Studying anion-dependent paradoxically fluorescent Cu(II) complexes bearing a pyridine-decorated tetradentate half-salamo-like ligand

A new pyridine-decorated half-salamo-like ligand (HL) was designed and synthesized by a one-pot method. Based on this ligand, the single crystals of three anion-dependent Cu(II) complexes [Cu(L)Cl]center dot CH3OH (1), [Cu(L)Br] (2) and [Cu(L)(NO3)] (3) have been cultivated successfully and the structural features were determined by single crystal X-ray diffraction analyses. The results showed that the complexes 1, 2 and 3 have homologous mono-nuclear structures, in which the five-coordinated Cu(II) atom is not only surrounded by the N3O cavity of the ligand (L)(-) unit, but also coordinated with Cl-, Br- and NO3- as auxiliary coordination, respectively. The ligand HL and the complexes 1, 2 and 3 were characterized via elemental analyses, IR and UV-Vis spectroscopy. The short-range interactions of the complexes 1, 2 and 3 were investigated by Hirshfeld surfaces analyses. Furthermore, DFT calculations were investigated in the complexes 1, 2 and 3. Paradoxically, the fluorescence intensities of these Cu(II) complexes are significantly increased compared to the ligand.

Automated summary

A new pyridine-decorated half-salamo-like ligand (HL) was successfully designed and synthesized, leading to the cultivation of three anion-dependent Cu(II) complexes. The structural features of the complexes were determined by various analyses, revealing homologous mono-nuclear structures with unique coordination characteristics. Additionally, the fluorescence intensities of these Cu(II) complexes were found to be significantly increased compared to the ligand.