Pendant Oxygen Research Articles

Tuning of lattice oxygen reactivity and scaling relation to construct better oxygen evolution electrocatalyst

Developing efficient and low-cost electrocatalysts for oxygen evolution reaction is crucial in realizing practical energy systems for sustainable fuel production and energy storage from renewable energy sources. However, the inherent linear scaling relation for most catalytic materials imposes a theoretical overpotential ceiling, limiting the development of efficient electrocatalysts. Herein, using modeled NaxMn3O7 materials, we report an effective strategy to construct better oxygen evolution electrocatalyst through tuning both lattice oxygen reactivity and scaling relation via alkali metal ion mediation. Specifically, the number of Na+ is linked with lattice oxygen reactivity, which is determined by the number of oxygen hole in oxygen lone-pair states formed by native Mn vacancies, governing the barrier symmetry between O–H bond cleavage and O–O bond formation. On the other hand, the presence of Na+ could have specific noncovalent interaction with pendant oxygen in *OOH to overcome the limitation from linear scaling relation, reducing the overpotential ceiling. Combining in situ spectroscopy-based characterization with first-principles calculations, we demonstrate that an intermediate level of Na+ mediation (NaMn3O7) exhibits the optimum oxygen evolution activity. This work provides a new rational recipe to develop highly efficient catalyst towards water oxidation or other oxidative reactions through tuning lattice oxygen reactivity and scaling relation.

A Study of the Reichardt $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ Parameter using Solvent Molecular Properties Derived from Computation Chemistry and Consideration of the Kamlet and Taft α Scale of Solvent Hydrogen Bond Donor Acidities

Reichardt’s normalized $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ parameter for solvent polarity has been analyzed in terms of properties of solvent molecules estimated from quantum–mechanical calculations of isolated solvent molecules. The analyses show that $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ has a strong dependence on the partial charge on the most positive hydrogen atom in the solvent molecule, reflecting hydrogen bonding at the pendant oxygen atom of the betaine dye used to define the ET(30) scale. There are smaller, and roughly equal, dependences on the dipole moments and quadrupolar amplitudes of the solvent molecules and an inverse dependence on the solvent polarizability. These three dependences reflect the solvent polarity, that is, the ability to stabilize charge through longer-range interactions. The reason for the inverse dependence on the solvent polarizability is unclear, but a similar dependence was found previously in the analysis of the Kamlet, Abboud and Taft π* scale. The resulting equation for $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ reproduces the experimental values for around 160 solvents, representing most classes of organic solvents, with a standard deviation of around 0.07 { $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ values range from 0 to 1}. The Kamlet and Taft α scale of hydrogen bond donor acidities, which is, in effect, derived from the differences between the $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ and π* values for a solvent, is discussed. The results of the present analyses of $$E_{{\text{T}}}^{{\text{N}}} \left( {30} \right)$$ and earlier analyses of π* indicate that, while the α values capture the effect of solvent hydrogen bond donor acidity, it also contains residual dependences on other molecular properties. These residual dependences result from the differences in the dependences of the $$E_{{\text{T}}}^{{\text{N}}} \left({30} \right)$$ and π* on solvent properties.

Mechanistic insights into catalytic CO2 hydrogenation using Mn(i)-complexes with pendant oxygen ligands

Hydrogenation of CO2 to formic acid catalysed by Mn(i)-complexes with pendant oxygen ligands.

Critical Role of Pendant Group Substitution on the Performance of Efficient All-Polymer Solar Cells

Most high-performance all-polymer solar cell systems employ donor polymers with side groups containing bulky aromatic units. The rationale behind the use of bulky side groups in efficient all-polymer systems, however, is not well-understood. In this study, we investigate the doubling of power conversion efficiency in all-polymer solar cells that occurs when substituting the pendant oxygen group in polymer donor PTB7 for thiophene. Specifically, polymer blends using either PTB7 or PTB7-Th as donor with P(NDI2OD-T2) as acceptor are compared. We comprehensively examine the photophysics, morphology, and device physics of these two systems and find that PTB7-Th:P(NDI2OD-T2) blends have suppressed geminate recombination and improved charge collection efficiencies compared to PTB7:P(NDI2OD-T2) blends. While the switching of oxygen for thiophene does not have a dramatic effect on blend morphology, the bulky side group in PTB7-Th helps to destabilize the interfacial charge transfer state, with 5-fold higher hole m...

