Comprehensive Thermodynamics of Nickel Hydride Bis(Diphosphine) Complexes: A Predictive Model through Computations
Prediction of thermodynamic quantities such as redox potentials and homolytic and heterolytic metal hydrogen bond energies is critical to the a priori design of molecular catalysts. In this paper we expound upon a density functional theory (DFT)-based isodesmic methodology for the accurate computation of the above quantities across a series of Ni(diphosphine)2 complexes compounds that are potential catalysts for production of H2 from protons and electrons, or oxidation of H2 to electrons and protons. Isodesmic schemes give relative free energies between the complex of interest and a reference system. A natural choice is to use as a reference a compound that shares similarities with the chemical species under study and for which the properties of interest have been measured with accuracy. However, this is not always possible as in the case of the Ni complexes considered here where data are experimentally available for only some species. To overcome this difficulty we employed a theoretical reference compound, Ni(PH3)4, which is amenable to highly accurate electron-correlated calculations, which allows one to explore thermodynamics properties even when no experimental input is accessible. The reliability of this reference is validated against the available thermodynamics data in acetonitrile solution. Overall the proposed protocol yields excellent accuracy for redox potentials (~ 0.10 eV of accuracy), for acidities (~1.5 pKa units of accuracy), for hydricities (~2 kcal/mol of accuracy), and for homolytic bond dissociation free energies (~ 1-2 kcal/mol of accuracy). The calculated thermodynamic properties are then analyzed for a broad set of Ni complexes. The power of the approach is demonstrated through the validation of previously reported linear correlations among properties. New correlations are revealed. It emerges that only two quantities, the Ni(II)/Ni(I) and Ni(I)/Ni(0) redox potentials (which are easily accessible experimentally), suffice to predict with high confidence the energetics of all relevant species involved in the catalytic cycles for H2 oxidation and production. The approach is extendable to other transition metal complexes. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1032401
- Report Number(s):
- PNNL-SA-81337; ORGND7; 44681; KC0307010; TRN: US201202%%21
- Journal Information:
- Organometallics, 30(22):6108-6118, Vol. 30, Issue 22; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
Similar Records
Cobalt-Group 13 Complexes Catalyze CO2 Hydrogenation Using a Co(-I)/Co(I) Redox Cycle
Relative hydride, proton, and hydrogen atom transfer abilities of [HM(diphosphine){sub 2}]PF{sub 6} complexes (M = Pt, Ni)