Auxiliary ligand-controlled supramolecular assembly of three Cd(ii) coordination polymers based on a (E)-3-(quinolin-4-yl) acrylic acid: syntheses, structures and photoluminescent properties

Abstract

Reactions of deprotonated (E)-3-(quinolin-4-yl) acrylic acid (QCA) with nitrates of cadmium, in the presence or absence of auxiliary 4,4′-bipyridine (4,4′-bipy) ligand in CH₃OH–DMF–H₂O, produce three novel compounds with the formula of [Cd(QCA)₂(H₂O)]_n (1), [Cd(QCA)₂(4,4′-bipy)]_n (2) and{[Cd(QCA)₂(4,4′-bipy)_1.5]·2.5H₂O}_n (3). Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, thermogravimetric (TGA) and powder X-ray diffraction (PXRD) analysis. Compounds 1 and 2 displays 2D undulated and planar layered structures respectively, which are further connected by intermolecular hydrogen bonds to form a 3D supramolecular architecture. In compound 3, QCA and 4,4′-bipy ligands link Cd centers to generate 1D ladder-like chain. An unusual uudd cyclic water tetramer in the crystal lattice of 3 is observed as the second example reported until now. Obviously, the structural differences among them are attributable to the different molar ratio of QCA to auxiliary 4,4′-bipy ligand. Moreover, the photoluminescent properties of all the compounds have been investigated.