Synthesis, characterization and spectroscopic properties of 1,2-diiminetricarbonylrhenium(I)chloride complexes with o-benzoquinone diimines as ligands

The novel organometallic complexes Re(BQDIR)(CO)3Cl with BQDIR=4,5-substituted o-benzoquinone diimines (R=H, Me, OMe, Cl) have been prepared and characterized by elemental analysis, IR, MS and 1H-NMR spectroscopic methods. Their electronic spectra display a long-wavelength absorption band which can be ascribed to a metal-to-ligand charge transfer (MLCT) transition from Re(I) to the low-lying π*-orbitals of the o-benzoquinone diimine ligand, even though a significant degree of metal–ligand orbital mixing is occurring. The energy of this absorption band correlates very well with the nature of the substituents R in the 4,5-position of BQDIR. In solvent series of decreasing polarity, the MLCT absorption maximum is shifted to longer wavelengths (negative solvatochromism). None of the Re(BQDIR)(CO)3Cl complexes studied is photoluminescent at 298 or 77 K.