120 research outputs found
Accelerating slow excited state proton transfer
Visible light excitation of the ligand-bridged assembly [(bpy)2RuaII(L)RubII(bpy)(OH2)4+] (bpy is 2,2âČ-bipyridine; L is the bridging ligand, 4-phen-tpy) results in emission from the lowest energy, bridge-based metal-to-ligand charge transfer excited state (Lââą)RubIII-OH2 with an excited-state lifetime of 13 ± 1 ns. Nearâdiffusion-controlled quenching of the emission occurs with added HPO42â and partial quenching by added acetate anion (OAcâ) in buffered solutions with pH control. A SternâVolmer analysis of quenching by OAcâ gave a quenching rate constant of kq = 4.1 Ă 108 Mâ1â
sâ1 and an estimated pKa* value of âŒ5 ± 1 for the [(bpy)2RuaII(Lâąâ)RubIII(bpy)(OH2)4+]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)2RuaII(L)RubII(bpy)(OH)3+] in a H2PO4â/HPO42â buffer, back proton transfer occurs from H2PO4â to give [(bpy)2RuaII(L)Rub(bpy)(OH2)4+] with kPT,2 = 4.4 Ă 108 Mâ1â
sâ1. From the intercept of a plot of kobs vs. [H2PO4â], k = 2.1 Ă 106 sâ1 for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pKa values intermediate between pKa(H3O+) = â1.74 and pKa(H2O) = 15.7
Solar water splitting in a molecular photoelectrochemical cell
Solar water splitting into H2 and O2 with visible light has been achieved by a molecular assembly. The dye sensitized photoelectrosynthesis cell configuration combined with coreâshell structures with a thin layer of TiO2 on transparent, nanostructured transparent conducting oxides (TCO), with the outer TiO2 shell formed by atomic layer deposition. In this configuration, excitation and injection occur rapidly and efficiently with the injected electrons collected by the nanostructured TCO on the nanosecond timescale where they are collected by the planar conductive electrode and transmitted to the cathode for H2 production. This allows multiple oxidative equivalents to accumulate at a remote catalyst where water oxidation catalysis occurs
Water-Soluble Mo3S4 Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions
The [Mo3S4Cl3(dhprpe)3]+ (1+) cluster cation has been prepared by reaction between Mo3S4Cl4(PPh3)3 (solvent)2 and the watersoluble 1,2-bis(bis(hydroxypropyl)phosphino)ethane (dhprpe, L) ligand. The crystal structure of [1]2[Mo6Cl14] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure
with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo3S4(dhprpe-H)3]+ (2+). A detailed study based on stopped-flow, 31P{1H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acidâbase equilibria and the kinetics of interconversion between the 1+ and the 2+ forms. Both conversion of 1+ to 2+ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride
Electron transfer dynamics in semiconductorâchromophoreâpolyoxometalate catalyst photoanodes
Selectivity and Mechanism of Hydrogen Atom Transfer by an Isolable Imidoiron(III) Complex
This article discusses a mechanistic study of hydrogen atom transfer by an isolable iron (III) imido complex, LáŽčá”FeNAd (LáŽčá” = bulky ÎČ-diketiminate ligand, 2,4-bis(2,6-diisopropylphenylimido)pentyl; Ad = 1-adamantyl)
Tuning Reactivity and Electronic Properties through Ligand Reorganization within a Cerium Heterobimetallic Framework
Proton-Coupled Electron Transfer from Nitrogen. A NâH/NâD Kinetic Isotope Effect of 41.4
oAzophenylboronic Acid-Based Colorimetric Sensors for dFructose: oAzophenylboronic Acids with Inserted Protic Solvent Are the Key Species for a Large Color Change
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