Cobalt(II)–dibenzotetraaza[14]annulene complex electropolymerization for electrode modification

Solution and Solid State Properties for Low-Spin Cobalt(II) Dibenzotetramethyltetraaza[14]annulene [(tmtaa)CoII] and the Monopyridine Complex

The single-crystal X-ray structure of solvent-free (tmtaa)Co^II reveals three different π-π intermacrocyclic interactions between tmtaa units (tmtaa = dibenzotetramethyltetraaza[14]annulene). Pairs of inequivalent (tmtaa)Co^II units in the unit cell link into a one-dimensional π-π stacked array in the solid state. Magnetic susceptibility (χ) studies from 300 to 2 K reveal the effects of intermolecular interactions between (tmtaa)Co^II units in the solid state. The effective magnetic moment per Co^II center is constant at 2.83 μ_B from 300 to 100 K and begins to significantly decrease at lower temperatures. The magnetic data are fit to a singlet ( S = 0) ground state with a triplet ( S = 1) excited state that is 13 cm^-1 higher in energy (-2 J = 13 cm^-1). Toluene solutions of (tmtaa)Co^II have ¹H nuclear magnetic resonance (NMR) paramagnetic shifts, a solution-phase magnetic moment μ_eff (295 K) of 2.1 μ_B, and toluene glass electron paramagnetic resonance spectra that are most consistent with a low-spin ( S = ¹/₂) Co^II with the unpaired electron located in the d _yz orbital. Pyridine interacts with (tmtaa)Co^II to form a five-coordinate monopyridine complex in which the unpaired electron is in the d _z² orbital. The five-coordinate complex has been structurally characterized by single-crystal X-ray diffraction, and the equilibrium constant for pyridine binding at 295 K has been evaluated by both electronic and ¹H NMR spectra. Density functional theory computation using the UB3LYP hybrid functional places the unpaired electron for (tmtaa)Co^II in the d _yz orbital and that for the monopyridine complex in the d _z² orbital, consistent with spectroscopic observations.

A molecular material based on electropolymerized cobalt macrocycles for electrocatalytic hydrogen evolution

Electropolymerization of CoTAA gives an electrocatalytic material for the H₂ evolution reaction in acidic aqueous solution.

Recent advances in the electrochemistry of porphyrins and phthalocyanines

Recent developments in the electrochemistry of metalloporphyrins and metallophthalocyanines are reviewed briefly by focusing on the electroanalytical, electrocatalytic and electrochemical sensor applications.