The Role of Redox Potential and Molecular Structure of Co(II)-Polypyridine Complexes on the Molecular Catalysis of CO2 Reduction

In this work, we report the electrochemical response of a family of Co(II) complexes, [CoII(L)3]2+ and [CoII(L’)2]2+ (L = 2,2’-bipyridine, 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline; L’ = terpyridine and 4-chloro-terpyridine), in the presence and absence of CO2 in order to understand the role of the redox potential and molecular structure on the molecular catalysis of CO2 reduction. The tris chelate complexes exhibited three electron transfer processes [CoII(L)3]2+ ⇄ [CoIII(L)3]3+ + 1e−, [CoΙΙ(L)3]2++1e− ⇄ [CoΙ(L)3]+, and [CoΙ(L)3]+ + 2e- ⇄ [CoΙ(L)(L−)2]−. In the case of complexes with 1,10-phen and 2,2-bipy, the third redox process showed a coupled chemical reaction [CoΙ(L)(L−)2]− → [CoΙ(L−)2]− + L. For bis chelate complexes, three electron transfer processes associated with the redox couples [CoΙΙ(L)2]/[CoIII(L)2]3+, [CoΙΙ(L)2]2+/[CoΙ(L)2]+, and [CoΙ(L)2]+/[CoΙ(L)(L−)] were registered, including a coupled chemical reaction only for the complex containing the ligand 4-chloro-terpyridine. Foot to the wave analysis (FOWA) obtained from cyclic voltammetry experiments allowed us to calculate the catalytic rate constant (k) for the molecular catalysis of CO2 reduction. The complex [Co(3,4,7,8-tm-1,10-phen)3]2+ presented a high k value; moreover, the complex [Co(4-Cl-terpy)3]2+ did not show catalytic activity, indicating that the more negative redox potential and the absence of the coupled chemical reaction increased the molecular catalysis. Density functional theory (DFT) calculations for compounds and CO2 were obtained to rationalize the effect of electronic structure on the catalytic rate constant (k) of CO2 reduction.

Redox Behavior of Chelate Complexes Based on 8-Oxyquinoline Promising in OLED Display Technology

The electrochemical behavior of 8-oxyquinoline and chelate complexes based on it (Sn (Oxin)Cl3, Ge (Oxin)Cl3, Ti (Oxin)Cl3, W(Oxin)2Cl4, Fe (Oxin)Br, Sb (Oxin)Cl2, Sb (Oxin)Cl4, Sn (Oxin)2Cl2, Ti (Oxin)2Cl2 have been studied by cyclic voltammetry in aprotic solvents in a three-electrode system on platinum and glass-graphite disk electrodes. It has been shown that in the case of metal oxyquinolinates, the ligand is 8-oxyquinoline reducing in two one-electron diffusion waves. The first wave is observed at less negative potentials than the first quinoline one, while the second waves have almost the same potentials. The first wave is related to the OH- proton discharge. The complexes under study are electrolytically oxidizable. A single two-electron peak is observed in the cyclic voltammogram in the anodic region for the Ti (Oxin)Cl3 chelate complex. This is probably associated with two irreversible sequential or parallel stages with close oxidation potentials. By analogy to the processes considered for 8-oxyquinoline, the rupture of the oxygen-metal bond is observed at the first stage. The resulting radical cation is unstable and decomposes into a radical and a cation with a positive charge in the titanium atom. Electrolytic oxidation of complexes Fe (Oxin)Br, Sb (Oxin)Cl2, Sb (Oxin)Cl4, and Sn (Oxin)2Cl2 is similar to that of Ti (Oxin)Cl3.

NITROGEN-CONTAINING CHELATE COMPLEXES AND MONOMERS BASED ON THEM

By the interaction between N-methylolthiourea and Co2+, Mn2+ acetates are obtained compounds that were later used for the synthesis of vinyl bifunctional groups containing polymerizable chelate complexes. These compounds are recommended to be used as crosslinkers for obtaining, on the basis of water-based soluble monomers, spatially cross-linked water-swellable copolymers with applied purpose. There are dynamics of water absorption of copolymers from the time of their stay in water.

JUSTIFICATION OF THE APPLICATION OF MICROELEMENT ADDITIVES WHEN DEVELOPING MULTI-COMPONENT MELIORANTS FOR USE ON GRAY FOREST SOILS RYAZAN REGION

The specificity of the soil formation conditions of the gray forest soils of the Ryazan region predetermined the low content of some microelements (for example, cobalt and molybdenum) in them, which take an active part in metabolism and enzymatic reactions. Their shortage leads not only to a decrease in the yield, but also to a sharp deterioration in its quality. In case of their deficiency in the basic components of complex ameliorants, it is recommended to provide for their additional introduction into the fertilizer in the form of chelate complexes.

Cymantrene Derivatives Containing Imino Groups: Spectral and Photochemical Properties

The investigation of a photochemical behavior of imino derivatives of cymantrene reveals a possibility of formation of four-membered hemilabile chelate complexes. In the presence of external ligands, such as CO, MeCN, or PPh3, the ligand exchange between imino groups at the Mn atom in dicarbolyl chelates and the external ligand is observed. It is shown that MeCN or PPh3 can be substituted for CO under dark conditions, resulting in intermolecular photochromic systems between tricarbonyl complexes and dicarbonyl derivatives with MeCN and PPh3 ligand, respectively.

Foreword from the Editor of Special Issue “Advanced Metal Chelate Complexes: Quantum-Chemical Consideration”

The objects of the given Special Issue of Materials—coordination compounds or complexes, represent a kind of “boundary zone” between two main classes of chemical substances, inorganic and organic, and therefore differ in a significantly greater variety of their structural and physicochemical characteristics in comparison with both inorganic and organic compounds [...]