Syntheses, characterizations and theoretical calculations of rhodium(III) 1,2-naphthoquinone-1-oxime complexes

Rhodium(III) complexes of 1,2-naphthoquinone-1-oxime (1-nqo) [Rh(1-nqo)L2Cl2] 1–3 [1, L = 4-methylpyridine (mpy); 2, L = 4-phenylpyridine (ppy); 3, L = 4-acetylpyridine (apy)] were prepared. The structure of complex 1 is analyzed by single crystal X-ray crystallography. All of the complexes were characterized by mass spectrometry, 1H–1H COSY NMR and FT-IR. UV–Vis absorption spectroscopy and cyclic voltammetry were employed to investigate the electronic transition behaviors of the complexes. The complexes displayed irreversible metal-localized two-electron reductions from RhIII to RhI on the cyclic voltammogram. While the low-energy absorptions at λmax of 488–490 nm on the UV–Vis spectra of the complexes were related to metal to 1-nqo ligand charge transfer [MLCT, dπ(Rh) → π∗(1-nqo)] and chloride to 1-nqo ligand charge transfer [LLCT, pπ(Cl) → π∗(1-nqo)] based on the theoretical calculations using time-dependent density functional theory (TD-DFT).