Mixed-ligand Сu(II) complex based on m-hydroxybenzoate and nicotinamide: Synthesis, crystal structure and Hirshfeld surface analysis

A mixed-ligand Cu(II) complex containing m-hydroxybenzoate and nicotinamide ligands was synthesized and characterized by elemental analysis, FTIR spectroscopy, UV–visible spectroscopy, single-crystal X-ray diffraction and Hirshfeld surface analysis. Single-crystal X-ray diffraction revealed that the complex crystallizes in the monoclinic system with space group P2 1 /n. The Cu(II) center adopts a distorted octahedral coordination environment formed by carboxylate oxygen atoms from m-hydroxybenzoate ligands, pyridine nitrogen atoms from nicotinamide ligands, and coordinated water molecules. FTIR analysis confirmed deprotonation of the carboxylic acid group and coordination of the carboxylate group in a monodentate mode, while the spectral shift of pyridine-ring vibrations indicated coordination of nicotinamide through the pyridine nitrogen atom. UV–visible spectral changes further supported complex formation and the modification of the ligand's electronic environment upon coordination to Cu(II). The crystal packing is stabilized by O–H···O and N–H···O hydrogen bonds involving hydroxyl and amide groups, as well as coordinated water molecules. Hirshfeld surface and fingerprint analyses indicated that H···H and O···H/H···O contacts make the largest contributions to the supramolecular architecture, with O···H/H···O interactions corresponding to the principal hydrogen-bonding contacts. These results provide structural insight into the coordination behavior and supramolecular organization of Cu(II) mixed-ligand complexes based on hydroxybenzoate and nicotinamide ligands.

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