Syntheses And Quantum Calculations Of1,2-naphthoquinone-1-oxime Rhodium (â…¢)Complexes Containing Chloride Ligands

1,2-Naphthoquinone-mono-oximes are electron donor ligands with π-accepting ability. Metal complexes containing1,2-naphthoquinone-monooximes are of interest as they are widely used for analytical purposes and are potentially useful for the preparation of a wide variety of organic compounds. Rhodium (Ⅲ) complexes of1,2-naphthoquinone-l-oxime (1-nqo) containing chloride ligands were synthesized through a reaction of rhodium chloride with1,2-naphthoquinone-l-oxime and pyridyl co-ligand (pyridine,4-methylpyridine,4-phenylpyridine,4-acetylpyridine). The products were purified through thin layer chromatography. Eight products were obtained as Rhodium (Ⅲ) complexes of1,2-naphthoquinone-l-oxime containing chloride ligands. The structures of the products were analyzed by single crystal X-ray diffraction, FAB MS,1H NMR, IR and UV. Theoretical calculations for rhodium complexes were performed by Gaussian software package suite. The structures and UV-vis spectra of the products were analyzed by density functional theory (DFT) and time-dependent density functional theory (TD-DFT).Rhodium(Ⅲ) complexes of1,2-naphthoquinone-l-oxime [Rh(1-nqo)(py)2Cl2]1, cis, trans-[Rh(1-nqo)2(py)Cl](cis-NO, trans-O)2and cis, cis-[Rh(1-nqo)2(py)Cl](cis-NO, cis-O)3were prepared by a controlled reaction. The structures of complex1and2were analyzed by single crystal X-ray crystallography. All complexes were characterized by mass spectrometry and1H NMR. Spin unrestricted DFT wavefunction was used for geometry optimization. Good results were obtained by the calculation using "double-ξ" quality basis set LanL2DZ and effective core potential for Rh atom and6-31G (d, p) basis set for C, H, N, O and Cl atoms. The vertical excitation energies to the singlet excited states of the complexes were calculated at TD-B3LYP theoretical level. The properties of the products were analyzed in detail by orbital, molecular orbital and UV spectrum. The structure of complex3was predicted. Rhodium(III) complexes of1,2-naphthoquinone-l-oxime (1-nqo)[Rh(1-nqo)L2Cl2]4-6[4, L=4-methylpyridine (mpy);5, L=4-phenylpyridine (ppy);6, L=4-acetylpyridine (apy)] were prepared and calculated by DFT and TD-DFT. Geometry optimizations were conducted for complexes4-6. The optimized stationary points of complexes were confirmed to be local minima as no imaginary vibrational frequencies appear. Based on the optimized geometries, the vertical excitation energies of both the singlet and triplet excited states of the complexes were calculated at TD-B3LYP theoretical level. UV-vis absorption spectroscopy and cyclic voltammetry were employed to investigate the electronic transition behaviors of the complexes. The complexes display irreversible two-electron metal-localized reduction from RhⅢ to RhⅠ on the cyclic voltammogram.Rhodium(Ⅲ) complexes of1,2-naphthoquinone-1-oxime (1-nqo)[Rh(1-nqo)2(ppy)Cl]7and [Rh(1-nqo)2(apy)Cl]8were prepared and purified. Theoretical calculations were conducted on six isomers for each of the complexes7-8by DFT and TD-DFT, respectively. The band lengthes, band angles, frontier orbital, IR and UV spectra of all the isomers were calculated. The probable structure of complex7and8were predicted based on calculation results to be cis,cis-[Rh(1-nqo)2(ppy)Cl] and cis,cis-[Rh(1-nqo)2(apy)Cl] with the two oxime groups, as well as the two naphthoquinonic O group in the two1-nqo cis to each other, while the pyridly ligand trans to naphthoquinonic O group in one of the1-nqo and the chloride trans to the oxime group in another1-nqo.