Cu(i) complexes of dihydrobis(2-mercapto-benzimidazolyl)borate and dihydrobis(2-mercapto-benzothiazolyl)borate ligands: structural, photophysical and computational studies

Abstract

The salt metathesis reaction of CuI with two sodium precursors (NaBb and NaBb-1) of bipodal scorpionate type ligands [Bb = dihydrobis(2-mercapto-benzimidazolyl)borate, (Bb-1 = dihydrobis(2-mercapto-benzothiazolyl)borate)] has been explored in the presence of selected phosphine ligands (PPh₃, PCy₃, PPh₂Me, PPh₂Py). All of the resulting Cu(I) complexes were formed as predominantly a single monomeric isomer and were characterized using a combination of ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, and in two cases by X-ray crystallography. In the X-ray crystal structure of complexes 1 and 6, the Cu(I) center adopts a distorted tetrahedral geometry. Complexes 1 and 6 exhibit (B)H⋯Cu distances of 2.008 Å and 1.866 Å length, respectively. Based on IR spectroscopy and X-ray crystallography data, 1 and 6 adopt a κ³-S,S,H coordination mode in the solid state. All the metal complexes were screened for their photoluminescence properties in the solid state at different temperatures (298 K and 77 K). These complexes feature emission bands at room temperature in the range 527–571 nm, among which complex 3 and complex 6 reveal stronger thermochromic behavior at lower temperature. The data from the X-ray crystallography studies for 1 and 6 were used to optimize their structures computationally. Density Functional Theory (DFT) analyses were also conducted on the optimized structures to learn about the sources of electronic transitions in these complexes.