Direct Spectroscopic Detection of a Zwitterionic Excited State

Engebretson, Daniel; Zaleski, Jeffrey M.; Leroi, G. E.; Nocera, Daniel G.

doi:10.1126/science.265.5173.759

Cited by 33 publications

(25 citation statements)

References 35 publications

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“…This experimental challenge was overcome with the two-electron bond of quadruple-bonded metal-metal complexes. Anchored by a 2 4 framework and sterically locking ligands, the four states of the two-electron bond, 1 , 3 *, 1 * and 1 **, were experimentally defined for dimolybdenum quadruple-bond complexes (Engebretson et al 1994(Engebretson et al , 1999Cotton & Nocera, 2000). Within the group of dimolybdenum quadruple-bond complexes, the tetraacetates are exemplars.…”

Section: Chemical Contextmentioning

confidence: 99%

Crystal structure of a trifluoromethyl benzoato quadruple-bonded dimolybdenum complex

et al. 2022

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The study of quadruple bonds between transition metals, in particular those of dimolybdenum, has revealed much about the two-electron bond. The solid-state structure of the quadruple-bonded dimolybdenum(II) complex tetrakis(μ-4-trifluoromethylbenzoato-κ2 O:O′)dimolybdenum(II) 0.762-pentane 0.238-tetrahydrofuran solvate, [Mo2(p-O2CC6H4CF3)4·2THF]·0.762C5H12·0.238C4H8O or [Mo2(C8H4F3O2)4(C4H8O)2]·0.762C5H12·0.238C4H8O is reported. The complex crystallizes within a triclinic cell and low symmetry (P\overline{1}) results from the intercalated pentane/THF solvent molecules. The paddlewheel structure at 100 K has inversion symmetry and comprises four bridging carboxylate ligands encases the Mo2(II,II) core that is characterized by two axially coordinated THF molecules and an Mo—Mo distance of 2.1098 (7) Å.

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Section: Chemical Contextmentioning

confidence: 99%

Crystal structure of a trifluoromethyl benzoato quadruple-bonded dimolybdenum complex

et al. 2022

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“…However, the 1 A 1g 1 A 1g * transition is allowed in the two-photon absorption spectrum. 193,194 Here, two electrons are promoted to the * level by the simultaneous absorption of two photons whose energies sum to the energy required. Because we can estimate the 1 A 2u, it follows that the two exciting photons must be in the near-infrared frequency range.…”

Section: Details Of the Manifold Of Statesmentioning

confidence: 99%

Physical, Spectroscopic and Theoretical Results

Cotton

2005

Multiple Bonds Between Metal Atoms

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Structural Correlations Bond orders and bond lengthsThroughout the preceding chapters of this book we have reported and in some cases discussed the lengths of the multiple bonds between metal atoms. We have reported in tabular form most of the M-M distances that have been determined crystallographically. It is now time to make some general comments on these distances in relation to our understanding of the M-M bonds.It is a general qualitative rule in chemistry that bond lengths and bond orders are inversely related. In some limited areas, particularly with the fi rst-row elements carbon, nitrogen, and oxygen, quantitative relationships expressing bond length as a single-valued function of bond order are well known. However, these quantitative relationships are based heavily on faith, as well as fact. Bond lengths are facts; bond orders are not. In the process of inferring a bond order from a bond length one is often getting out no more than what was put in to begin with.We shall not further digress into a discussion of the philosophical ambiguities of these quantitative bond order-bond length correlations because they have proven to be useful, within their own sphere of application. However, there is no a priori reason to expect that similar procedures will (or will not!) work in the very different realm of metal-to-metal bonds. Experience is the only test, and experience thus far has shown that M-M bonds cannot usefully be treated in such a way.In the realm of M-M bonds it is best to invoke only a qualitative inverse relationship between bond order and bond length and to defi ne bond order only in a qualitative or ordinal way. In this book we have used the term M-M bond order only to indicate how many electron pairs are believed, on the basis of essentially qualitative considerations, to play a signifi cant part in holding the pair of metal atoms together. We condemn as foolish and hopeless any effort to associate a unique, precise, quantitative bond order with each and every M-M internuclear distance.In principle, M-M bond lengths, like others, should be amenable to treatment by the method of molecular mechanics, and some efforts [1][2][3][4] (hampered by a dearth of necessary experimental data) to do this have been reported. In general the results are encouraging and can account for

