Syntheses and characterization of five-coordinate copper(II) complexes based on tridentate SNS pincer ligand precursors

Abstract A series of tridentate pincer ligands, each possessing two sulfur- and one nitrogen-donor functionalities (SNS), based on a bis-imidazolyl precursor were metallated with CuCl 2 to give new tridentate SNS pincer copper(II) complexes [(SNS)CuCl 2 ]. These purple complexes exhibit a five-coordinate pseudo-square pyramidal geometry at the copper center. The [(SNS)CuCl 2 ] complexes were characterized with single crystal X-ray diffraction, electrospray mass spectrometry, EPR spectroscopy, attenuated total reflectance infrared spectroscopy, UV–Vis spectroscopy, cyclic voltammetry, and elemental analysis. The EPR spectra are consistent with typical anisotropic Cu(II) signals with four hyperfine splittings in the lower-field region ( g || ). Various electronic transitions are apparent in the UV–Vis spectra of the complexes and originate from d-to-d transitions or various charge transfer transitions. We preformed computational studies to understand the influence that structural constraints internal to our tridentate SNS ligand precursors have on the oxidation state of the resulting bound copper complex. We have determined that a d 9 copper(II) metal center is better situated than a d 10 copper(I) center to bind our tridentate SNS ligand set when it does not contain an internal CH 2 group. Without this methylene linker, the SNS ligand forces the N and S atoms into a T-shaped arrangement about the metal center.