cis- and trans-Bis(pyridine)chromium(III) complexes containing mixed-valence chrysenesemiquinonate-chrysenecatecholate ligands: Synthesis, characterization and interpretation of the electronic absorption spectra using ZINDO/S method

Two new geometrical isomers of [Cr(py)2(chrySQ)(chryCat)] were synthesized by two different synthetic procedures. The structures of the two isomers have been modeled using parameterized PM3 semiempirical method. Theoretical harmonic vibrational frequencies of the cis- and trans-isomers have been computed and compared well with the experimental vibrational frequencies. Theoretical modeling of the magnetic data indicated strong antiferromagnetic exchange interaction between CrIII (S = 3/2) and chrySQ (S = 1/2) with J = −365 ± 6 and −395 ± 4 cm−1 for the cis- and trans-isomers, respectively. The electrochemical behavior of cis- and trans-[Cr(py)2(chrySQ)(chryCat)] complexes were studied by cyclic voltammetry in acetonitrile solvent. The electronic spectra of the two isomers were dominated by charge-transfer (LMCT, MLCT and ILCT) transitions. In addition, a low-energy intervalence charge-transfer (IVCT) transition was observed for the cis-isomer at 1085 nm. Theoretical studies of the electronic spectra by ZINDO/S-CI method were useful in interpreting the observed electronic transitions.