Thiolate-Bridged Nickel–Iron and Nickel–Ruthenium Complexes Relevant to the CO-Inhibited State of [NiFe]-Hydrogenase

By employing S(CH2CH2S–)2 (tpdt) and O(CH2CH2S–)2 (opdt) as bridging ligands, two nickel–iron and two nickel–ruthenium heterodimetallic complexes, [Cp*M(μ-1κ3SSS′:2κ2SS-tpdt)Ni(dppe)][PF6] (1, M = Fe; 3, M = Ru) and [Cp*M(μ-1κ3SSO:2κ2SS-opdt)Ni(dppe)][PF6] (2, M = Fe; 4, M = Ru) (Cp* = η5-C5Me5; dppe = Ph2P(CH2)2PPh2), were obtained by a one-pot synthetic method and were identified by spectroscopy and X-ray crystallography. At 1 atm of CO, the pendant oxygen atom dissociated from the iron or ruthenium center and rapidly transferred to the nickel center when a CO molecule attacked the iron or ruthenium center in 2 and 4. However, there was no similar reaction occurring in 1 and 3 with the pendant sulfur atom. We confirmed the solid-state structure of the CO complex [Cp*Fe(t-CO)(μ-1κ2SS:2κ3SSO-opdt)Ni(dppe)][PF6] (5), which represents a possible configuration in the CO-inhibited state of [NiFe]-hydrogenase and exhibits no catalytic activity in electrochemical proton reduction.

Structural features of a series of S-alkylated and non-S-alkylated aminothiolate nickel(II) complexes

The structural aspects of a family of S-alkylated complexes, generated by reacting iodoacetamide or iodoethanol with two mononuclear Ni(II) diaminodithiolate complexes are discussed. The S-alkylation reactions were investigated with particular attention paid to the size of the chelate ring that straps the N,N′-methylamine donors. In one complex the N-methyl groups are cis to each other and in the other they are trans. Both complexes undergo S-alkylation with two equivalents of either reagent, that coordinates through the pendant oxygen to the Ni(II), forming dications with an N2S2O2 ligand donor set. Crystal structures of [NiC12H26N4O2S2]I2 · MeOH, [NiC12H28N2O2S2]I2, and [NiC13H30N2O2S2]I2 · 1/2MeOH, are determined by single crystal X-ray analysis. The N-methyl groups in each of the alkylated derivatives are trans to each other, suggesting that the cis configuration is highly unfavored for such complexes in octahedral conformation. Crystal packing data shows that each of the alkylated complexes interacts closely with the iodide counterions, and with solvent if present; some of these interactions include H-bonds. Only the iodoacetamide derivative shows any significant interaction with a neighboring molecule.

Three-Dimensional Metal–Organic Framework with Highly Polar Pore Surface: H2 and CO2 Storage Characteristics

A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) (1), (bipy =4,4'-bipyridine and Himdc = 4,5-imidazoledicarboxylate) has been synthesized and structurally characterized. The highly rigid and stable framework contains a 3D channel structure with highly polar pore surfaces decorated with pendant oxygen atoms of the Himdc linkers. The desolvated framework [Cd(bipy)(0.5)(Himdc)](n) (1') is found to exhibit permanent porosity with high H(2) and CO(2) storage capacities. Two H(2) molecules occluded per unit formula of 1' and the corresponding heat of H(2) adsorption (ΔH(H2)) is about ∼9.0 kJ/mol. The high value of ΔH(H2) stems from the preferential electrostatic interaction of H(2) with the pendent oxygen atoms of Himdc and aromatic bipy linkers as determined from first-principles density functional theory (DFT) based calculations. Similarly, DFT studies indicate CO(2) to preferentially interact electrostatically (C(δ+)···O(δ-)) with the uncoordinated pendent oxygen of Himdc. It also interacts with bipy through C-H···O bonding, thus rationalizing the high heat (ΔH(CO2) ∼ 35.4 kJ/mol) of CO(2) uptake. Our work unveiled that better H(2) or CO(2) storage materials can be developed through the immobilization of reactive hetero atoms (O, N) at the pore surfaces in a metal-organic framework.

