Review of DFT-simulated and experimental electrochemistry properties of the polypyridyl Row-1 Mn, Fe & Co, and Group-8 Fe, Ru and Os MLCT complexes

Predictable electronic tuning of FeII and RuII complexes via choice of azine: correlation of ligand pKa with Epa(MIII/II) of complex

“…The HOMO energies have also been calculated for the analogous family of [Os(L azine ) 3 ] 2+ complexes, and are seen to follow the same order as for the Fe II and Ru II complexes in terms of azine donor. The HOMO energy of each of the osmium complexes lies in between those of the respective iron and ruthenium analogues, which is not what was reported for the family of tris-ligated polypyridyl compounds studied by von Conradie et al 30,43,44,48 But we note that the Os II compounds in that study were optimised with a different basis set than had been used for the Fe II and Ru II analogues. Hence, herein, the HOMO energies of the literature tris-bipyridine family were recalculated using the same computational protocol (that used in the present study) for all three members (Fe II , Table 1 Summary of the electrochemical data (in V) obtained in dry acetonitrile with 0.1 M TBAPF 6 at 100 mV s −1 versus 0.01 M AgNO 3 |Ag, for the five Ru(II) tris-L azine complexes reported herein, along with those of the analogous Fe(II) complexes reported earlier.…”

“…This 'V-shaped' trend is typical for transition metal systems and agrees with previously reported experimental findings, that Os II typically has a lower E m than the other group 8 metal ions, and that Ru II typically has the highest E m . 44 Adiabatic IP was found to correlate better with E pa than the vertical IP, in both the Fe and Ru families, although both descriptors correlate very well. However, we want to note that the best correlation is obtained with the HOMO energies, demonstrating that Koopmans' theorem can indeed be utilized within DFT.…”

“…This ‘V-shaped’ trend is typical for transition metal systems and agrees with previously reported experimental findings, that Os II typically has a lower E m than the other group 8 metal ions, and that Ru II typically has the highest E m . 44…”

“…For a family of closely related complexes, first ionisation potentials have been shown in the literature to correlate with the experimentally determined E pa . 25,27,44 According to Koopmans' theorem, the first ionisation potential (IP) is equal to the negative orbital energy of the HOMO of a system, which enables a straightforward prediction of M III/II redox potentials from quantum chemical calculations due to error cancellation. 6,25,27,45,46 Although strictly only formulated for the Hartree-Fock method, it was shown that it can be applied to DFT even with better performance in some cases.…”

Computational Analysis of Low Overpotential Ammonia Oxidation by Metal–Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts

“…Varying the metal identity enables further control over [M 2 ] 4+/5+ redox potentials. In literature reports of redox potentials of analogous Ru and Os compounds, the latter are typically more cathodic by ∼500 mV, including in examples of metal–metal bonded compounds. − Relative to the calculated [Ru 2 ] 4+/5+ redox couples in 1–3NH 3 , the predicted potentials for the corresponding [Os 2 ] 4+/5+ redox couples of 4–6NH 3 lie substantially lower and approach or go beyond E NRR ° in acetonitrile of −0.94 V (Figure ). This drop in redox potential may effectively minimize η AOR if the Os 2 compounds display analogous chemical reactivity with ammonia to the catalytically active Ru 2 systems.…”