Novel trans-dioxorhenium complex with imidazo[1,2a]pyridine ligand – Synthesis, spectroscopic and electrochemical characterization, X-ray crystal structure and DFT calculations

The reaction of [ReO2(py)4]Cl with imidazo[1,2a]pyridine has been examined and a novel dioxorhenium(V) complex – [ReO2(impy)4]Cl·MeCN·2H2O with trans-[OReO]+ core has been obtained. The X-ray crystal structure of the complex has been determined and the electronic structure has been examined using the density functional theory (DFT) method. The UV–Vis absorption spectrum of the complex has been interpreted on the basis of the results of time-dependent DFT (TDDFT) calculations. Electrochemical reaction of [ReO2(impy)4]+ in CH3CN solution containing tetra-n-butylammonium perchlorate as a supporting electrolyte has been studied using cyclic voltammetry at 25 °C. Cyclic voltammograms show one redox couple around 0.156 (Epa) and 0.080 V (Epc) [versus ferrocene/ferricenium ion redox couple, (Fc/Fc+)]. Potential differences between two peaks (ΔEp) at scan rates (v) in the range from 0.04 to 0.20 V s−1 are ca. 75 mV, which is almost consistent with the theoretical ΔEp value (59 mV) for the reversible one electron transfer reaction at 25 °C. The ratios of anodic peak currents to cathodic ones are in the range from 4.76 (v = 0.04 V s−1) to 3.11 (v = 0.20 V s−1) and the (Epa + Epc)/2 value is constant, 0.118 ± 0.001 V versus Fc/Fc+, regardless of the scan rate. Spectroelectrochemical experiments have also been carried out by applying potentials from 0.009 to 0.159 V versus Fc/Fc+ with an optically transparent thin layer electrode. It was found that the UV–Vis absorption spectra show clear isosbestic points at 218.9, 248.3 and 292.8 nm, and that the electron stoichiometry is evaluated as 1.04 from the Nernstian plot. These results indicate that the [ReO2(impy)4]+ complex is oxidized quasi-reversibly to the [ReO2(impy)4]2+ complex.

A novel dioxorhenium(V) complex incorporating imidazo[1,2a]pyridine has been synthesized and characterized by spectroscopic and electrochemical methods and its crystal structure was determined by single-crystal X-ray diffraction analysis. The complex shows a trans-dioxo geometry and its equatorial plane is occupied by four impy molecules in a paddle-wheel-arrangement. The electronic spectrum was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ. The electrochemical and spectroelectrochemical studies showed that [ReO2(impy)4]+ is quasi-reversibly oxidized to [ReO2(impy)4]2+.Figure optionsDownload as PowerPoint slideHighlights
► A novel Re(V) dioxocomplex of imidazo[1,2a]pyridine was synthesized.
► The compound was investigated by spectroscopic methods and X-ray analysis.
► Electrochemical reaction of [ReO2(impy)4]+ was studied using cyclic voltammetry.
► The electronic structure and spectroscopic features of [ReO2(impy)4]+ were investigated by DFT method.