Thermally Induced Oxygen Vacancies in BiOCl Nanosheets and Their Impact on Photoelectrochemical Performance**

Oxygen vacancies (OVs) have been reported to significantly alter the photocatalytic properties of BiOCl nanosheets. However, their formation mechanism and their role in the enhancement of photoelectrochemical performance remain unclear. In this work, thermally induced oxygen vacancies are introduced in BiOCl nanosheets by annealing in He atmosphere at various temperatures and their formation mechanism is investigated by in‐situ diffuse reflectance infrared (DRIFTS) measurements. The influence of OVs on band offset, carrier concentrations and photoelectrochemical performance are systematically studied. The results show that (1) the surface of BiOCl nanosheets is extremely sensitive to temperature and defects are formed at temperatures as low as 200 °C in inert atmosphere. (2) The formation of surface and bulk OVs in BiOCl is identified by a combination of XPS, in‐situ DRIFTS, and EPR experiments. (3) The photocurrent of BiOCl is limited by the concentration of charge carriers and shallow defect states induced by bulk oxygen vacancies, while the modulation of these parameters can effectively increase light absorption and carrier concentration leading to an enhancement of photoelectrochemical performance of BiOCl

Pinpointing the active species of the Cu(DAT) catalyzed oxygen reduction reaction

Dinuclear CuII complexes bearing two 3,5-diamino-1,2,4-triazole (DAT) ligands have gained considerable attention as a potential model system for laccase due to their low overpotential for the oxygen reduction reaction (ORR). In this study, the active species for the ORR was investigated. The water soluble dinuclear copper complex (Cu(DAT)) was obtained by mixing a 1 : 1 ratio of Cu(OTf)2 and DAT in water. The electron paramagnetic resonance (EPR) spectrum of Cu(DAT) showed a broad axial signal with a g factor of 2.16 as well as a low intensity Ms = ±2 absorption characteristic of the Cu2(μ-DAT)2 moiety. Monitoring the typical 380 nm peak with UV-Vis spectroscopy revealed that the Cu2(μ-DAT)2 core is extremely sensitive to changes in pH, copper to ligand ratios and the presence of anions. Electrochemical quartz crystal microbalance experiments displayed a large decrease in frequency below 0.5 V versus the reversible hydrogen electrode (RHE) in a Cu(DAT) solution implying the formation of deposition. Rotating ring disk electrode experiments showed that this deposition is an active ORR catalyst which reduces O2 all the way to water at pH 5. The activity increased significantly in the course of time. X-ray photoelectron spectroscopy was utilized to analyze the composition of the deposition. Significant shifts in the Cu 2p3/2 and N 1s spectra were observed with respect to Cu(DAT). After ORR catalysis at pH 5, mostly CuI and/or Cu0 species are present and the deposition corresponds to previously reported electrodepositions of copper. This leads us to conclude that the active species is of a heterogeneous nature and lacks any structural similarity with laccase

Molybdenum Triamidoamine Systems. Reactions Involving Dihydrogen Relevant to Catalytic Reduction of Dinitrogen

[HIPTN[subscript 3]N]Mo(N[subscript 2]) (MoN[subscript 2]) ([HIPTN[subscript 3]N][superscript 3−] = [(HIPTNCH2CH2)3N]3− where HIPT = 3,5-(2,4,6-i-Pr[subscript 3]C[subscript 6]H[subscript 2])[subscript 2]C[subscript 6]H[subscript 3]) reacts with dihydrogen slowly (days) at 22 °C to yield [HIPTN[subscript 3]N]MoH[subscript 2] (MoH[subscript 2]), a compound whose properties are most consistent with it being a dihydrogen complex of Mo(III). The intermediate in the slow reaction between MoN[subscript 2] and H[subscript 2] is proposed to be [HIPTN[subscript 3]N]Mo (Mo). In contrast, MoN[subscript 2], MoNH[subscript 3], and MoH[subscript 2] are interconverted rapidly in the presence of H[subscript 2], N[subscript 2], and NH[subscript 3], and MoH[subscript 2] is the lowest energy of the three Mo compounds. Catalytic runs with MoH[subscript 2] as a catalyst suggest that it is competent for reduction of N[subscript 2] with protons and electrons under standard conditions. [HIPTN[subscript 3]N]MoH[subscript 2] reacts rapidly with HD to yield a mixture of [HIPTN[subscript 3]N]MoH[subscript 2], [HIPTN[subscript 3]N]MoD[subscript 2], and [HIPTN[subscript 3]N]MoHD, and rapidly catalyzes H/D exchange between H[subscript 2] and D[subscript 2]. MoH[subscript 2] reacts readily with ethylene, PMe[subscript 3], and CO to yield monoadducts. Reduction of dinitrogen to ammonia in the presence of 32 equiv of added hydrogen (vs Mo) is not catalytic, consistent with dihydrogen being an inhibitor of dinitrogen reduction.National Institutes of Health (U.S.) (GM 31978

