Sodium-coupled electron transfer reactivity of metal–organic frameworks containing titanium clusters: the importance of cations in redox chemistry

Saouma, Caroline T.; Tsou, Chingfu; Richard, S.B.; Ameloot, Rob; Vermoortele, Frederik; Smolders, Simon; Bueken, Bart; DiPasquale, Antonio G.; Kaminsky, Werner; Valdez, Carolyn N.; Vos, Dirk De; Mayer, James M.

doi:10.1039/c8sc04138e

Cited by 28 publications

(32 citation statements)

References 38 publications

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“…Because photodoping of Ti-MOFs involves trapping an electron as Ti 3+ and the liberation of H + , the e --H + pair has the potential to recombine as H2, but energetic aspects of the process ensures that it does not. These results support several hypotheses put forward by the Mayer43 and Martí-Gastaldo 42 labs, and own: First, the calculated geometry of H + -MUV-10(Ca) indicates localization of H + on bridging oxos and, second, concomitant stabilization of Ti-based conduction-band potentials. Importantly, the in situ measurement of EF through an optical redox indicator places the steady-state redox potential of photodoped MUV-10(Ca) below the HER electrochemical potential at comparable H + concentrations, providing an energetic justification for the ability of Ti-MOFs to photodope.…”

supporting

confidence: 87%

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

Fabrizio¹,

Lazarou²,

Payne³

et al. 2021

Preprint

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<div> <div> <div> <p>Titanium-based metal—organic frameworks (Ti-MOFs) attract intense research attention because they can store charges in the form of Ti3+ and they serve as photosensitizers for co-catalysts through heterogeneous photoredox reactions at the MOF-liquid interface. Both charge storage and charge transfer depend on redox potentials of the MOF and the molecular substrate, but the factors controlling these energetic aspects are not well understood. Additionally, photocatalysis involving Ti-MOFs relies on co-catalysts rather than the intrinsic Ti reactivity in part because Ti-MOFs with open metal sites are rare. Here, we report that the class of Ti-MOFs known as MUV-10 can be synthetically modified to include a range of redox-inactive ions with flexible coordination environments that control the energies of the photoactive orbitals. Lewis </p> <p>acidic cations installed in the MOF cluster (Cd, Sr , and Ba ) or introduced to the pores (H, Li, Na, K) tune the electronic structure and band gaps of the MOFs. Through use of optical redox indicators, we report the first direct measurement of the Fermi levels (redox potentials) of photoexcited MOFs in situ. Taken together, these results explain the ability of Ti-MOFs to store charges and provide design principles for achieving heterogeneous photoredox chemistry with electrostatic control.</p> </div> </div> </div>

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supporting

confidence: 87%

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

Fabrizio¹,

Lazarou²,

Payne³

et al. 2021

Preprint

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“…Further, inherent MOF porosity facilitates valuable trapping of the low‐valent titanium species through bulk reduction of the framework by small molecules in the pore. Addition of up to eight electrons per node can be achieved in the presence of charge stabilizing counterions …”

mentioning

confidence: 99%

Titanium(IV) Inclusion as a Versatile Route to Photoactivity in Metal–Organic Frameworks

Mancuso

Hendon

2019

Advcd Theory and Sims

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Titanium-containing metal-organic frameworks (MOFs) are known to perform light-promoted chemical transformations. Formation of these frameworks, accessed either natively or via transmetallation, can instill beneficial photocatalytic properties in previously photo-inert scaffolds. Band edge diagrams coupled with their density of states illustrate the persistent nature of the accessible titanium d-states at the conduction band edge, independent of linker identity. In essentially all of these Ti-containing frameworks, the valence band edge localizes on the organic component, permitting facile modulation of the band gap. In sum, the spatial separation of photogenerated excitons will be observed in both the native and titanium(IV)-substituted MOFs, and this exciton pair is useful in photocatalysis.

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“…In a similar vein, the Mayer group, has justified the charge storage capacity of titanium cluster MOFs in terms of cation-oxo electrostatic pairing stabilization. 43,44 Although MIL-125 nodes contain eight titanium centers, steady-state photoirradiation does not lead to quantitative reduction of all metal ions to Ti 3+ , as evidenced by electron paramagnetic spectroscopy (EPR). Treatment of MIL-125 particles with sodium-based reductants, however, increases the average number of reduced metal ions per MIL-125 cluster, suggesting a strong cation-dependence and ion-pairing effect of charge storage in titanium MOFs.…”

Section: Introductionmentioning

confidence: 99%

“…Treatment of MIL-125 particles with sodium-based reductants, however, increases the average number of reduced metal ions per MIL-125 cluster, suggesting a strong cation-dependence and ion-pairing effect of charge storage in titanium MOFs. 43 The photoredox chemistry of MOFs, therefore, depends strongly on the chemical factors that control the electrochemical potentials of the resulting photoexcited charges. We therefore seek Ti-MOFs with OMSs and synthetic tunability for investigating the chemical factors that control photoredox activity.…”

Section: Introductionmentioning

confidence: 99%

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

Fabrizio¹,

Lazarou²,

Payne³

et al. 2021

Preprint

View full text Add to dashboard Cite

<div> <div> <p>Titanium-based metal—organic frameworks (Ti-MOFs) attract intense research attention because they can store charges in the form of Ti3+ and they serve as photosensitizers for co-catalysts through heterogeneous photoredox reactions at the MOF-liquid interface. Both charge storage and charge transfer depend on redox potentials of the MOF and the molecular substrate, but the factors controlling these energetic aspects are not well understood. Additionally, photocatalysis involving Ti-MOFs relies on co-catalysts rather than the intrinsic Ti reactivity in part because Ti-MOFs with open metal sites are rare. Here, we report that the class of Ti-MOFs known as MUV-10 can be synthetically modified to include a range of redox-inactive ions with flexible coordination environments that control the energies of the photoactive orbitals. Lewis acidic cations installed in the MOF cluster (Cd, Sr , and Ba ) or introduced to the pores (H, Li, Na, K) tune the electronic structure and band gaps of the MOFs. Through use of optical redox indicators, we report the first direct measurement of the Fermi levels (redox potentials) of photoexcited MOFs in situ. Taken together, these results explain the ability of Ti-MOFs to store charges and provide design principles for achieving heterogeneous photoredox chemistry with electrostatic control.</p> </div> </div>

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Sodium-coupled electron transfer reactivity of metal–organic frameworks containing titanium clusters: the importance of cations in redox chemistry

Abstract: Storage of electrons in the Ti8O8 nodes of MOF MIL-125 is controlled by the presence of charge-balancing Na+ cations.

Cited by 28 publications

References 38 publications

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

Titanium(IV) Inclusion as a Versatile Route to Photoactivity in Metal–Organic Frameworks

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

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