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Franco LR, Toledo KCF, Matias TA, Araujo CM, Araki K, Coutinho K. Theoretical investigation of solvent and oxidation/deprotonation effects on the electronic structure of a mononuclear Ru-aqua-polypyridine complex in aqueous solution. Phys Chem Chem Phys 2023; 25:24475-24494. [PMID: 37655780 DOI: 10.1039/d3cp02154h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
Mononuclear polypyridine ruthenium (Ru) complexes can catalyze various reactions, including water splitting, and can also serve as photosensitizers in solar cells. Despite recent progress in their synthesis, accurately modeling their physicochemical properties, particularly in solution, remains challenging. Herein, we conduct a theoretical investigation of the structural and electronic properties of a mononuclear Ru-aqua polypyridine complex in aqueous solution, considering five of its possible oxidation/protonation states species: [RuII(H2O)(py)(bpy)2]2+, [RuII(OH)(py)(bpy)2]+, [RuIII(H2O)(py)(bpy)2]3+, [RuIII(OH)(py)(bpy)2]2+ and [RuIV(O)(py)(bpy)2]2+, where py = pyridine and bpy = 2,2'-bipyridine. At first, we investigate the impact of proton-coupled and non-coupled electron transfer reactions on the geometry and electronic structure of the complexes in vacuum and in solution, using an implicit solvent model. Then, using a sequential multiscale approach that combines quantum mechanics and molecular mechanics (S-QM/MM), we examine the explicit solvent effects on the electronic excitations of the complexes, and compare them with the experimental results. The complexes were synthesized, and their absorption spectra measured in aqueous solution. To accurately describe the QM interactions between the metal center and the aqueous ligand in the MM simulations, we developed new force field parameters for the Ru atom. We analyze the solvent structure around the complexes and account for its explicit influence on the polarization and electronic excitations of the complexes. Notably, accounting for the explicit solvent polarization effects of the first solvation shells is essential to correctly describe the energy of the electronic transitions, and the explicit treatment of the hydrogen bonds at the QM level in the excitation calculations improves the accuracy of the description of the metal-to-ligand charge-transfer bands. Transition density matrix analysis is used to characterize all electronic transitions in the visible and ultraviolet ranges according to their charge-transfer (CT) character. This study elucidates the electronic structure of those ruthenium polypyridyl complexes in aqueous solution and underscores the importance of precisely describing solvent effects, which can be achieved employing the S-QM/MM method.
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Affiliation(s)
- Leandro Rezende Franco
- Instituto de Fisica, Universidade de Sao Paulo, Cidade Universitaria, 05508-090 Sao Paulo, SP, Brazil
- Department of Engineering and Physics, Karlstad University, 65188 Karlstad, Sweden.
| | | | - Tiago Araujo Matias
- Instituto de Quimica, Universidade de Sao Paulo, Av. Lineu Prestes 748, Butanta, 05508-000 Sao Paulo, SP, Brazil
| | - C Moyses Araujo
- Department of Engineering and Physics, Karlstad University, 65188 Karlstad, Sweden.
- Materials Theory Division, Department of Physics and Astronomy, Ångström Laboratory, Uppsala University, 75120 Uppsala, Sweden
| | - Koiti Araki
- Instituto de Quimica, Universidade de Sao Paulo, Av. Lineu Prestes 748, Butanta, 05508-000 Sao Paulo, SP, Brazil
| | - Kaline Coutinho
- Instituto de Fisica, Universidade de Sao Paulo, Cidade Universitaria, 05508-090 Sao Paulo, SP, Brazil
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Ghaderian A, Kazim S, Khaja Nazeeruddin M, Ahmad S. Strategic factors to design the next generation of molecular water oxidation catalysts: Lesson learned from ruthenium complexes. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2021.214256] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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