Oligomerization of ethylene using tridentate nickel catalysts bearing ether-pyrazol ligands with pendant O- and S-donor groups

Abstract A series of tridentate pyrazol ligands with pendant O- and S-donor groups (L1-L5) and their corresponding nickel(II) chloride complexes (1–5) were synthesized and fully characterized. All nickel precatalysts, activated with methylaluminoxane (MAO), exhibited high activities for ethylene oligomerization [TOF = 17.1–75.8 × 10 3 mol(ethylene)(mol(Ni)) − 1 h − 1 )] with good selectivities for 1-butene produced (62.9 – 81.3%). The catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-donor groups, and the substituents on the phenol group. Activation of nickel precatalyst 1 with ethylaluminum sesquichloride (Et 3 Al 2 Cl 3 , EASC) instead of MAO produced a significantly better catalyst system than 1/MAO (TOF = 227,000 vs. 30,900 (mol C 2 H 4 )⋅(mol Ni − 1 h − 1 ); however, the 1-butene selectivity was drastically reduced, attaining only 28% with a concomitant production of larger amounts of internal butenes (51.4%) and hexenes (28.2%). Under optimized conditions ([Ni] = 10μmol, 30°C, oligomerization time = 20 min, 40 bar ethylene, [Al]/[Ni] = 250), precatalyst 1 led to TOF = 75,800 (mol C 2 H 4 )⋅(mol Ni − 1 h − 1 ) and 76.1% selectivity for 1-butene.

Myo-Inositol oxygenase: a radical new pathway for O(2) and C-H activation at a nonheme diiron cluster.

The enzyme myo-inositol oxygenase (MIOX) catalyzes conversion of myo-inositol (cyclohexan-1,2,3,5/4,6-hexa-ol or MI) to d-glucuronate (DG), initiating the only known pathway in humans for catabolism of the carbon skeleton of cell-signaling inositol (poly)phosphates and phosphoinositides. Recent kinetic, spectroscopic and crystallographic studies have shown that the enzyme activates its substrates, MI and O(2), at a carboxylate-bridged nonheme diiron(ii/iii) cluster, making it the first of many known nonheme diiron oxygenases to employ the mixed-valent form of its cofactor. Evidence suggests that: (1) the Fe(iii) site coordinates MI via its C1 and C6 hydroxyl groups; (2) the Fe(ii) site reversibly coordinates O(2) to produce a superoxo-diiron(iii/iii) intermediate; and (3) the pendant oxygen atom of the superoxide ligand abstracts hydrogen from C1 to initiate the unique C-C-bond-cleaving, four-electron oxidation reaction. This review recounts the studies leading to the recognition of the novel cofactor requirement and catalytic mechanism of MIOX and forecasts how remaining gaps in our understanding might be filled by additional experiments.

A catalytic asymmetric method for the synthesis of gamma-unsaturated beta-amino acid derivatives.

Catalytic enantioselective synthesis of beta-amino acid derivatives is an area of intense interest, due to the importance of these compounds as components in pharmaceutical agents and peptidomimetics. In this report, we present the first catalytic enantioselective method for the synthesis of gamma-unsaturated beta-amino acids and their corresponding 1,3-amino alcohol derivatives. This methodology takes advantage of a highly enantioselective vinylzinc addition to an aldehyde to set chirality. The resulting allylic alcohols are then transformed into the corresponding allylic amines via Overman's [3,3]-sigmatropic imidate rearrangement, and subsequent one-pot deprotection-oxidation of a pendant oxygen leads to the gamma-unsaturated beta-amino acid derivatives of high enantiopurity.

Novel, Efficient, Palladium-Based System for the Polymerization of Norbornene Derivatives: Scope and Mechanism

[(1,5-Cyclooctadiene)(CH3)Pd(Cl)], when reacted in situ with 1 equiv of a monodentate phosphine ligand and 1 equiv of the complex Na+[3,5-(CF3)2C6H3]4B- was found to catalyze the vinyl addition polymerization of norbornene derivatives, including those with pendant oxygen functionalities. For norbornene, a polymerization rate of 1000 tons norbornene/mol Pd·h was observed at 25 °C. For several norbornene derivatives, the molecular weight of the polymer was found to decrease with increasing amounts of added 2-propanol. Mechanistic data confirm a vinyl insertion mechanism for these polymerizations. The polymerization rate was found to decrease dramatically for norbornene derivatives with pendant oxygen functionalities. The effect of coordinating solvents and the uptake of endo vs exo isomers for functionalized norbornenes was tested. Experiments show that (a) the endo isomer reacts more slowly than the exo isomer and (b) both isomers react much more slowly compared to norbornene derivatives lacking coordinati...

