Engineering topics
Publications and source records attributed to Matson, Ellen M..
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The uranium-substituted thiomolybdate cluster, (Cp* 3 Mo 3 S 4 )UCp*, has been demonstrated as a model for water reduction by single uranium atoms supported on a molybdenum sulfide surface (U@MoS 2 ). In this study, the scope of O–H bond activation is expanded through the investigation of the reactivity of various alcohols with differing pKa values for the –OH proton. The reaction of (Cp* 3 Mo 3 S 4 )UCp* with stoichiometric amounts of methanol, phenol, 2,6-dichlorophenol, and nonafluoro-tert-butyl alcohol affords the corresponding mono-alkoxide species, (Cp* 3 Mo 3 S 4 )Cp*U(OR), via a uranium-metalloligand cooperative activation of the O–H bond. This observed reactivity is analogous to the O–H bond activation reported by (Cp* 3 Mo 3 S 4 )UCp* in the presence of water. However, addition of tert-butanol induces protonolysis of the Cp* ligand on uranium, resulting in the formation of a uranium tris-tert-butoxide cluster, (Cp* 3 Mo 3 S 4 )U(O t Bu) 3 . Independent synthesis of (Cp* 3 Mo 3 S 4 )Cp*U(O t Bu) was possible via an alternative pathway, eliminating sterics as a justification for the observed discrepancy in reactivity. Furthermore, these results offer insight into the role the –OH proton pKa plays in dictating the mechanism of O–H bond activation of alcohols by the uranium-substituted thiomolybdate cluster.
Understanding how modification of molecular structures changes the thermochemistry of H atom uptake can provide design criteria for the formation of highly active catalysts for reductive transformations. Herein, we describe the effect of doping an atomically precise polyoxotungstate with vanadium on proton-coupled electron transfer (PCET) reactivity. The Lindqvist-type polyoxotungstate [W 6 O 19 ] 2– displays reversible redox chemistry, which was found to be unchanged in the presence of acid, indicating an inability to couple reduction with protonation. However, the incorporation of a single vanadium center into the structure significantly changes the reactivity, and the potential required for one-electron reduction of [VW 5 O 19 ] 3– was shown to vary with the strength of the acid added. Construction of a potential-pK a diagram allowed assessment of the thermodynamics of H atom uptake, indicating BDFE(O–H) ≈ 64 kcal/mol, while chemical synthesis of the reduced/protonated derivative (TBA) 3 [VW 5 O 19 H] was used to probe the position of protonation.
The synthesis of a Np(IV) polyoxomolybdate– alkoxide sandwich complex, (TBA) 2 [Np{Mo 5 O 13 (OMe) 4 NO} 2 ] (TBA = tetrabutylammonium), is reported. This compound represents a rare example of a neptunium polyoxometalate cluster isolated outside of water, allowing for characterization of its electrochemical properties in nonaqueous solvents. Complexation of An(IV) cations fine-tunes the redox properties of the cluster, with the observed four reversible reductive events varying slightly both in potential and peak separation depending on the actinide present. The new Np(IV) complex also shows an irreversible event assigned to oxidation of Np(IV) to Np(V). New methodology for facile 17 O enrichment of (TBA) 2 [Mo 5 O 13 (OMe) 4 NO][Na(MeOH)] is presented, which provides a simple pathway to 17 O enriched analogues of the sandwich complexes discussed (Zr(IV), Hf(IV), Th(IV), U(IV), U(V), Np(IV)). 17 O NMR spectroscopy subsequently provides insights into both the nature of metal–oxygen bonding, as well as the influence of unpaired f-electrons on the local environment of the oxygen nuclei.
Combining a molecular thiomolybdate cluster, [Mo 3 S 13 ] 2− , with cadmium selenide quantum dots capped with amphiphilic ligands results in a highly active photocatalytic system for the production of hydrogen under visible light irradiation.
Actinide doping enhances redox chemistry of polyoxomolybdate-alkoxide clusters; the first isolable U( v ) polyoxometalate cluster is reported.
