C-H Bond Activation by an Antimony(V) Oxo Intermediate Accessed through Electrochemical Oxidation of Antimony(III) Tetrakis(thiocyano)corrole.

A new class of antimony(III) corroles has been described. The photophysical properties of these newly synthesized tetrakis(thiocyano)corrolatoantimony(III) derivatives having four SCN groups on the bipyrrole unit of corrole are drastically altered compared to their ß-unsubstituted corrolatoantimony(III) analogues. The UV-vis and emission spectra of tetrakis(thiocyano)corrolatoantimony(III) derivatives are significantly red-shifted (roughly 30-40 nm) in comparison with their ß-unsubstituted corrolatoantimony(III) derivatives. The Q bands are significantly strengthened. The intensity of the most prominent Q band is roughly 70% that of the Soret band and absorbs strongly at the far-red region, i.e., at 700-720 nm. These molecules emit light in the near-infrared region (700-900 nm). Tetrakis(thiocyano)corrolatoantimony(III) undergoes electrochemical anodic oxidation to form SbV═O species, which facilitates electrocatalytic oxygen evolution reaction (OER) and the activation of benzylic C-H to produce benzoic acid selectively. Under optimized conditions, SbIII-corrole@NF (NF = nickel foam) required an overpotential of 380 mV to reach a 50 mA cm-2 current density, comparable with those of other transition-metal-based complexes. On the other hand, replacing the anodic OER with benzyl alcohol oxidation lowered the required potential by 150 mV (at 300 mA cm-2) to improve the energy efficiency of the electrochemical process.

Ruthenium Azobis(benzothiazole): Electronic Structure and Impact of Substituents on the Electrocatalytic Single-Site Water Oxidation Process.

The present article deals with the structurally and spectroelectrochemically characterized newer class of ruthenium-azoheteroarenes [RuII(Ph-trpy)(Cl)(L)]ClO4, [1]ClO4-[3]ClO4 (Ph-trpy: 4'-phenyl-2,2':6',2″-terpyridine; L1: 2,2'-azobis(benzothiazole) ([1]ClO4); L2: 2,2'-azobis(6-methylbenzothiazole) ([2]ClO4); L3: 2,2'-azobis(6-chlorobenzothiazole) ([3]ClO4)). A collective consideration of experimental (i.e., structural and spectroelectrochemical) and theoretical (DFT calculations) results of [1]ClO4-[3]ClO4 established selective stabilization of (i) the unperturbed azo (N═N)0 function of L, (ii) the exclusive presence of the isomeric form involving the N(azo) donor of L trans to Cl, and (iii) the presence of extended, hydrogen-bonded trimeric units in the asymmetric unit of [2]ClO4 (CH---O) via the involvement of ClO4- anions. The detailed electrochemical studies revealed metal-based oxidation of [RuII(Ph-trpy)(Cl)(L)]+ (1+-3+) to [RuIII(Ph-trpy)(Cl)(L)]2+ (12+-32+); however, the electronic form of the first reduced state (1-3) could be better represented by its mixed RuII(Ph-trpy)(Cl)(L•-)/RuIII(Ph-trpy)(Cl)(L2-) state. Both native (1+-3+) and reduced (1-3) states exhibited weak lower energy transitions within the range of 1000-1200 nm. Further, [1]ClO4-[3]ClO4 delivered an electrochemical OER (oxygen evolution reaction) process in alkaline medium on immobilizing them to a carbon cloth support, which divulged an amplified water oxidation feature for [2]ClO4 due to the presence of electron-donating methyl groups in the L2 backbone. The faster OER kinetics and high catalytic stability of [2]ClO4 could also be rationalized by its lowest Tafel slope (85 mV dec-1) and choronoamperometric experiment (stable up to 12 h), respectively, along with high Faradic efficiency (∼97%). A comparison of [2]ClO4 with the reported analogous ruthenium complexes furnished its excellent intrinsic water oxidation activity.

Exploring Ligand-Controlled C2 Product Selectivity in Carbon Dioxide Reduction with Copper Metal-Organic Framework Nanosheets.

The suitable choice of an electrocatalyst is crucial in controlling the selectivity of electrocatalytic CO2 reduction products. Herein, we have explored the effect of different ligand environments in 2D metal-organic frameworks (MOFs), viz., copper naphthalenedicarboxylate (Cu-UNDC) and copper benzenedicarboxylate (Cu-UBDC). The change of ligand modulates the structure of the MOFs as well as the electronic environment around the copper center. The variation in the electronic structure and the coordination environment of the active Cu center changes the selectivity toward C2 products. In the electrocatalytic process, Cu-UNDC produced 24.3% Faradaic efficiency (FE) for the C2 products─far better than that of Cu-UBDC (13.2%). In contrast to electrocatalytic CO2RR, in the presence of light, Cu-UBDC (26.2%) achieved a better FE for the C2 products than Cu-UNDC (21.8%).

