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.