M.F. El-Shahat

Spectroscopic and electrochemical activity studies of some molybdenum chrysenesemiquinone complexes

Abstract Five molybdenum complexes were isolated from the reactions of chrysenequinone and Mo(CO) 6 . All the isolated complexes were found to be dimeric and contained MoO bonds. The IR spectra of these complexes showed strong ν(CO) bands due to semiquinone type bonding. The vibrational spectrum of Mo 2 O 2 (CO) 4 (ChrySQ) 2 (ChrySQ = chrysenesemiquinone) also showed ν(CO) bonds due to terminal and bridged CO groups. Two complexes with stoichiometry of Mo 2 O 4 (CO) 2 (ChrySQ) 2 were found to be isomeric in cis and trans forms. The electronic absorption spectra of Mo 2 O 4 (CO) 2 (ChrySQ) 2 and Mo 2 O 2 (CO) 4 (ChrySQ) 2 in DMSO displayed bands due to the formation of molybdenum compound-solvent charge transfer complexes. The energies of the charge transfer complexes ( E CT ) were calculated either theoretically from the ionization potential of the donor and the electron affinity of the acceptor, or experimentally from the UV-vis spectra of the complexes. Examination of Mo 2 O 4 (CO) 2 (ChrySQ) 2 by cyclic voltammetry showed two quasi-reversible redox reactions due to tautomeric interconversions of the semiquinone-catechol couples through electron transfer.

Synthesis and characterization of cis- and trans-bis (chrysenesemiquinonemonoxime) dicarbonyltetraoxodimolybdenum (V) complexes

Abstract Reaction of Mo(CO) 6 with chrysenequinonemonoxime, ChryQM, gave two complexes with the stoichiometry Mo 2 O 4 (CO) 2 (ChrySQM) 2 . These compounds were found to exist in cis and trans isomeric forms. From their IR spectra, it was concluded that the ligands are bonded to the metal in the semiquinone form. The vibrational spectra also showed ν (CO) bands in the metal carbonyl region due to terminal CO groups. The UV—vis spectra of the two complexes showed strong UV bands due to metal-to-ligand charge transfer. Also, in DMSO the spectra displayed bands due to the formation of molybdenum compound-solvent charge-transfer complexes. The energies of the CT complexes ( E CT ) were calculated either theoretically or experimentally from the UV—vis spectra. Investigation of Mo 2 O 4 (CO) 2 (ChrySQM) 2 by cyclic voltammetry showed two anodic waves with no coupled cathodic waves on the reverse scan (irreversible process).

The synthesis, spectral and magnetic properties of the complexes of chromium with chrysenequinone and chrysenequinonemonoxime☆

Abstract Reactions of the chromium hexacarbonyl with chrysenequinone and chrysenequinonemonoxime gave the tris(chrysenesemiquinone)chronium(III), Cr(ChrySQ) 3 , and tris(chrysenesemiquinonemonoxime)chromium(III), Cr(ChrySQM) 3 , complexes. From the stretching frequencies of the carbonyl groups in the IR spectra of the complexes, it was concluded that the ligands bonded to the metal in the semiquinone form. Also, the electronic absorption spectra of the two complexes showed strong UV bands due to metal-to-ligand charge transfer. The magnetic susceptibility determination for the Cr(ChrySQ) 3 complex at 300 K gave a value of 3.261 × 10 −6 e.m.u.g −1 with an effective magnetic moment (μ eff ) of 2.55 μ B . Investigation of Cr(ChrySQ) 3 and Cr(ChrySQM) 3 by EPR spectroscopy at room temperature showed isotropic g values of 1.997 and 1.991 for the two complexes, respectively. The isotropic g values are greater than those observed previously for various o semiquinone chromium complexes. Chrysenequinonemonoxime reacted with Cr(NO 3 ) 3 to give the bis(chrysenequinonemonoximato) (chrysenequinonemonoxime)chromium(III)nitrate. Spectroscopic studies of the complex suggested that the chrysenequinonemonoxime ligand is attached to the metal in both nitroso and oxime forms. Examination of the chromium complexes by cyclic voltammetry showed some reversible or quasireversible redox reactions due to tautomeric interconversions of the semiquinone—catechol couples through electron transfer.