Spectroscopic, structural, electrochemical and computational studies of some new 2-thienyl-containing β-diketonate complexes of cobalt(II), nickel(II) and copper(II)

In this work, we present the synthesis of the unsymmetrical β-diketone 1-(2-thienyl)-3-(4-fluorophenyl)-propane-1,3-dione (HL) and its corresponding Co(II), Ni(II) and Cu(II) bis(β-diketonato) complexes 1–3, respectively. The four new compounds were isolated in good yields (65–70%), and characterized by mass spectrometry, elemental analysis, FT-IR and UV–Vis spectroscopy and, in the case of HL, by ¹H, ¹³C and ¹⁹F NMR spectroscopy. In addition, the molecular identities and the geometries of the β-diketone HL and complex 3 were confirmed by X-ray diffraction analysis. The dicarbonyl derivative HL does exist as the diketo tautomeric form in DMSO solution and as its keto-enol tautomer in the solid-state with the –OH group adjacent to the 4-fluorophenyl unit. The keto-enol isomer was computed to be more stable by 8.2 kcal/mol in free energy at room temperature. In 3, the Cu(II) center adopts a perfect square-planar geometry. Two reduction processes were observed in the cyclovoltammogram of 3 at −1.30 and −1.80 V vs. Fc/Fc⁺, with copper deposit on the surface of the electrode. DFT and TD-DFT calculations on HL and complex 3 allow rationalizing their stability, bonding and properties.