Anion influence on polymerization of Cd(II) picolinamide complexes

[Display omitted] •Cadmium(II) coordination polymers [CdX2(pia)]n (X = Cl, Br, I; pia = picolinamide).•Discrete complexes [Cd(SO4)(pia)(H2O)3]·2H2O and [Cd(pia)3(H2O)](NO3)(ClO4).•X-ray crystallography of the complexes.•Influence of anions on the structure. The reactions of picolinamide (pyridine-2-carboxamide, pia) with various cadmium(II) salts in aqueous media were investigated. With cadmium(II) halides, three novel coordination polymers (CPs) were isolated, namely: [CdX2(pia)]n (X = Cl (1), Br (2), I (3). Cadmium(II) sulphate gave [Cd(SO4)(pia)(H2O)3] ·2H2O (4) while cadmium(II) nitrate in the presence of perchlorate ions gave mixed complex [Cd(pia)3(H2O)](NO3)(ClO4) (5) with both anions acting as counterions. All isolated complexes were identified by chemical analysis and characterized using IR-spectroscopy and thermal methods (TG/DSC). X-ray crystal structure analysis of 1–3 revealed a distorted octahedral coordination of Cd(II) which consists of four halide and N,O-chelated pia ligands. The chain propagation is achieved through metal-halide double-bridges. The pia ligand is in cis geometry (cis-configured polymeric chain) and the topology of chains can be described as zig-zag. In 1 the neighbouring chains are mutually linked through weak CH···Cl and NH···Cl hydrogen bonds into 3D supramolecular framework. In 2 and 3, which are isostructural, unlike in 1 the neighbouring chains are linked by a strong head-to-head amide hydrogen bonds (graph set R22(8)) into supramolecular sheets in (0 1 0) planes and through weak CH···X interactions a 3D supramolecular framework is accomplished. In discrete molecules of 4 and 5, a distorted octahedral and pentagonal bipyramidal coordination of Cd(II) ion is revealed respectively. The final 3D supramolecular dimensionality of 4 and 5 is achieved through non-covalent interactions including sulphate ions in the former, and perchlorate and nitrate ions in the later thus pointing a discernible influence of anions on the structure.