Pinpointing the active species of the Cu(DAT) catalyzed oxygen reduction reaction

\u3cp\u3eDinuclear Cu\u3csup\u3eII\u3c/sup\u3e complexes bearing two 3,5-diamino-1,2,4-triazole (DAT) ligands have gained considerable attention as a potential model system for laccase due to their low overpotential for the oxygen reduction reaction (ORR). In this study, the active species for the ORR was investigated. The water soluble dinuclear copper complex (Cu(DAT)) was obtained by mixing a 1 : 1 ratio of Cu(OTf)\u3csub\u3e2\u3c/sub\u3e and DAT in water. The electron paramagnetic resonance (EPR) spectrum of Cu(DAT) showed a broad axial signal with a g factor of 2.16 as well as a low intensity M\u3csub\u3es\u3c/sub\u3e = ±2 absorption characteristic of the Cu\u3csub\u3e2\u3c/sub\u3e(μ-DAT)\u3csub\u3e2\u3c/sub\u3e moiety. Monitoring the typical 380 nm peak with UV-Vis spectroscopy revealed that the Cu\u3csub\u3e2\u3c/sub\u3e(μ-DAT)\u3csub\u3e2\u3c/sub\u3e core is extremely sensitive to changes in pH, copper to ligand ratios and the presence of anions. Electrochemical quartz crystal microbalance experiments displayed a large decrease in frequency below 0.5 V versus the reversible hydrogen electrode (RHE) in a Cu(DAT) solution implying the formation of deposition. Rotating ring disk electrode experiments showed that this deposition is an active ORR catalyst which reduces O\u3csub\u3e2\u3c/sub\u3e all the way to water at pH 5. The activity increased significantly in the course of time. X-ray photoelectron spectroscopy was utilized to analyze the composition of the deposition. Significant shifts in the Cu 2p\u3csub\u3e3/2\u3c/sub\u3e and N 1s spectra were observed with respect to Cu(DAT). After ORR catalysis at pH 5, mostly Cu\u3csup\u3eI\u3c/sup\u3e and/or Cu\u3csup\u3e0\u3c/sup\u3e species are present and the deposition corresponds to previously reported electrodepositions of copper. This leads us to conclude that the active species is of a heterogeneous nature and lacks any structural similarity with laccase.\u3c/p\u3

The electronic structure of (diiminopyridine)cobalt(I) complexes

DFT calculations show that square-planar (LCoR)-R-I complexes of a diiminopyridine ligand are best regarded as containing low-spin Co-II antiferromagnetically coupled to a ligand radical anion. The lowest triplet state, corresponding to a 3d(z)(2)-->pi* excitation, is calculated to be only a few kcal/mol above the ground state, and is thermally accessible. The anomalous H-1 NMR chemical shifts of the LCoR complexes are suggested to be due to thermal population of the triplet state at room temperature. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004

Binuclear [(cod)(Cl)Ir(bpi)Ir(cod)]+ for Catalytic Water Oxidation

The binuclear iridium complex [(cod)(Cl)Ir(bpi)Ir(cod)]PF6 (bpi = (pyridin-2-ylmethyl)(pyridin-2-ylmethylene)amine; cod = 1,5-cyclooctadiene) reveals a noteworthy asymmetric binuclear coordination geometry, wherein the bpi ligand acts as a heteroditopic ligand and has an unusual π-coordinated imine moiety. This species is an effective precatalyst for water oxidation. After a short incubation time the catalyst reveals a turnover frequency of 3400 mol mol-1 s-1 with an overall turnover number >1000. © 2011 American Chemical Society.Financial support from the European Research Council (ERC Grant Agreement 202886-CatCIR), NWO-CW (VIDI grant 700.55.426, VENI grant 700.59.410), the MEC/FEDER (Project CTQ2008-03860, Spain), and the University of Amsterdam is gratefully acknowledged.Peer Reviewe

A Selective Copper Based Oxygen Reduction Catalyst for the Electrochemical Synthesis of H 2 O 2 at Neutral pH

