Exploring three stable penta-coordinated multinuclear Cu(II) bis (salamo)-based complexes

Penta-coordinated homo-binuclear [Cu2(L)(CH3OH)]ClO4?CH3OH (1), [Cu2(L)(CH3CH2OH)]ClO4 (2) and homotetranuclear [{Cu2(HL)Cl(?-Cl)}2]?2CHCl3 (3) complexes containing a symmetrical multi-halogen-substituted bis (salamo)-based ligand H3L have been successfully synthesized and characterized by elemental analyses, FT-IR and UV?Vis absorption spectroscopy, Hirshfeld surfaces analyses and density functional theory (DFT) calculations. The crystal structures of the three Cu(II) complexes were determined by single crystal X-ray crystallography. All the Cu(II) atoms in the binuclear complexes 1 and 2 are located in the N2O2 cavities of the fully deprotonated (L)3- unit, and penta-coordinated with slightly distorted square pyramidal geometries. Methanol and ethanol molecules are coordinated to the Cu(II) atoms in the complexes 1 and 2, respectively. Most surprisingly, the complex 3 has a novel penta-coordinated tetranuclear structure unreported earlier. The four Cu(II) atoms in the complex 3 are all penta-coordinated, and the geometries around the Cu(II) centers in complexes 3 are square pyramid. It is worth noting that two binuclear [Cu2(HL)Cl] units are connected to two bridged chloride ions and the complex 3 has a crystallographically imposed inversion center at the midpoint of Cu2 and Cu2#1. The supramolecular structures of the complexes 1, 2 and 3 are formed by inter-molecular interactions. In addition, Hirshfeld surfaces analyses showed short-range interactions on the molecular surfaces of the complexes 1, 2 and 3. Furthermore, the fluorescence properties of H3L and its three Cu(II) complexes are also discussed.

Automated summary

The study successfully synthesized and characterized three copper complexes containing a multi-halogen-substituted bis (salamo)-based ligand H3L. These complexes exhibit different molecular structures and coordination environments, as well as complex supramolecular structures and unique fluorescence properties.