1D chains, 2D networks and 3D interdigitated frameworks of isoorotic acid or 4,4′-bipyridyl and isoorotic acid: syntheses, structures, and sorption properties

Abstract

Five new coordination polymers, {[Cu(H₂iso)₂]·2H₂O}_n (1), {Mn(Hiso)(H₂O)₃}_n (2), {Mn(Hiso)(H₂O)₂}_n (3), {[Cu(Hiso)(4,4′-bipy)(H₂O)]·2H₂O}_n (4) and {[Ni(Hiso)(4,4′-bipy)(H₂O)}]·0.5(4,4′-bipy)}_n (5) (H₃iso = 2,4-dihydroxypyrimidine-5-carboxylic acid or isoorotic acid; 4,4′-bipy = 4,4′-bipyridyl), have been synthesized using hydrothermal as well as room temperature solvent diffusion techniques and structurally characterized. Compounds 1 and 2 are 1D coordination polymers which are further connected by O–H⋯N, O–H⋯O hydrogen bonding interactions forming 3D supramolecular frameworks. Compound 3 is a 2D coordination polymer where 1D chains of {Mn(Hiso)(H₂O)₂} are linked by an oxo (μ₂-O) bridge. Compound 4 consists of isoorotic acid and 4,4′-bipy, a mixed linker system. It forms a 2D sheet like extended structure and these sheets stack on each other to give a 3D supramolecular porous structure. In case of 5, Ni(Hiso) 1D chains are bridged by 4,4′-bipy forming a 2D network and networks are further interdigitated through hydrogen bonding interactions resulting in a 3D supramolecular framework with a 1D channel where 4,4′-bipy molecules are accommodated as guests. Compound 5 undergoes a structural contraction after the removal of the guest 4,4′-bipy and metal bound water molecules and shows a non-porous behaviour toward N₂ at 77 K. However, at 195 K, it shows a stepwise uptake for both CO₂ and C₂H₂, suggesting the flexible nature and polar pore surface of the framework.