Recently, scientists from St. Petersburg State University, in collaboration with colleagues, conducted research focusing on the structural changes that occur when organometallic complexes are converted into conductive polymers. The related results were published in the scientific journal Physical Chemistry Chemical Physics.
Organometallic complexes [Ni(Salen)] are typical representatives of transition metal complexes with Salen-type Schiff base ligands. Their functional derivatives (polymers) possess unique properties such as high conductivity, thermal stability, electrochromism, and selective heterogeneous catalytic activity, making them suitable for applications in electronic devices, sensors, energy storage devices, and catalysis. Over the past 20 years, the polymerization mechanism of [Ni(Salen)] has been a hot topic. This study identified the key structural units that determine the properties of the initial [Ni(Salen)] complex and the resulting polymer, helping to better understand its polymerization mechanism and highlighting its important contribution to the development of modern chemistry.
Petr Korusenko, Senior Researcher at the Department of Solid State Chemistry at St. Petersburg University, explained that the study is the first to investigate in detail the structural changes of the [NiO₂N₂] coordination center when transitioning from the [Ni(Salen)] complex to its polymer, as well as the structural units that determine the key properties of the system. During electrochemical oxidation, the [NiO₂N₂] coordination center of the [Ni(Salen)] molecule becomes distorted due to changes in the electronic structure of the Salen ligand atoms. When the system returns to a neutral state, the structure almost completely reverts to its original square-planar geometry, which allows for a better understanding of the details of the complex's polymerization process.
The scientists also discovered that in the condensed phase, [Ni(Salen)] complexes consist of dd-stacked dimers. In the polymer poly[Ni(Salen)], these "building blocks" are connected via carbon atoms of the phenolic fragments (C₆H₅O) into tetramers, forming an extended three-dimensional network. In addition, it was confirmed that electrolyte counterions adsorbed during the electrochemical polymerization of [Ni(Salen)] affect the charge state of the nickel atom in the coordination center—an effect not previously described in the literature.
Previously, scientists from the same research group developed a method to bond multi-walled carbon nanotubes to titanium substrates without using polymer binders, which can be used to develop new composite electrode materials for high-performance supercapacitors. The team's upcoming plans include studying the characteristics of [Ni(Salen)] polymerization on carbon nanotubes to create efficient electrode materials for batteries and supercapacitors.
