Supramolecular architectures of mononuclear nickel(II) and homobinuclear copper(II) complexes with the 5,5′-dimethyl-2,2′-bipyridine ligand: Syntheses, crystal structures and Hirshfeld surface analyses

Abstract Two new compounds based on one mononuclear nickel(II) and one homobinuclear copper(II) complexes respectively and of general formula [Ni(dmbpy)2(CH3COO)]ClO4 (1) and [Cu2(dmbpy)2(CH3COO)3]ClO4 (2) with dmbpy = 5,5′-dimethyl-2,2′-bipyridine, were synthesized by hydrothermal treatment. Both were influenced by the coordinated acetate ion molecule. The crystal and molecular structures of (1) and (2) were determined by single crystal X-ray diffraction method and both compounds were additionally characterized by means of elemental and thermogravimetric analysis, FT-IR spectroscopy, powder X-ray diffraction and UV–visible. The mononuclear complex (1) shows a distorted octahedral geometry around the metal ion. On the other hand, the copper(II) compound crystallizes as an homobinuclear system, in which each of the metal ions is located into the N2O3 coordination spheres adopting a distorted square pyramidal geometry. In (2) the intramolecular distance between two copper atoms is of the order of Cu1-Cu2 = 3.38 (2) A. In both crystals packing of these two complexes, H-bonding, π⋯π, and C-H⋯π interactions are operative in forming supramolecular motifs. Complex (1) displays two 1D chains that lead to form R 8 8 ( 42 ) ring motifs, repetition of which generates a 2D supramolecular network. These chains interacts with the neighbouring ones via intermolecular C-H···π and π···π stacking interactions, leading to the formation of a 3D-stacking network (2D+1D→3D). Formation of a 2D supramolecular sheet in the solid state structure of (2) is facilitated by the C–H⋯O, C–H⋯π and π⋯π interactions (1D+1D→2D). Hirshfeld surface analysis and theoretical calculations were carried out on the two compounds. The results clearly show that C–H···O, C–H··· π and π···π stacking interactions play a paramount role in the stabilization of the supramolecular architecture of (1) and (2). In addition, absorption spectra reveal their semi-conductive nature (4.19 eV for (1)·and 4.43 eV for (2)).