Studies on two phenoxo-bridged homopolynuclear Cu(II) bis(salamo) type complexes based on theoretical calculations and fluorescence properties

The dinuclear Cu(II) complex [Cu-2(HL)Br-2(MeOH)]center dot MeOH (1) and the tetranuclear Cu(II) complex [Cu-4(L)(2)] (ClO4) (2)center dot 2EtOH (2), based on a new bis(salamo) type ligand H3L, have been successfully self-assembled and structurally characterized by X-ray single crystal diffraction experiments. In complex 1, the partially deprotonated ligand unit (HL)(2-) is coordinated with the Cu(II) ions. It is noteworthy that two bromine ions and one methanol molecule with balanced charges are involved in the coordination. Both central coordination Cu(II) ions are five-coordinated. Finally, complex 1 can form a two-dimensional planar network structure and a one-dimensional chain-like structure through intermolecular hydrogen bonds and C-H pi interactions, respectively. Meanwhile, complex 2 has a centrosymmetric structure with two phenolic oxygen atoms bridging two molecules of metallized ligand [Cu-2(L)] units, where Cu1 is five-coordinated and Cu2 is four-coordinated. Thus, complex 2 forms a three-dimensional superamolecular network structure and a one-dimensional chain-like structure through intermolecular hydrogen bonds and pi-pi stacking interactions, respectively. The energy gaps between the HOMO and LUMO orbitals of complexes 1 and 2 were investigated by DFT calculations, indicating that the complexes are stable. The interaction sites of the ligand with the Cu2+ ions were examined by ESP investigation, and the results are consistent with the crystal structure. The weak intermolecular interaction forces of complexes 1 and 2 were explored by Hirshfeld surfaces and IRI analyses. The luminescent properties of complexes 1 and 2 were illustrated by fluorescence spectroscopy research.

Automated summary

In this study, two Cu(II) complexes based on a new bis(salamo) ligand were successfully synthesized and characterized. Complex 1 is a dinuclear complex with a two-dimensional and one-dimensional network structure, while complex 2 is a tetranuclear complex with a three-dimensional and one-dimensional network structure. DFT calculations confirmed the stability of both complexes, and fluorescence spectroscopy research illustrated their luminescent properties.