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.

Graphical abstractDepending on the substituted sites of the carboxylate group on the benzene ring of the ligands, either 2D (6, 3) or (4, 8) net was obtained through the assemble reactions between series of new rigid imidazolate/carboxylate functionalized ligands and Zn2+/Cd2+/Cu2+ ions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Rigid imidazolate/carboxylate functionalized ligand. ► Effect of the torsion of the ligands on crystal structures and properties. ► High thermal stability.