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

Six
new coordination polymers, (Me2NH2)­[In­(L)]·DMF
(1), (Me2NH2)2[In2(L)2]·(DMF)3·(H2O)2 (2), (Me2NH2)4[Cd2(L)2]·(DMF)2 (3), (Et2NH2)2[Cd­(L)]·H2O (4), (Et2NH2)3[Cd2(L)2]·(DEF)2·(H2O)4 (5), (Et2NH2)3[Cd2(L)2]·(EtNH2)2·(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.