H2O2 is a bulk chemical used as "green" alternative in a variety of applications, but has an energy and waste intensive production method. The electrochemical O2 reduction to H2O2 is viable alternative with examples of the direct production of up to 20% H2O2 solutions. In that respect, we found that the dinuclear complex Cu2(btmpa) (6,6'-bis[[bis(2-pyridylmethyl)amino]methyl]-2,2'-bipyridine) reduces O2 to H2O2 with a selectivity up to 90 % according to single linear sweep rotating ring disk electrode measurements. Microbalance experiments showed that complex reduction leads to surface adsorption thereby increasing the catalytic current. More importantly, we kept a high Faradaic efficiency for H2O2 between 60 and 70 % over the course of 2 h of amperometry by introducing high potential intervals to strip deposited copper (depCu). This is the first example of extensive studies into the long term electrochemical O2 to H2O2 reduction by a molecular complex which allowed to retain the high intrinsic selectivity of Cu2(btmpa) towards H2O2 production leading to relevant levels of H2O2

Elucidation of the structure of a thiol functionalized Cu-tmpa complex anchored to gold via a self-assembled monolayer

The structure of the copper complex of the 6-((1-butanethiol)oxy)-tris(2-pyridylmethyl)amine ligand (Cu-tmpa-O(CH2)4SH) anchored to a gold surface has been investigated. To enable covalent attachment of the complex to the gold surface, a heteromolecular self-assembled monolayer (SAM) of butanethiol and a thiol-substituted tmpa ligand was used. Subsequent formation of the immobilized copper complex by cyclic voltammetry in the presence of Cu(OTf)2 resulted in the formation of the anchored Cu-tmpa-O(CH2)4SH system which, according to scanning electron microscopy and X-ray diffraction, did not contain any accumulated copper nanoparticles or crystalline copper material. Electrochemical investigation of the heterogenized system barely showed any redox activity and lacked the typical CuII/I redox couple in contrast to the homogeneous complex in solution. The difference between the heterogenized system and the homogeneous complex was confirmed by X-ray photoelectron spectroscopy; the XPS spectrum did not show any satellite features of a CuII species but instead showed the presence of a CuI ion in a 2:3 ratio to nitrogen and a 2:7 ratio to sulfur. The +I oxidation state of the copper species was confirmed by the edge position in the X-ray absorption near-edge structure (XANES) region of the X-ray absorption spectrum. These results show that upon immobilization of Cu-tmpa-O(CH2)4SH, the resulting structure is not identical to the homogeneous CuII-tmpa complex. Upon anchoring, a novel CuI species is formed instead. This illustrates the importance of a thorough characterization of heterogenized molecular systems before drawing any conclusions regarding the structure-function relationships

Cooperative double deprotonation of bis(2-picolyl)amine leading to unexpected bimetallic mixed valence (M-I, MI) rhodium and iridium complexes

Cooperative reductive double deprotonation of the complex [Rh I(bpa)(cod)]+ ([4]+, bpa = PyCH 2NHCH2Py) with one molar equivalent of base produces the bimetallic species [(cod)Rh(bpa-2H)Rh(cod)] (7), which displays a large Rh -I,RhI contribution to its electronic structure. The doubly deprotonated ligand in 7 hosts the two >Rh(cod)> fragments in two distinct compartments: a >square planar compartment> consisting of one of the Py donors and the central nitrogen donor and a >tetrahedral Ï€-imine compartment> consisting of the other pyridine and an >imine C=N> donor. The formation of an >imine donor> in this process is the result of substantial electron transfer from the {bpa-2H}2- ligand to one of the rhodium centers to form the neutral imine ligand bpi (bpi = PyCH2N=CHPy). Hence, deprotonation of [RhI(bpa)(cod)] + represents a reductive process, effectively leading to a reduction of the metal oxidation state from RhI to Rh-I. The dinuclear iridium counterpart, complex 8, can also be prepared, but it is unstable in the presence of 1 mol equiv of the free bpa ligand, leading to quantitative formation of the neutral amido mononuclear compound [Ir I(bpa-H)(cod)] (2). All attempts to prepare the rhodium analog of 2 failed and led to the spontaneous formation of 7. The thermodynamic differences are readily explained by a lower stability of the M-I oxidation state for iridium as compared to rhodium. The observed reductive double deprotonation leads to the formation of unusual structures and unexpected reactivity, which underlines the general importance of >redox noninnocent ligands> and their substantial effect on the electronic structure of transition metals. © 2011 American Chemical Society.This research was supported by the MICINN/FEDER (Project CTQ2008-03860, Spain) and Gobierno de Aragón (GA, Project PI55/08, Spain), The Netherlands Organization for Scientific Research (NWO_CW VIDI project 700.55.426), the European Research Council (ERC, EU seventh framework program, grant agreement 202886-CatCIR), and the University of Amsterdam. M.P.d.R. and L.A. thank GA and MICINN/FEDER, respectively, for a fellowship.Peer Reviewe