luminescent analysis indicates that 1 and 2 exhibit linker-localized emissions while 4 has ligand-to-metal charge transfer (LMCT) emission. The effect of the torsion of the ligands on the crystal structures and properties of the four compounds is discussed.