Cu(II) complexes with square pyramidal (N2S)CuCl2 chromophore: Jahn–Teller distortion and subsequent effect on spectral and structural properties

One monomeric neutral Cu(II) complex [(pmtpm)CuCl2] (1) is reported by Lindoy and Livingstone [8]. Two new complexes namely, μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu(Cl)}2 μ-Cl](ClO4) (2) and a bis μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu}2(μ-Cl)2](ClO4)2 (3) derived from a tridentate Schiff base ligand, 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (pmtpm) were synthesized and characterized by various spectroscopic methods and by X-ray crystallography. (N2S)CuCl2 chromophore(s) of distorted square pyramidal coordination geometries around Cu(II) ion(s) have been observed for all the complexes 1–3. The equatorial sites of the square plane comprise two N and a thioether S donor atoms of the pmtpm ligand as well as one Cl− ion (terminal in 1 and 2, and bridging in 3) while the remaining axial site is occupied by a terminal Cl− ion (for 1) or a bridging Cl− ion (for 2 and 3). The equatorial Cu–Cl distances are much shorter [1: 2.2511(4) Å, 2: 2.2307(12) Å, 3: 2.2513(12) Å] than the axial Cu–Cl distances [1: 2.4394(4) Å, 2: 2.5597(9) Å, 3: 2.7037(12) Å]. The correlation of an axial Cu–Cl bond elongation with a lower g|| value in the solid state EPR spectrum and a blue shifted ligand field transition in the solid and solution phase absorption spectrum has been observed.

Graphical abstractTwo new binuclear Cu(II) complexes (monochloro and dichloro bridged) derived from a tridentate Schiff base ligand, 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (pmtpm) were synthesized and characterized by various spectroscopic methods including X-ray structures. (N2S)CuCl2 chromophore(s) of distorted square pyramidal coordination geometry around Cu(II) ions have been observed for these complexes. The trend of axial Cu–Cl bond elongation due to Jahn–Teller effect is associated with a lower g|| value in the solid state EPR spectrum and a blue shifted ligand field transition in the solid and solution phase absorption spectrum has been observed.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► N,S donor tridentate supporting ligand. ► Dicopper(II) complexes with N2SCl2 coordination zone around Cu(II). ► Pseudo Jahn-Teller distortion in square pyramidal Cu(II) complexes. ► Solid and solution phase absorption spectra and EPR spectra. ► Cyclic voltammograms (redox chemistry).