Efficient energy conversion is a research area necessary to address the grown demand of energy utilization. In the natural photosystem, the high efficiency of solar energy utilization is contingent on the ensemble chromophore behavior. To mimic a well-defined chromophore arrangement achieved in nature, the molecular self-assembly process for effective design of artificial light-harvesting arrays should be utilized. Such control of the chromophore order can be achieved in metal-organic frameworks, which possess a high degree of structural and chemical tunability, imposing a very few restrictions on the chromophore of choice. We built novel well-defined fulleretic and photochromic materials with a predesigned pathway for the energy transfer.^1–3 The prepared systems allow us to control the excited state decay pathways in the large light-harvesting array through alternation of an excitation wavelength. Upon further development, we envision that the prepared well-defined hybrid materials could foreshadow a new avenue for the engineering of new sensors, solar cells, or light-emitting diodes in the future.

References:

1. Fellows, B. W.; Rice, A. M; Williams, D. E.; Dolgopolova, E. A.; Vannucci, A. K.; Pellechia, P.J.; Smith, M. D.; Krause, J. A.; Shustova, N. B. Angew. Chem. Int. Ed. 2016, 55, 2195–2199.
2. Williams, D. E.; Godfrey, D. C.; Ermolaeva, E. D. Pellechia, P. J.; Greytak, A. B.; Smith, M. D.; Avdoshenko, S. M; Popov, A. A.; Shustova, N. B. Angew. Chem. Int. Ed. 2016, 55, 9070–9074.
3. Williams, D. E.; Dolgopolova, E. A.; Pellechia, P.J.; Palukoshka, A.; Wilson, T. J.; Tan, R.; Maier, J. M.; Tan, R.; Greytak, A. B.; Smith, M. D.; Krause, J. A.; Shustova, N. B J. Am. Chem. Soc. 2015, 137, 2223–2226.

In seawater, Uranium exists in ppb concentrations; estimates show that if 1% was extracted, the current U reserves would see a tenfold increase. Polymeric amidoximes have dominated the literature as uranium sequesters; they were initially suggested in the 1980s and later field-tested, retrieving 1 kg of U from the Pacific Ocean. Oximes (>C=N–OH) are known to be strong α-nucleophiles and very effective ligands for binding to transition metal and lanthanide ions. From the use of 2,6-diacetylpyridine dioxime (dapdoH₂) in uranyl chemistry, a stable uranyl dimeric complex resulted, namely [(UO₂)₂Cl₂(dapdoH)₂]. The latter was studied with single-crystal x-ray crystallography, IR, NMR, absorption, fluorescence, and Raman spectroscopies, cyclic voltammetry, mass spectrometry, as well as DFT calculations. The ESI-MS and NMR data suggest that the complex is stable in solution, and the in-silico studies proved that dapdoH₂ has a strong affinity for the uranyl cation. DFT studies were also used to investigate the electronic and vibrational properties of the complex, and data closely modeled the experimental Raman spectra.

The use of interpenetration in metal organic frameworks (MOFs) has many added benefits with improvement in the robustness of the material, stepwise gas adsorption and selective adsorption. The control of the degree of interpenetration is further important has it has the advantage of enhancing the efficiency of the MOF through modulation of the pores. Partial interpenetration is rare in MOFs and can reduce the free space and increase the selectivity. Here we report on one such partially interpenetrated MOF, Cu₂(pbpta) where H₄pbpta = 4,4’,4”,4”’-(1,4-phenylenbis(pyridine-4,2-6-triyl))-tetrabenzoic acid. This material is the first example of a partially interepenetrated MOF with NbO topology and exhibits selective adsorption of CO₂ and other heavier alkanes over CH₄.  The Cu₂(pbpta)  has a high BET surface area of 2537 m²/g and additionally shows good catalytic efficacy for the conversion of CO₂ into industrially important cyclic carbonates through cycloaddition with epoxides.

The divalent group 12 metal ions are widely used to catalyze reactions of unsaturated C–C bonds, with the formation of metal–π-complexes commonly proposed as important intermediates. Despite these proposals, little experimental evidence exists to support the stability and reactivity of such adducts for the group 12 metals.  To shed light on the stability and potential reactivity of these intermediates, we have used density functional theory to investigate the bonding and activation of alkenes by Zn²⁺, Cd²⁺, and Hg²⁺ in a series of [M(L)(η²–C₂H₄)]ⁿ⁺ complexes (where L = a variety of N-donor ligands). Structural and vibrational analyses predict an activated ethylene C=C bond with all three metals, with the degree of activation enhanced by the use of neutral bidentate ligands . Bond energy decomposition analysis (EDA) shows that metal–ethylene interaction energies are favorable for all complexes studied and even more favorable than for many experimentally-isolated copper(I) analogues. Both EDA and natural bond orbital (NBO) analysis indicate that ethylene(π)→[M(L)]ⁿ⁺ electron donation dominates Dewar-Chatt-Duncanson bonding in these complexes, while electrostatic and orbital stabilization provide roughly equal contributions to the overall metal–ethylene bond stabilization. Molecular orbital analysis predicts that the electrophilic reactivity of the metal-bound ethylene moiety would be significantly enhanced due to substantial stabilization of its π*- and π-orbitals. These findings support reported experimental results and provide new insight into the use of group 12 metals as catalysts in important organic transformations.

Multi-metallic clusters are often employed in biological systems to facilitate electron transfer and assist in the activation of strong bonds in small molecules. Recently, we have synthesized and fully characterized a pair of chalcogenide-bridged tricopper complexes LCu₃(μ₃-E)  (E = S, Se),   models of Cu_z clusters in N₂O reductase (where L is a cyclophane featuring three b-diketiminate arms). Both complexes can be reduced by one electron to afford the S=1/2 M[LCu₃(μ₃-E)], where M = Cp^*₂Co⁺, K(THF)_n⁺, (18-crown-6)K(THF)₂⁺. The unpaired electron is delocalized over the {Cu₃(μ₃-E} cluster, with the DFT suggesting that the electron density residing mostly on E donor. Remarkably, these radical anion complexes function as reductants towards a variety of small molecule substrates, including CO₂, to regenerate the neutral starting reagent, LCu₃(μ₃-E).  Ongoing mechanistic and electrochemical studies for CO₂­ reduction, including the role of the counter-cation, will be discussed.

The gradual accumulation of carbon dioxide (CO₂) is considered a large contributing factor in the overall increase of global temperature in recent years due to human activity. In this work, a systematic approach was taken to functionalize a series of metal-organic frameworks (MOFs) isoreticular to MIL-125-NH₂ to act as photocatalyts in the transformation of CO₂ into reduced carbon in solar fuels. The prepared materials display a reduction in optical band gap correlated to inductive effects from increasing N-alkyl substituents chain lengths (from methyl to heptyl). We found that secondary N-alkyl substitution (isopropyl, cyclopentyl and cyclohexyl) display larger apparent quantum yields that of the primary analogues in the photoreduction of CO₂ under irradiation with blue LED light. This demonstrates a promising new type of candidate materials for next generation visible-light photocatalyst constructed from earth abundant elements.