Ab-Initio Molecular Orbital Studies of Structure and Reactivity of Transition Metal-OXO Compounds

Yamaguchi, Kizashi; Takahara, Yoichi; Fueno, Takayuki

doi:10.1007/978-94-009-4746-7_11

Cited by 349 publications

(227 citation statements)

References 37 publications

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“…The nature of high-valent metal-oxo species is labile as shown in our early paper (45). The high-valent MnðVÞ═O bond formally has a triple bond in the sense of the simple MO theory.…”

Section: Possible Electronic and Spin States Of Mononuclear And Binucmentioning

confidence: 89%

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

Tanaka

Isobe

Yamanaka

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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The nature of chemical bonds of ruthenium(Ru)-quinine(Q) complexes, mononuclear ½RuðtrpyÞð3,5-t-Bu 2 QÞðOH 2 Þ ðClO 4 Þ 2 (trpy ¼ 2,2 0 : 6 0 ,2 0 0 -terpyridine, 3,5-di-tert-butyl-1,2-benzoquinone) (1), and binuclear ½Ru 2 ðbtpyanÞð3,6-di-Bu 2 QÞ 2 ðOH 2 Þ 2þ ðbtpyan ¼ 1,8-bisð2,2 0 : 6 0 ,2 0 0 -terpyrid-4 0 -ylÞanthracene, 3,6-t-Bu 2 Q ¼ 3,6-di-tertbutyl-1,2-benzoquinone) (2), has been investigated by broken-symmetry (BS) hybrid density functional (DFT) methods. BS DFT computations for the Ru complexes have elucidated that the closed-shell structure (2b) Ru(II)-Q complex is less stable than the open-shell structure (2bb) consisting of Ru(III) and semiquinone (SQ) radical fragments. These computations have also elucidated eight different electronic and spin structures of tetraradical intermediates that may be generated in the course of water splitting reaction. The Heisenberg spin Hamiltonian model for these species has been derived to elucidate six different effective exchange interactions (J) for four spin systems. Six J values have been determined using total energies of the eight (or seven) BS solutions for different spin configurations. The natural orbital analyses of these BS DFTsolutions have also been performed in order to obtain natural orbitals and their occupation numbers, which are useful for the lucid understanding of the nature of chemical bonds of the Ru complexes. Implications of the computational results are discussed in relation to the proposed reaction mechanisms of water splitting reaction in artificial photosynthesis systems and the similarity between artificial and native water splitting systems.four redox center | manganese clusters | water oxidation | oxyl radical | O-O bond formation P hotosynthesis is one of the most important chemical processes on our planet. Extensive experimental studies (1-6) on the process have revealed that oxygenic photosynthesis involves several protein-cofactor complexes embedded in the photosynthetic thylakoid membranes of plants, green algae, and cyanobacteria. Among these complexes, photosystem II (PSII) has a prominent role because it catalyzes the oxidation of water (, which is the prerequisite for all aerobic life. The main cyclic process to catalyze the water-oxidation consists of successive four steps, which is referred to as the Kok cycle (6). During this process, the oxygen-evolving complex (OEC), the catalyst of the water oxidation reaction, takes five oxidation states (S 0 -S 4 ). The OEC in PSII contains an inorganic cluster consisting of four manganese ions and one calcium ion that are bridged by at least five oxygens; the active site is therefore expressed with the CaMn 4 O 5 cluster (3) (5). Very recently, the electronic structure and reactivity of 3 (7-10) have been elucidated based on the new high-resolution X-ray structure (5).In the past decades, a number of experimental and theoretical studies (11-29) have been performed to design artificial photosynthetic systems that mimic native PSII systems. Many binuclear transition-metal catalysts s...

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“…The nature of high-valent metal-oxo species is labile as shown in our early paper (45). The high-valent MnðVÞ═O bond formally has a triple bond in the sense of the simple MO theory.…”

Section: Possible Electronic and Spin States Of Mononuclear And Binucmentioning

confidence: 89%

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

Tanaka

Isobe

Yamanaka

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…These working hypotheses (WH1-WH8), together with present and previous computational results [33,[53][54][55] can be used for consideration of possible mechanisms of water splitting reaction at OEC of PSII: note that the formation of MnOAOH is a reverse process of its heterolysis(or homolysis):…”

Section: Electron Transfer Pathway Revealed By the X-ray Structurementioning

confidence: 99%

Possible mechanisms of water splitting reaction based on proton and electron release pathways revealed for CaMn₄O₅ cluster of PSII refined to 1.9 Å X‐ray resolution

