Conformational Supramolecular Isomerism in Two-Dimensional Fluorescent Coordination Polymers Based on Flexible Tetracarboxylate Ligand

Six new coordination polymers, (Me2NH2)[In(L)]center dot DMF (1), (Me2NH2)(2)[In-2(L)(2)]center dot(DMF)(3)center dot(H2O)(2) (2), (Me2NH2)(4)[Cd-2(L)(2)]center dot(DMF)(2) (3), (Et2NH2)(2)[Cd(L)]center dot H2O (4), (Et2NH2)(3)[Cd-2(L)(2)]center dot(DEF)(2)center dot(H2O)(4) (5), (Et2NH2)(3)[Cd-2(L)(2)]center dot(EtNH2)(2)center dot(H2O)(2) (6) have been prepared based on a newly designed flexible tetracarboxylate ligand of H4L {H4L = 5-[bis(3-carboxybenzyl)amino]isophthalic acid; DMF = N,N-dimethylformamide; DEF = N,N-diethylformamide}. Compounds 1-6 possess very similar two-dimensional framework structures with (4,4)-net topology. These compounds comprise two groups of conformational supramolecular isomers, owing to identical compositions of the frameworks but different conformations of ligands. It is worth noting that as much as seven pairs of stereoisomers of ligands have been found in these compounds, which demonstrated that the introduction of multiple single bonds has greatly expanded the flexibility of the ligand. The photoluminescent properties of compounds 1-6 have also been investigated where the emission of these supramolecular isomers are from blue to green.