Octahedral bis(2-thenoyltrifluoroacetonato)-ethylenediamine Co(II), Ni(II) and Cu(II) complexes: Synthetic, structural, electrochemical, and theoretical studies

Abstract : We report the synthesis of three new octahedral bis(2-thenoyltrifluoroacetonato)-ethylenediamine metal(II) complexes [M(TTA)2(en)] (M = Co, 2a; Ni, 2b; Cu, 2c) resulting from the coordination of the diamine onto the bis(β-diketonate) precursors [Co(TTA)2(CH3OH)2] (1a), [Ni(TTA)2(H2O)2] (1b) and [Cu(TTA)2] (1c), respectively. The six-coordinate paramagnetic complexes 2a-c have been isolated as neutral, air and thermally stable solids in high yields (andgt;80%) and have been fully characterized by elemental analysis, ESI+ HRMS, FT-IR and UV–vis spectroscopy. Single-crystal X-ray diffraction studies indicate that the metal(II) ion sits in a pseudo-octahedral environment; the copper derivative 2c showing a significant elongation along the O–Cu–O axis due to Jahn-Teller distorsion associated with the “eg” electron occupation of the dz2-type MO. The three complexes 2a-c display similar cyclic voltammetric behavior exhibiting two irreversible anodic waves, tentatively assigned to the M(II)/M(III) redox couples and to the oxidation of soluble short oligomeric species generated during the first redox process, respectively. No deposits of polymeric species on the electrode surface occured. The electronic structures of 2a-c and their cations have been analysed through DFT calculations, allowing providing a consistent view of their structure and properties. TDDFT calculations have been used to interpret the major features of their UV–vis spectra. © 2017 Elsevier B.V.