Thermochemistry of a Cobalt Complex with Ionisable Pyrazole Protons

Abstract

Herein, we present the thermodynamic analysis of a cobalt complex with a new pentadentate N-donor ligand bearing four ionisable pyrazole protons in aqueous solution. A detailed analysis of the Co II complex [Co(L)(X)] +/2+ in the solid state revealed that the 6 th ligand X at the metal centre depends on the cobalt source employed. Small anions such as Cland NO 3 coordinate to the metal ion, while larger anions that are weaker hydrogen-bond acceptors are found in the second coordination sphere of the complex and instead a solvent molecule coordinates. However, in aqueous KCl solution, the sixth ligand [a]

Imidazole for Pyridine Substitution Leads to Enhanced Activity Under Milder Conditions in Cobalt Water Oxidation Electrocatalysis

“…The crystal structure of complex 3 (Figure ) confirms the assignment of the complex as a mononuclear acetonitrile adduct with outer sphere triflate counter-anions. Bond distances between Co and the imidazolyl/pyridyl donors for complex 3 average 2.09 Å, which is similar to those of the previously reported tetraimidazolylpyridine system (2.10 Å, complex 2 ) but somewhat shorter than the analogous pentapyridine Co complex (2.16 Å, complex 1 ), as might be expected due to differences in the donating abilities of the pyridyl and imidazolyl ligands. , Complex 3 shows characteristically shifted paramagnetic peaks in its 1 H NMR spectrum, consistent with a C 2 v -symmetric complex in solution (see SI). Furthermore, EPR spectroscopy indicates that the Co II center is high spin with a highly rhombic S = 3/2 signal (see SI).…”

“…Indeed, stronger imidazole donors have already been pursued as represented by complex 2 (Figure ). , Unfortunately, this specific complex suffers from aqueous insolubility from pH 7 to pH 11 due to charge neutralization by deprotonation of the cationic complex, complicating comparisons of its catalytic activity with the Py5-based system. A closely related ligand scaffold is the methylated analogue tip­(Me) (tip­(Me) = 2,6-(bis­(bis-2- N -methylimidazolyl)-hydroxymethyl)­pyridine), which was reported nearly 40 years ago, but has not been examined for water oxidation catalysis (complex 3 , Figure ).…”

Electrocatalytic Hydrogen Production with a Molecular Cobalt Complex in Aqueous Solution

“…The redox process was assigned to the electrochemically irreversible Co III|II redox couple. As expected, the redox potential of the Co III|II couple in 1 is lower than the one of B and C in water and D in MeOH/H 2 O …”

“…I. Siewert Universität Göttingen,Institut für Anorganische Chemie Tammannstr. 4,37077 Göttingen,Germany [b] [ 8] B, [9] C, [10] and D [12] with N 5 pyridine, pyrazole, and imidazole donor ligands.…”

“…L CF3 was fully characterized by the usual methods and its purity was confirmed by micro analysis. The 1 H-and 13 [ 8] B, [9] C, [10] and D [12] with N 5 pyridine, pyrazole, and imidazole donor ligands.…”