Hydrogen-bond-directed supramolecular assembly and interaction energy framework in a new dicopper(II) acetate–pyridine-4-carboxamide paddlewheel complex

Abstract A new solvated dicopper(II) paddlewheel complex, [Cu 2 (μ-OAc) 4 (4-pca) 4 ]·2DMF·2H 2 O, has been synthesized by slow solution crystallization and structurally characterized by single-crystal X-ray diffraction. The complex crystallizes in the triclinic space group P <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mover accent="true"> <m:mn>1</m:mn> <m:mo>̅</m:mo> </m:mover> </m:mrow> </m:math> $&amp;#x305;{1}$ and contains a centrosymmetric dicopper(II) paddlewheel unit located about a crystallographic inversion centre. The acetate ligands adopt the characteristic syn – syn carboxylate bridging mode, generating a classical Cu 2 (OAc) 4 core with axial coordination by pyridine-4-carboxamide ligands. The amide functionality promotes the formation of an extended supramolecular assembly through cooperative O–H⋯O, N–H⋯O and C–H⋯O hydrogen-bonding interactions together with π–π stacking between aromatic rings. Hirshfeld surface analysis reveals that H⋯H (41.6 %) and O⋯H/H⋯O (32.0 %) contacts dominate the molecular packing, while interaction energy framework calculations indicate significant dispersion and electrostatic contributions to lattice stabilization ( E tot = −207.4 kJ mol −1 ). FT-IR, Raman and UV–Vis spectroscopic analyses confirm coordination through acetate oxygen and pyridine nitrogen donors, supporting distorted square-pyramidal geometry around the Cu(II) centres. Density functional theory calculations reveal a relatively small HOMO–LUMO separation (0.816 eV), indicating appreciable electronic polarization within the coordination framework. Powder X-ray diffraction confirms phase purity and thermal analysis reveals stepwise solvent loss prior to decomposition of the paddlewheel framework.