Saitô

Yamanaka

Kanda

et al. 2011

Int J of Quantum Chemistry

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Recently, Umena et al. have revealed the X-ray diffraction structure of the CaMn 4 O 5 cluster in the oxygen evolving complex (OEC) of photosystem II (PSII) refined to 1.9 Å resolution. Their X-ray structure has first elucidated hydrogen-bonding networks and proton release pathways at OEC of PSII. Here, several working hypotheses Additional Supporting Information may be found in the online version of this article Correspondence to: S. Yamanaka; e-mail: syama@chem.sci.osaka-u.ac.jp Contract grant sponsor: Grants-in-Aid for Scientific Research; Contract grant numbers: 19750046, 19350070, 18350008, 23550016 (heuristic principles) for water splitting reaction are derived from their X-ray structure for theoretical modeling. These hypotheses suggest how water can be oxidized at OEC of PSII: namely possible reaction mechanisms for the reaction. To confirm them, we have also performed broken-symmetry (BS) UB3LYP calculations for active site models based on their XRD structure. The bond lengths of formal Mn(V)AO with labile dp-pp bonds are optimized to clarify possible roles of the species that are often introduced as a key intermediate in the catalytic (Kok) cycle for water splitting reaction at OEC of PSII. Location of the transition structure for the oxygen-oxygen (OAO) bond formation is also performed by the energy optimization technique. The natural orbital (NO) analysis of the UB3LYP solutions has been performed to obtain the natural molecular orbitals and their occupation numbers that have been useful for classification of localized d-electrons, labile chemical bonds and closed-shell (valence) orbitals. The localized d-electrons characterized by the NO analysis are the origins for the magnetism revealed by ENDOR and other magnetic experiments. On the other hand, the nature of labile (soft) dp-pp bonds responsible for the OAO bond formation has been investigated on the basis of chemical indices such as effective bond order (b), diradical character (y), and spin density (Q) indices that are calculated using the orbital overlap between broken-symmetry orbitals. These chemical indices have been calculated for the transition structure of the OAO bond formation at OEC of PSII. Implications of present computational results are discussed in relation to the derived hypotheses and available accumulated experimental results.

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“…Then the magnitude of J is a measure of transition temperature for our J model of superconductivity. 71 Before the discovery of the high Tc cuprates by Bednort and Muller, 72 our UHF calculations of MOM units 39 have indicated that the magnitude of J value for the CuOCu unit is one-order larger than those of other transition metal oxides. Therefore, after the discovery of the material, we immediately presented our J-model for the high-T c superconductivity (T c = cJ, c = constant) on the basis of the spin fluctuation mechanism.…”

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 98%

“…The spin Hamiltonian model at the quantum limit (Jz = 0 and [38][39][40][41][42] For the purpose, the spin-unrestricted HartreeFock (UHF) wavefunctions for the classical spin alignments I and II (see Fig. 3) with the antiferromagnetic order are constructed, respectively, as…”

Section: A Thoretical Background (I) Magnetic Ringsmentioning

confidence: 99%

“…Then the BCS wavefunction is rewritten by the pseudo spins as (39) The superconducting (SC) state is formally regarded as the helical spin density wave (HSDW) state, which is written by the general spin orbital (GSO), ψ = uk α + vk β, while the normal state is expressed by the uniaxial spins as illustrated in Figure 10. Thus the pseudo spin model is useful for pictorial understanding of the SC state in analogy of the spin aligments.…”

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

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Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

2003

Bulletin of the Korean Chemical Society

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A unified picture for magnetism, superconductivity, quantum optics and other properties of molecule-based materials has been presented on the basis of effective model Hamiltonians, where necessary parameter values have been determined by the first principle calculations of cluster models and/or band models. These properties of the matetials are qualitatively discussed on the basis of the spin and pseudo-spin Hamiltonian models, where several quantum operators are expressed by spin variables under the two level approximation. As an example, ab initio broken-symmetry DFT calculations are performed for cyclic magnetic ring constructed of 34 hydrogen atoms in order to obtain effective exchange integrals in the spin Hamiltonian model. The natural orbital analysis of the DFT solution was performed to obtain symmetry-adapted molecular orbitals and their occupation numbers. Several chemical indices such as information entropy and unpaired electron density were calculated on the basis of the occupation numbers to elucidate the spin and pair correlations, and bonding characteristic (kinetic correlation) of this mesoscopic magnetic ring. Both classical and quantum effects for spin alignments and singlet spin-pair formations are discussed on the basis of the true spin Hamiltonian model in detail. Quantum effects are also discussed in the case of superconductivity, atom optics and quantum optics based on the pseudo spin Hamiltonian models. The coherent and squeezed states of spins, atoms and quantum field are discussed to obtain a unified picture for correlation, coherence and decoherence in future materials. Implications of theoretical results are examined in relation to recent experiments on molecule-based materials and molecular design of future molecular soft materials in the intersection area between molecular and biomolecular materials.

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Ab-Initio Molecular Orbital Studies of Structure and Reactivity of Transition Metal-OXO Compounds

Cited by 349 publications

References 37 publications

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

Possible mechanisms of water splitting reaction based on proton and electron release pathways revealed for CaMn₄O₅ cluster of PSII refined to 1.9 Å X‐ray resolution

Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

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Ab-Initio Molecular Orbital Studies of Structure and Reactivity of Transition Metal-OXO Compounds

Cited by 349 publications

References 37 publications

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

Possible mechanisms of water splitting reaction based on proton and electron release pathways revealed for CaMn4O5 cluster of PSII refined to 1.9 Å X‐ray resolution

Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

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Possible mechanisms of water splitting reaction based on proton and electron release pathways revealed for CaMn₄O₅ cluster of PSII refined to 1.9 Å X‐ray resolution