Visible light induced regioselective C-3 thiocyanation of imidazoheterocycles through naphthalimide dye based photoredox catalysis.

A visible light induced C-3 thiocyanation of imidazo[1,2-a]pyridines by using a naphthalimide based photoredox catalyst has been reported. Tolerance of electron withdrawing and donating groups at different positions of the imidazo[1,2-a]pyridine ring led to a wide substrate accessibility of this method. This methodology is further reproducible with other heterocycles like benzo[d]imidazo[2,1-b]thiazoles, indoles, azaindoles, and anilines.

Polyaniline coating enables electronic structure engineering in Fe3O4to promote alkaline oxygen evolution reaction.

The electronic structure of active sites is of importance for catalysts to achieve an optimized interaction with the intermediates. In this study, a unique organic-inorganic hybrid oxygen evolution reaction electrocatalyst composed of electrochemically inactive conducting polyaniline (PANI) and non-precious Fe-based oxide Fe3O4is presented. PANI molecules werein situloaded on Fe3O4nanoparticles through an efficient and simple process under mild conditions. The electronic structure of Fe3O4was modulated by creating a strong interaction with PANI molecules, leading to enhanced activity and stability of the catalyst to achieve 10 mA cm-2geometrical current density at overpotential of 265 mV in 1 M aqueous KOH solution. This work demonstrates that a highly efficient electrocatalyst can be achieved by molecular modification and provides a novel strategy for the optimization of the inactive non-precious catalysts.

Deciphering Ligand Controlled Structural Evolution of Prussian Blue Analogues and Their Electrochemical Activation during Alkaline Water Oxidation.

Herein, we have demonstrated the control over the structure of precatalysts to tune the properties of the active catalysts and their water oxidation activity. The reaction of K3 [Fe(CN)6 ] and Na2 [Fe(CN)5 (NO)] with Co(OH)2 @CC produced precatalysts PC-1 and PC-2, respectively, with distinct structural and electronic features. The replacement of the -CN group with strong π-acceptor -NO modulates the electronic and atomic structure of PC-2. As a result, a facile electrochemical transformation of PC-2 into active catalyst Fe-Co(OH)2 -Co(O)OH (AC-2) has been attained only in 15 CV cycles while 600 CV cycles are required for the electrochemical activation of PC-1 into AC-1. The X-ray absorption studies reveal the contraction of the Co-O and Fe-O bond in AC-2 because of the presence of a higher amount of Co3+ and Fe3+ than in AC-1. The high valent Co3+ and Fe3+ modulates the electronic properties of AC-2 and assists in the O-O bond formation, leading to the improved water oxidation activity.

Ruthenium-Benzothiadiazole Building Block Derived Dynamic Heterometallic Ru-Ag Coordination Polymer and Its Enhanced Water-Splitting Feature.

This article deals with the development of the unprecedented redox-mediated heterometallic coordination polymer {[RuIII(acac)2(µ-bis-η1-N,η1-N-BTD)2AgI(ClO4)]ClO4}n (3) via the oxidation of the monomeric building block cis-[RuII(acac)2(η1-N-BTD)2] (1) by AgClO4 (BTD = exodentate 2,1,3-benzothiadiazole, acac = acetylacetonate). Monomeric cis-[RuII(acac)2(η1-N-BTD)2] (1) and [RuII(acac)2(η1-N-BTD)(CH3CN)] (2) were simultaneously obtained from the electron-deficient BTD heterocycle and the electron-rich metal precursor RuII(acac)2(CH3CN)2 in refluxing CH3CN. Molecular identities of 1-3 were authenticated by their single-crystal X-ray structures as well as by solution spectral features. These results also reflected the elusive trigonal-planar geometry of the Ag ion in Ru-Ag-derived polymeric 3. Ru(III) (S = 1/2)-derived 3 displayed metal-based anisotropic EPR with ⟨g⟩/Δg = 2.12/0.56 and paramagnetically shifted 1H NMR. Spectroelectrochemistry in combination with DFT/TD-DFT calculations of 1n and 2n (n = 1+, 0, 1-) determined a metal-based (RuII/RuIII) oxidation and BTD-based reduction (BTD/BTD•-). The drastic decrease in the emission intensity and quantum yield but insignificant change in the lifetime of 3 with respect to 1 could be addressed in terms of static quenching and/or a paramagnetism-induced phenomenon. A homogeneously dispersed dumbbell-shaped morphology and the particle diameter of 3 were established by microscopic (TEM-EDX/SEM) and DLS analysis, respectively. Moreover, the dynamic nature of polymeric 3 was highlighted by its degradation to the η1-N-BTD coordinated monomeric fragment 1, which could also be followed spectrophotometrically in polar protic EtOH. Interestingly, both monomeric 1 and polymeric 3 exhibited efficient electrocatalytic activity toward water oxidation processes (OER, HER) on immobilization on an FTO support, which also divulged the better intrinsic water oxidation activity of 3 in comparison to 1.

