Toward the Recognition of Enolates/Dicarboxylates: Syntheses and X-ray Crystal Structures of Supramolecular Architectures of Zn(II)/Cd(II) Using 2,2‘-Biimidazole

Six coordination complexes, {[M(H2biim)2(H2O)2]2+X2-}·(nH2O) [(H2biim = biimidazole); {M = Zn (1), Cd (2);
X = squarate; n = 2}; {M = Zn (3), Cd (4); X = glutarate; n = 4}; {M = Zn (5), X = succinate; n = 4}; {M = Cd (6), X =
succinate; n = 2}], have been synthesized and characterized by X-ray single-crystal structure determination. The crystal packing of
all the complexes reveals that cationic [M(H2biim)2(H2O)2]2+ fragments are self-assembled by recognition of enolate/dicarboxylate
anions by the uncoordinated N−H motif of H2biim resulting in one-dimensional supramolecular ribbons. The parallel ribbons are
stitched across by water-mediated hydrogen bonding and π−π interactions leading to two types of topology:  one is a two-dimensional
brick wall (1, 2, 6), and the other is a three-dimensional architecture (3−5). In two structures (1, 2) interesting “sandwiched” π−π
interactions were observed.