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

Stoichiometric reduction reactions of two metal-organic frameworks (MOFs) by the solution reagents (M = Cr, Co) are described. The two MOFs contain clusters with TiO rings: TiO(OH)(bdc); bdc = terephthalate (MIL-125) and TiO(OH)(bdc-NH); bdc-NH = 2-aminoterephthalate (NH-MIL-125). The stoichiometry of the redox reactions was probed using solution NMR methods.

Cation Effects on the Reduction of Colloidal ZnO Nanocrystals.

The effects of a variety of monatomic cations (H, Li, Na, K, Mg, and Ca) and larger cations (decamethylcobaltocenium and tetrabutylammonium) on the reduction of colloidal ZnO nanocrystals (NCs) are described. Suspensions of "TOPO"-capped ZnO NCs in toluene/THF were treated with controlled amounts of one-electron reductants (CoCp* or sodium benzophenone anion radical) and cations. Equilibria were quickly established and the extent of NC reduction was quantified via observation of the characteristic near-IR absorbance of conduction band electrons.

Proton-Controlled Reduction of ZnO Nanocrystals: Effects of Molecular Reductants, Cations, and Thermodynamic Limitations.

Charge carriers (electrons) were added to ZnO nanocrystals (NCs) using the molecular reductants CoCp*2 and CrCp*2 [Cp* = η(5)-pentamethylcyclopentadienyl]. The driving force for electron transfer from the reductant to the NCs was varied systematically by the addition of acid, which lowers the energy of the NC orbitals. In the presence of excess reductant, the number of electrons per NC (⟨ne(-)⟩) reaches a maximum, beyond which the addition of more acid has no effect.

Low capping group surface density on zinc oxide nanocrystals.

The ligand shell of colloidal nanocrystals can dramatically affect their stability and reaction chemistry. We present a methodology to quantify the dodecylamine (DDA) capping shell of colloidal zinc oxide nanocrystals in a nonpolar solvent. Using NMR spectroscopy, three different binding regimes are observed: strongly bound, weakly associated, and free in solution.

Effect of protons on the redox chemistry of colloidal zinc oxide nanocrystals.

Electron transfer (ET) reactions of colloidal 3-5 nm diameter ZnO nanocrystals (NCs) with molecular reagents are explored in aprotic solvents. Addition of an excess of the one-electron reductant Cp*2Co (Cp* = pentamethylcyclopentadienyl) gives NCs that are reduced by up to 1-3 electrons per NC. Protons can be added stoichiometrically to the NCs by either a photoreduction/oxidation sequence or by addition of acid.

Catalytic hydrogen evolution from a covalently linked dicobaloxime.

A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at -0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions.

Titanium and zinc oxide nanoparticles are proton-coupled electron transfer agents.

Oxidation/reduction reactions at metal oxide surfaces are important to emerging solar energy conversion processes, photocatalysis, and geochemical transformations. Here we show that the usual description of these reactions as electron transfers is incomplete. Reduced TiO(2) and ZnO nanoparticles in solution can transfer an electron and a proton to phenoxyl and nitroxyl radicals, indicating that e(-) and H(+) are coupled in this interfacial reaction.