Single atoms of uranium supported on molybdenum sulfide surfaces (U@MoS 2 ) have been recently demonstrated to facilitate the hydrogen evolution reaction (HER) through electrocatalysis. Theoretical calculations have predicted uranium hydroxide moieties bound to edge-sulfur atoms of MoS 2 as a proposed transition state involved in the HER process. However, the isolation of relevant intermediates involved in this process remains a challenge, rendering mechanistic hypotheses unverified. The present work describes the isolation and characterization of a uranium-hydroxide intermediate on molybdenum sulfide surfaces using [(Cp* 3 Mo 3 S 4 )UCp*], a molecular model of a reduced uranium center supported at MoS 2 . Mechanistic investigations highlight the metalloligand cooperativity with uranium involved in the water activation pathway. The corresponding uranium-oxo analogue, [(Cp* 3 Mo 3 S 4 )Cp*U(═O)], was also accessed from the hydroxide cluster via hydrogen atom transfer and from [(Cp* 3 Mo 3 S 4 )UCp*] through an alternative direct oxygen atom transfer. These results provide an atomistic perspective on the reactivity of low-valent uranium at molybdenum sulfide surfaces toward water, modeling key intermediates associated with the HER of U@MoS 2 catalysts.
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Redox mediators are attractive solutions for addressing the stringent kinetic stipulations required for efficient energy conversion processes. In this work, we compare the electrochemical properties of four vanadium complexes, namely [V(acac) 3 ], [V 6 O 7 (OMe) 12 ], [ n Bu 4 N] 3 [V 6 O 13 (TRIS NO2 ) 2 ], and [ n Bu 4 N] 5 [V 18 O 46 (NO 3 )] in non-aqueous solutions on glassy carbon electrodes. The goal of this study is to investigate the electron transfer kinetics and diffusivity of these compounds under identical experimental conditions to develop an understanding of structure-function relationships that dictate the physicochemical properties of vanadium oxide assemblies. Complex selection was dictated by two criteria – (1) nuclearity of the transition metal complexes (2) distribution of electron density in the native electronic configuration. In conclusion, our analyses establish that electronic communication between metal centers significantly impacts charge transfer kinetics of these vanadium-based compounds.
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A series of pyridine dipyrrolide actinide(IV) complexes, ( Mes PDP Ph )AnCl 2 (THF) and An( Mes PDP Ph ) 2 (An = U, Th, where ( Mes PDP Ph ) is the doubly deprotonated form of 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine), have been prepared. Characterization of all four complexes has been performed through a combination of solid- and solution-state methods, including elemental analysis, single crystal X-ray diffraction, and electronic absorption and nuclear magnetic resonance spectroscopies. Collectively, these data confirm the formation of the mono- and bis-ligated species. Time-dependent density functional theory has been performed on all four An(IV) complexes, providing insight into the nature of electronic transitions that are observed in the electronic absorption spectra of these compounds. Room temperature, solution-state luminescence of the actinide complexes is presented. Both Th(IV) derivatives exhibit strong photoluminescence; in contrast, the U(IV) species are nonemissive.
The preparation of an actinide substituted cubane cluster, (Cp* 3 Mo 3 S 4 )Cp*UI 2 , and its reduced derivatives are reported. Structural and spectroscopic investigations provide insight into the unique interactions between the actinide and its redox-active molybdenum sulphide metalloligand, serving as a model to study atomically-dispersed, low-valent actinide ions on MoS 2 surfaces. To probe the ability of the assembly to facilitate multielectron small molecule activation, the reactivity of the fully-reduced cluster, (Cp* 3 Mo 3 S 4 )Cp*U, with azobenzene was investigated. Addition of the substrate results in the formation of a cis-bis-imido cluster, (Cp* 3 Mo 3 S 4 )Cp*U(=NPh) 2 . Here, cooperative reactivity between the actinide and redox-active support facilitates the 4e − -reduction of substrate.
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Introduction of a surface defect on a POV-alkoxide imparts both structural and electronic alterations, resulting in “switchable” PCET regiochemistry. Such features provide insight into PCET reactivity at metal oxide surfaces.
Reductive silylation of the uranyl dication with 1,4-bis(trimethylsilyl)dihydropyrazine, or “Mashima's reagent”, is detailed. The reagent simultaneously delivers silylium ions and electrons to multiple uranyl complexes, i.e. a pyridine dipyrrolide uranyl complex and a common uranyl-containing starting material, UO 2 Cl 2 (OPPh 3 ) 2 . This reaction results in quantitative activation of thermodynamically robust U=O bonds. Furthermore, the reductive functionalization of environmentally persistent actinyl species with Mashima's reagent is seen as a promising solution for nuclear waste remediation.