ChemInform Abstract: Photochemical Reactions in the Interior of a Zeolite. Part 5. The Origin of the Zeolite Induced Regioselectivity in the Singlet Oxygen Ene Reaction.

Abstract Photooxidations of several new alkenes in the interior of methylene blue doped NaY are reported. The results suggest that the novel regiochemistry of these reactions can be rationalized by invoking both cation complexation with the alkenes and electrostatic interaction between the cation and the pendant oxygen on the developing perepoxide.

Photochemical Reactions in the Interior of a Zeolite. Part 5: The Origin of the Zeolite Induced Regioselectivity in the Singlet Oxygen Ene Reaction

Photooxidations of several new alkenes in the interior of methylene blue doped NaY are reported. The results suggest that the novel regiochemistry of these reactions can be rationalized by invoking both cation complexation with the alkenes and electrostatic interaction between the cation and the pendant oxygen on the developing perepoxide.

Tailoring the optical properties of metal-oxide electrochromic mixtures

A semi-empirical approach is given to show how an optical-shift parameter S (ia the frequency maximum of an optical band) correlates with the composition of a mixture of electrochromic oxides such as tungsten trioxide, thereby allowing the colours of electrochromic oxide mixtures to be tailored. It is shown that changing the relative amounts of charge-donating oxygen-based moieties (oxide, pendant oxygen and bridging oxygen) in the mixture systematically varies the electrochromic colour according to ‘shifting constants’ σ, which depend on the identities of both dopant and host oxides.

Photooxidations in zeolites. Part 2: A new mechanistic model for reaction selectivity in singlet oxygen ene reactions in zeolitic media

Abstract The singlet oxygen ene reaction in Methylene Blue doped NaY was examined. A new mechanism is proposed which involves complexation of the sodium cation to the pendant oxygen in the perepoxide intermediate. It is argued that this complexation leads to greater positive charge on the carbon framework and to steric interactions between the sodium and the groups on the proximal side of the perepoxide.

Synthesis and X-ray structural characterization of cobalt(II), copper(II), and silver(I) complexes of triphenylphosphoniopropionate

Four transition-metal carboxylate-like complexes have been synthesized from the reaction of the tertiary phosphine betaine triphenylphosphoniopropionate, Ph3P+(CH2)2CO2−, with Co(ClO4)2· 6H2O, Cu(ClO4)2·6H2O, Cu(BF4)2·xH2O, and AgClO4, respectively, and fully characterized by single-crystal X-ray analysis. [CoPh3P(CH2)2CO24(H2O)2](ClO4)2·2H2O, 1, space groupP¯ l witha=9.195(2),b=13.000(2),c=18.795(3) A,α=102.52(1),β=90.12(1),γ=109.28(2)° andZ=1; [CuPh3P(CH2)2CO24][Cu2μ -Ph3P(CH2)2CO2 -O,O′4(H2O)2] (ClO4)6· 4H2O, 2, space groupP2l/c witha=14.225(3),b=24.624(6),c=24.297(5) A,β=94.18(1)°, andZ=2; [CuPh3,P(CH2)2CO2Me2N(CH2)2NMe2(H2O)2](BF4)2,3, space groupP2l/c witha=17.668(2),b=13.454(3),c=15.876(2) A,β=116.45(1)°, andZ=4; [Ag2Ph3P(CH2)2CO22(ClO4)]2(ClO4)2,4, space groupP¯ l witha=10.925(2),b=13.110(3),c=18.795(3) A,α=82.93(3),β=87.45(3),γ=67.49(3)°, andZ=2. In complex1, the cobalt(II) atom is located in an inversion center and coordinated by four unidentate betaine ligands and a pair oftrans aqua ligands, and strong hydrogen bonds are formed between the aqua ligands and the pendant oxygen atoms of the betaine ligands. In complex2, mononuclear and dinuclear cations coexist in the asymmetric unit. In the mixed-ligand complex3 the betaine ligand acts in the unidentate coordination mode andN,N,N′,N′-tetramethylethylenediamine (tmen) in the chelate mode. Complex4 contains a discrete centrosymmetric tetranuclear cations in which one pair of betaine ligands act in the bidentate bridging mode and the other in both bidentate and one-atom bridging modes.

