Synthesis, Crystal Structures, Hirshfeld Surface Analysis, Computational Investigations, Thermal Properties, and Electrochemical Analysis of Two New Cu(II) and Co(II) Coordination Polymers with the Ligand 5-Methyl-1-(pyridine-4-yl-methyl)-1H-1,2,3-triazole-4-carboxylate.

Two new Cu(II) (CP1) and Co(II) (CP2) coordination polymers (CPs) with the triazole ligand 5-methyl-1-(pyridin-4-yl-methyl)-1H-1,2,3-triazole-4-carboxylate (L1) have been synthesized and structurally characterized by SCXRD (Single Crystal X-Ray Difraccion), PXRD (Power X-Ray Difracction), FT-IR (Fourier Transform Infrared), TG (Theermo Gravimetric), and electrochemical techniques. Both CPs were obtained at the water/n-butanol interface by reacting nitrate salts of each metal with the NaL1 ligand. SCXRD analysis revealed that CP1 (Coordination Polymer 1) and CP2 (Coordination Polymer 2) crystallize in the monoclinic space groups C2/c (No. 15) and P21/n (No. 14), respectively, forming 1D zigzag chain structures, which further lead to a 2D supramolecular network through O-H⋯O and C-H⋯O hydrogen bond interactions, respectively. In CP1, the supramolecular structure is assembled by hydrogen bonds involving water molecules. In contrast, CP2 forms its supramolecular network mainly through hydrogen bonds between adjacent triazole ligand molecules. Hirshfeld surface analysis revealed that the most significant contributions to the crystal packing come from H⋯O/O⋯H, H⋯H, H⋯N/N⋯H, and H⋯C/C⋯H interactions. In addition, FT-IR provided information on the functional groups involved in the coordination, while the decomposition patterns of both CPs were evaluated by TGA. Electrochemical studies conducted in a saline environment showed that CP1 exhibits superior hydrogen evolution reaction (HER) kinetics compared to CP2, as evidenced by a higher exchange current density and a lower Tafel slope. Density functional theory calculations and experimental bandgap measurements provided a deeper understanding of the electronic properties influencing the electrochemical behavior. The results highlight the potential of CP1 as an efficient catalyst for HER under saline conditions.