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“…A paddlewheel Mo 2 complex has an electronic configuration of σ 2 π 4 δ 2 ground state, as described in Figure , with two d electrons paired in the high-energy bonding orbital (δ). The δ → δ* transition energy falls in a narrow range of 400–550 nm, and thus, the low-lying excited state, σ 2 π 4 δ 1 (δ*) 1 , simply denoted δδ*, , can be generated upon illumination by visible light . The multiply bonded Mo 2 complexes may act as an electron source or sink, depending on its oxidation state or bond order, in the oxidation–reduction process by providing or accepting electrons accompanied with δ bond breakage or formation. , In nonaqueous solutions, the singlet δδ* excited state has sufficiently long lifetime to participate in photochemical reactions, , unlike single metal complexes whose long-lived excited state results from intersystem conversion that reduces the quantum efficiency.…”

Section: Introductionmentioning

confidence: 99%

Making Use of the δ Electrons in K₄Mo₂(SO₄)₄ for Visible-Light-Induced Photocatalytic Hydrogen Production

Liu

Zhu

et al. 2019

ACS Appl. Mater. Interfaces

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Quadruply bonded dimolybdenum complexes with a σ 2 π 4 δ 2 electronic configuration for the ground state have rich metal-centered photochemistry. An earlier study showed that stoichiometric or less amount of molecular hydrogen was produced upon irradiation by ultraviolet light (λ = 254 nm) of K 4 Mo 2 (SO 4 ) 4 in sulfuric acid solution, which was attributed to the reductive capability of the ππ* excited state. To make use of the δ electrons for visible-light-induced photocatalytic hydrogen evolution, a multicomponent heterogeneous photocatalytic system containing K 4 Mo 2 (SO 4 ) 4 photosensitizer, TiO 2 electron relay, and MoS 2 cocatalyst is designed and tested. With ascorbic acid added as a sacrificial reagent, irradiation by artificial sunlight (AM 1.5) on the reaction in 5 M H 2 SO 4 has produced 13 400 μmol g −1 of molecular hydrogen (based on the Mo 2 complex), which is 30 times higher than the hydrogen yield obtained from the reaction of bare K 4 Mo 2 (SO 4 ) 4 with H 2 SO 4 under ultraviolet light irradiation. Further improvement of hydrogen evolution is achieved by addition of oxalic acid, along with an electron donor, which gives an additional 50% increase in H 2 yield. Spectroscopic analyses indicate that, in this case, a junction between the Mo 2 complex and TiO 2 is built by the oxalate bridging ligand, which facilitates charge injection and separation from the Mo 2 core. This Mo 2 −TiO 2 −MoS 2 system has achieved a high hydrogen evolution rate up to 4570 μmol g −1 h −1 . The efficiency of K 4 Mo 2 (SO 4 ) 4 as a metal-centered photosensitizer is also proved by parallel experiments with a dye chromophore, fluorescein, which presents comparable H 2 yields and hydrogen evolution rates. Most importantly, in this study, detailed analyses illustrate that the photocatalytic cycle with hydrogen gas as an outcome of the reaction is established by involvement of the δδ* excited state generated by visible light irradiation. Therefore, this work shows the potential of quadruply bonded Mo 2 complexes as photosensitizers for photocatalytic hydrogen evolution.

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Direct Spectroscopic Detection of a Zwitterionic Excited State

Cited by 33 publications

References 35 publications

Crystal structure of a trifluoromethyl benzoato quadruple-bonded dimolybdenum complex

Crystal structure of a trifluoromethyl benzoato quadruple-bonded dimolybdenum complex

Physical, Spectroscopic and Theoretical Results

Making Use of the δ Electrons in K₄Mo₂(SO₄)₄ for Visible-Light-Induced Photocatalytic Hydrogen Production

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Direct Spectroscopic Detection of a Zwitterionic Excited State

Cited by 33 publications

References 35 publications

Crystal structure of a trifluoromethyl benzoato quadruple-bonded dimolybdenum complex

Crystal structure of a trifluoromethyl benzoato quadruple-bonded dimolybdenum complex

Physical, Spectroscopic and Theoretical Results

Making Use of the δ Electrons in K4Mo2(SO4)4 for Visible-Light-Induced Photocatalytic Hydrogen Production

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Making Use of the δ Electrons in K₄Mo₂(SO₄)₄ for Visible-Light-Induced Photocatalytic Hydrogen Production