Synthesis, Structural Diversity, and Properties of Cd Metal–Organic Frameworks Based on 2-(5-Bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate and N-Heterocyclic Ancillary Ligands

Five 1–3D cadmium(II) coordination polymers, namely, [Cd(HL)(DMF)]n (1), [Cd4(HL)4(H2O)6]n (2), [Cd(HL)(phen)]n (3), [Cd2(HL)2(bpy)]n (4), and {[Cd3(HL)3(pbim)2]·H2O}n (5), have been synthesized and fully characterized [H3L = 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid, DMF = N,N-dimethylformamide, phen = 1,10-phenanthroline, bpy = 4,4′-bipyridine, and pbim = 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole)]. In those complexes, the doubly deprotonated H3L ligands and CdII ions display versatile coordination modes to construct various structures with interesting topologies. Complex 1 is a 2D helical structure with (4·82) topology built up from 3-connected (HL)2– and CdII nodes. Complex 2 containing (HL)2–-bridged tetranuclear CdII subunits is a 3D helical structure where both (HL)2– and CdII adopt three coordination modes to form a rare 3-connected network with (5·8·12)2(5·12·16)2(5·82)(82·12) topology. Substituting the smaller terminal ligands DMF and water with the larger terminal ligand p...