Synthesis, crystal structure, properties, and theoretical studies of novel tetra-nuclear copper(II) salamo-like complex containing four- and five-coordinated geometries

A novel tetra-nuclear Cu(II) salamo-like complex containing four- and five-coordinated Cu(II) atoms, [Cu4(L)2(MeOH)2]& BULL;2MeOH was synthesized and characterized structurally. The single crystal X-ray diffraction analysis indicated the Cu(II) complex is a triclinic system, including four Cu(II) atoms and two completely deprotonated ligand (L)4- units, forming an asymmetric geometric structure. Specifically, Cu2 and Cu4 atoms are located in the N2O2 cavities of two different ligand (L)4- units, respectively, and coordinate with one methanol molecule in the axial position to form five-coordinated tetragonal pyramid geometries. Meanwhile, Cu1 and Cu3 atoms respectively coordinate with four phenoxy atoms in the two ligand (L)4- units to form slightly distorted planar quadrilateral geometries with four coordination. The spectral properties of the ligand H4L and its Cu(II) complex were further analyzed by IR, UV-vis absorption spectra and fluorescence spectra. DFT calculation results showed that the Cu(II) complex has low optical reaction activity. In addition, the electrophilic and nucleophilic sites favorable for the formation of hydrogen bonds were found through molecular electrostatic potential analysis. Hirshfeld surface analysis identified the interactions in the crystal structure. In the Cu(II) complex, H & BULL;& BULL;& BULL;H/H & BULL;& BULL;& BULL;H interaction is dominant, indicating that there are a large number of hydrogen bonds in the complex. IRI analysis revealed that there are weak hydrogen bond interactions, all of which make the Cu(II) complex more stable.