Mononuclear cadmium(II) halide complexes of triphenylphosphoniobutyrate, [CdCl 2L 2-H 2O] and [CdX 2L 2] (X = Br, I)(L = Ph 3P + (CH 2) 3CO 2−)

Three mononuclear cadmium(II) complexes containing the tertiary phosphine betaine ligand triphenylphosphoniobutyrate, Ph 3P +(CH 2) 3CO 2 −, (L) have been synthesized and characterized by single crystal X-ray analysis. In CdCl 2L 2 · H 2O ( 1) the cadmium(II) atom is coordinated by pairs of unidentate betaine ligands and chloro ligands in a tetrahedral environment, and the primarily discrete species are joined by donor hydrogen bonds from the solvated water molecules to the pendant oxygen atom of the betaine ligands to form a dimer. In CdBr 2L 2 ( 2) the cadmium(II) atom is coordinated in a similar manner, but one CdBr distance is so long that it may be considered as a weak interaction. In CdI 2L 2 ( 3) the betaine ligands act differently in the bidentate chelate and unidentate modes.

Structure and stability of small titanium/oxygen clusters studied by ab initio quantum chemical calculations

Ab initio calcns. have been performed on TinO2n-δ clusters, with n = 1-3 and δ = 0, 1, as well as on some of their ionized species. The geometries of the different clusters were optimized and vibrational analyses were performed at the ground-state equil. geometries. The Ti-O bond lengths are essentially detd. by the coordination nos. of the resp. atoms, independent of n. The clusters are characterized by having any low pendant oxygen vibrational frequencies. The ionization energies for the (TiO2)n clusters were significantly higher than those of oxygen-deficient, TinO2n-1, clusters. Some anomalous features of the n = 1 cluster, TiO2, as compared to clusters with n > 1, are discussed. Recent exptl. mass spectrometric observations on titanium oxide clusters are discussed in the light of the present findings.

Structural chemistry of organotin carboxylates: II. The crystal structure of the dicarboxylato tetraorganodistannoxane:{sunBu 2Sn(O 2CC 5H 4N)] 2O} 2

The crystal structure determination of the compound {[ nBu 2Sn(2-pic)] 2O} 2 (2-pic = O 2CC 5H 4N) has revealed the presence of two distinct tin atom geometrics in the dicarboxylato tetraorganostannoxane structure. The centrosymmetric dimer also features two unique carboxylate groups, one of which bridges two tin centres via one oxygen atom only (the pendant oxygen atom is not coordinated to tin) and the other carboxylate functions essentially in the monodentate mode. One tin atom is six coordinate, and the other is seven coordinate by virtue of weak but significant intramolecular interactions. The two tin atom environments are best described as being based on distorted octahedral and pentagonal bipyramidal geometries, respectively. The 2-pyridinecarboxylate ligands introduce a major structural change in the dicarboxylato tetraorganostannoxane structure as a result of the formation of SnN bonds. In solution, 119Sn NMR spectroscopy indicates the presence of two distinct hexacoordinate tin centres. Crystals are orthorhombic with space group Pbca and unit cell dimensions a 15.760(2), b 18.208(3) and c 22.369(2) Å. The structure was refined by a full-matrix least-squares procedure to final R = 0.035 for 3665 reflections with I > - 2.5σ ( I).

Absorption and CD Spectral Properties of Bis(ethylenediamine)cobalt(III) Complexes with O-Bonded Sulfoxide and Seleninate

Abstract The absorption and CD spectral behavior of [Co{OS(CH3)CH2CH2NH2}(en)2]3+ and [Co{OSe(O)CH2CH2NH2}(en)2]2+ was discussed. The O-bonded seleninato isomer, Λ-(+)500CD-[Co{OSe(O)CH2CH2NH2}(en)2]2+, showed racemization at the chiral selenium atom in an aqueous solution and a shift of the equilibrium between the (R) and (S) configurations of the chiral selenium atom through the protonation on the pendant oxygen atom.