Solvent-Dependent Structural Variation of Zinc(II) Coordination Polymers and Their Catalytic Activity in the Knoevenagel Condensation Reaction

The novel self-assembled zinc­(II) coordination polymers [Zn­(L)­(H₂O)₂]_n (1), [Zn­(L)­(H₂O)₂]_n­·n(formamide) (2), [Zn­(L)­(H₂O)₂]_n­·n(N-methylformamide) (3), [Zn­(L)­(H₂O)­(formamide)]_n (4), and [Zn₃(L)₂­(formate)₂­(4,4′-bipyridine)₃]_n­·2n(DMF)­·2n(H₂O) (5) (L = 5-acetamidoisophthalate) have been synthesized and characterized by elemental microanalysis, infrared spectroscopy, thermogravimetric analysis, and X-ray single crystal X-ray diffraction. 1, 2, and 3 are one-dimensional (1D) coordination polymers that crystallize in monoclinic P2₁, monoclinic P2₁/m, and triclinic P1̅ systems, respectively, and are pseudo-polymorphic supramolecular isomers with 1 having a helical arrangement, and 2 and 3 exhibiting zigzag type structures containing different guest molecules. Compound 4 crystallizes in the triclinic P1̅ space group and is a 1D coordination polymer that exhibits fused 8-membered and 16-membered dimetallic rings. Compound 5 features a two-dimensional network type polymer with trimetallic cores. Compounds 1–5 expand to three-dimensional by means of H-bond interactions. These coordination polymers act as effective heterogeneous catalysts, under mild conditions, for the Knoevenagel condensation reaction of different aldehydes with an active methylene compound (malononitrile) and can be recycled without losing activity.