Synthesis, structure, and hydrogen evolution studies of a heteroleptic Co(III) complex

• Published in: Inorganica Chimica Acta Vol. 517; p. 120195
• Main Authors: Celestine, Michael J., Lawrence, Mark A.W., Schott, Olivier, Picard, Vincent, Hanan, Garry S., Marquez, Emily M., Harold, Chekeyl G., Kuester, Cole T., Frenzel, Blaise A., Hamaker, Christopher G., Hightower, Sean E., McMillen, Colin D., Holder, Alvin A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2021; Elsevier Science Ltd
• Subjects: Acetonitrile; Cobalt(III); Crystal structure; Crystallography; Density functional theory; Electrocatalysis; Electrolysis; Hydrogen; Hydrogen evolution; Hydrogen production; Photocatalysis; Polypyridyl ligands; Silver chloride; Electrocatalysis; Polypyridyl ligands; Cobalt(III); Photocatalysis; Hydrogen production
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2020.120195

The cobalt(III) complex, mer-[Co(tpy)(phen)Cl](PF6)2, was synthesized via a one-pot synthesis and fully characterised; then utilised to photocatalytically produce hydrogen under acidic conditions. [Display omitted] •A cobalt(III) complex, [Co(tpy)(phen)Cl](PF6)2, was synthesized and characterized.•The crystal structure has a monoclinic crystal system with a C2/c space group.•The complex displayed good electrocatalytic and photocatalytic properties.•A turnover frequency of 3300 mmol H2 mol-1CAT min−1 was observed over a 3 h period. [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN (where tpy = 2,2′;6′,2″-terpyridine and phen = 1,10-phenanthroline) was prepared from a one pot mixture involving stoichiometric quantities of tpy and phen. The structure of [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN was confirmed by elemental analysis, high resolution mass spectroscopy (HRMS), various spectroscopic analyses, and X-ray crystallography. Density functional theory calculations were also carried out. The crystal structure of [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN, which was grown from acetonitrile, revealed a monoclinic crystal system with a C2/c space group. The cyclic voltammogram which was acquired in acetonitrile revealed reversible CoIII/II, CoII/I, and CoI/0 mixed with ligand-based redox couples at E½ = +0.35, –0.81, and –1.37 V (vs Ag/AgCl), respectively. In the presence of p-cyanoanillinium tetrafluoroborate with acetonitrile as the solvent, [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN displayed electrocatalytic hydrogen evolution activity at a 830 mV overpotential, as evidenced by a catalytic wave which was observed in the voltammogram, and by the detection of hydrogen in the headspace of the reaction vessel of a controlled potential electrolysis experiment. Photocatalytic hydrogen evolution studies with [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN produced a turnover frequency (TOF) of 3300 mmol H2 mol−1CAT min−1 when compared to [Co(dmgH)2(py)Cl] (where dmgH = dimethylglyoximato), which had a TOF of 4500 mmol H2.mol−1CAT min−1 under the same conditions. [Co(tpy)(phen)Cl](PF6)2•0.25CH3CN produced a turnover number (TON) of 79 when compared to 141 for [Co(dmgH)2Cl(py)] in DMF in ca 3 h.