Most non-metalized Salen-type ligands form passivation thin films on electrode surfaces upon electrochemical oxidation. In contrast, the H₂(3-MeOSalen) forms electroactive polymer films similarly to the corresponding nickel complex. There are no details of electrochemistry, doping mechanism and charge transfer pathways in the polymers of pristine Salen-type ligands. We studied a previously uncharacterized electrochemically active polymer of a Salen-type ligand H₂(3-MeOSalen) by a combination of cyclic voltammetry, in situ ultraviolet–visible (UV–VIS) spectroelectrochemistry, in situ electrochemical quartz crystal microbalance and Fourier Transform infrared spectroscopy (FTIR) spectroscopy. By directly comparing it with the polymer of a Salen-type nickel complex poly-Ni(3-MeOSalen) we elucidate the effect of the central metal atom on the structure and charge transport properties of the electrochemically doped polymer films. We have shown that the mechanism of charge transfer in the polymeric ligand poly-H₂(3-MeOSalen) are markedly different from the corresponding polymeric nickel complex. Due to deviation from planarity of N₂O₂ sphere for the ligand H₂(3-MeOSalen), the main pathway of electron transfer in the polymer film poly-H₂(3-MeOSalen) is between π-stacked structures (the π-electronic systems of phenyl rings are packed face-to-face) and C-C bonded phenyl rings. The main way of electron transfer in the polymer film poly-Ni(3-MeOSalen) is along the polymer chain, while redox processes are ligand-based.

Conductive and electrochemically active polymers consisting of Salen-type metal complexes as building blocks are of interest for energy storage and conversion applications. Asymmetric monomer design is a powerful tool for fine-tuning the practical properties of conductive electrochemically active polymers but has never been employed for polymers of M(Salen)]. In this work, we synthesize a series of novel conducting polymers composed of a nonsymmetrical electropolymerizable copper Salen-type complex (Cu(3-MeOSal–Sal)en). We show that asymmetrical monomer design provides easy control of the coupling site via polymerization potential control. With in-situ electrochemical methods such as UV-vis-NIR (ultraviolet-visible-near infrared) spectroscopy, EQCM (electrochemical quartz crystal microbalance), and electrochemical conductivity measurements, we elucidate how the properties of these polymers are defined by chain length, order, and cross-linking. We found that the highest conductivity in the series has a polymer with the shortest chain length, which emphasizes the importance of intermolecular iterations in polymers of [M(Salen)].

Crystal structures of N,N'-ethylenebis(3-nitrosalicylideneiminato)nickel(II) [Ni(3-NO₂SalEn)] and N,N'-(2,3-dimethylbutane-2,3-diyl)bis(3-nitrosalicylideneiminato)nickel(II) [Ni(3-NO₂SaltmEn)] were determined by single crystal X-ray diffraction analysis. The [Ni(3-NO₂SalEn)] complex forms supramolecular associates in the crystal phase, which affects its solubility, thermogravimetric, and spectral characteristics.