New polymorph for Cd(II) chloro‑bridged coordination polymer based on 3-aminopyrazin-2-carboxylic acid: Synthesis, structural characterization, Hirshfeld surface analysis, thermal properties and molecular docking study on the antifungal activity

Abstract

A new polymorph of cadmium (II) coordination polymers, namely poly[[(3-aminopyrazin-4-ium-2-carboxylate-k2N1,O)di-μ-chlorido-cadmium(II)] monohydrate], {[CdCl2(C5H5N3O2)]-H2O}n, (PM2), is synthesized from the reaction of cadmium(II) chloride and 3-aminopyrazine-2-carboxylic acid (Hapca). The first P-1 polymorphic (PM1) has already been isolated; it was synthesized by the reaction of Hapca with the hydrated cadmium salt. Meanwhile, for the preparation of the new Pccn polymorph (PM2), the anhydrous metal salt was used. The two polymorphic Cd-based coordination polymers are synthesized in aqueous acidic media. To identify the potential protonation sites in the organic ligand Hapca and determine its coordinating ability, the ionization constants pKa are predicted using ACD/pKa and ChemAxon calculators. The new polymorph is characterized by single-crystal X-ray diffraction and show chloro-bridged zigzag chains with octahedrally coordinated metal ions where Hapca acts as a bidentate N/O chelating ligand. The chains are further interconnected via noncovalent interactions into three dimensional supramolecular networks. The dominant H···O and H···Cl interactions for both polymorphs were quantified using Hirshfeld surface analysis. The thermal properties of the two isolated polymorphic coordination polymers are also discussed. The antifungal activity of the two polymorphs PM1, PM2 and the organic free ligand Hapca against the yeast Candida albicans was screened by the molecular docking approach. The enzyme exo-β- (1,3)-glucanase (Exg) was chosen as a target. The drug-likeness activity and ADMET properties were also evaluated.