Homochiral coordination polymers constructed from aminocarboxylate derivates: Effect of bipyridine on the amidation reaction

Using aminocarboxylate derivates (S)-N-(4-cyanobenzoic)-glutamic acid (denoted as cbg, 1a) and (S)-N-(4-nitrobenzoic)-glutamic acid (denoted as nbg, 1b) as chiral ligands, five new homochiral coordination polymers formulated as [Cu(cbg)(H2O)2]n (3), [Cu(cbop)2(4,4′-bipy)(H2O)]n (4) (cbop=(S)-N-(4-cyanobenzoic)-5-oxoproline, 4,4′-bipy=4,4′-bipyridine), {[Cu(nbop)2(4,4′-bipy)]·4H2O}n (5) (nbop=(S)-N-(4-nitrobenzoic)-5-oxoproline), {[Cd(nbop)2(4,4′-bipy)]·2H2O}n (6), and [Ni(nbop)2(4,4′-bipy)(H2O)2]n (7) have been hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction study reveals that the original chirality of aminocarboxylate derivates is maintained in all these complexes. Complexes 3, 4, and 7 are one-dimensional infinite chain coordination polymers, while complexes 5 and 6 possess two-dimensional network structures. In situ cyclization of 1a and 1b was taken place in the formation of complexes 4–7, which may be due to the competition of 4,4′-bipyridine with chiral ligands during the coordination process. Preliminary optical behavior investigation indicates that ligands 1a, 1b, and complexes 6, 7 are nonlinear optical active.