Boosting Electrochemical Water Oxidation with Metal Hydroxide Carbonate Templated Prussian Blue Analogues.

The development of efficient and stable catalyst systems with low-cost, abundant, and non-toxic materials is the primary demand for electrochemical water oxidation. A unique method is reported for the syntheses of metal hydroxide carbonate templated Prussian blue analogues (PBAs) on carbon cloth and their outstanding water oxidation activities in alkaline medium. The best water oxidation activity is obtained with cobalt hydroxide carbonate templated t-CoII -CoIII with an overpotential as low as 240 mV to reach a current density of 10 mA cm-2 . It produces constant current over 50 h in chronoamperometric measurements. Moreover, the catalysts outperform the activities of the PBAs prepared without any template and even the noble metal catalyst RuO2 . Spectroscopic and microscopic studies show that the PBAs are transformed into layered hydroxide-oxyhydroxide structures during electrochemical process and provide the active sites for the water oxidation.

Boosting Visible-Light-Driven Photocatalytic Hydrogen Evolution with an Integrated Nickel Phosphide-Carbon Nitride System.

Solar light harvesting by photocatalytic H2 evolution from water could solve the problem of greenhouse gas emission from fossil fuels with alternative clean energy. However, the development of more efficient and robust catalytic systems remains a great challenge for the technological use on a large scale. Here we report the synthesis of a sol-gel prepared mesoporous graphitic carbon nitride (sg-CN) combined with nickel phosphide (Ni2 P) which acts as a superior co-catalyst for efficient photocatalytic H2 evolution by visible light. This integrated system shows a much higher catalytic activity than the physical mixture of Ni2 P and sg-CN or metallic nickel on sg-CN under similar conditions. Time-resolved photoluminescence and electron paramagnetic resonance (EPR) spectroscopic studies revealed that the enhanced carrier transfer at the Ni2 P-sg-CN heterojunction is the prime source for improved activity.

Unification of catalytic water oxidation and oxygen reduction reactions: amorphous beat crystalline cobalt iron oxides.

Catalytic water splitting to hydrogen and oxygen is considered as one of the convenient routes for the sustainable energy conversion. Bifunctional catalysts for the electrocatalytic oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are pivotal for the energy conversion and storage, and alternatively, the photochemical water oxidation in biomimetic fashion is also considered as the most useful way to convert solar energy into chemical energy. Here we present a facile solvothermal route to control the synthesis of amorphous and crystalline cobalt iron oxides by controlling the crystallinity of the materials with changing solvent and reaction time and further utilize these materials as multifunctional catalysts for the unification of photochemical and electrochemical water oxidation as well as for the oxygen reduction reaction. Notably, the amorphous cobalt iron oxide produces superior catalytic activity over the crystalline one under photochemical and electrochemical water oxidation and oxygen reduction conditions.

The low loading of metal in metal-organic framework-derived NiNx@NC promotes amide formation through C-N coupling.

The pyrolysis of Ni-substituted zeolitic imidazolate framework-8 produces NiNx@NC with an ultra-low loading of Ni (7.4 × 10-6 mol%). The Ni-N coordination, subnanometer particle size, and uniform distribution of NiNx on the NC support lead to excellent catalytic activity (TON = 2702) and selectivity for the amination of aldehydes to produce amides.

Nitrate-coordinated FeNi(OH)2 for hydrazine oxidation assisted seawater splitting at the industrial-level current density.

In this study, we developed a nitrate-coordinated iron-nickel hydroxide [NC-FeNi(OH)2] catalyst for hydrazine oxidation-assisted seawater splitting. Replacement of O2 evolution by hydrazine oxidation in a two-electrode setup resulted in a cell voltage of 1.20 V at 100 mA cm-2. This represents a voltage reduction of 470 mV compared to conventional seawater splitting. Additionally, NC-FeNi(OH)2 demonstrated remarkable stability over a period of 60 hours.

Visible light-driven molecular oxygen activation for oxidative amidation of alcohols using lead-free metal halide perovskite.

Herein, we report the modulation of the band structures of halide perovskite Cs2CuBr4 by tuning the synthesis methods. The photocatalyst PC-1, synthesized by the hot injection method, has a more negative conduction band minima (CBM) than the photocatalyst PC-2, synthesized at room temperature. As a result, PC-1 can activate molecular O2 more efficiently to initiate the radical-mediated dehydrogenation of alcohols. The more positive valence band maxima (VBM) of PC-1 also facilitates amine oxidation to the corresponding radical. Further, improved charge separation and transport and a decrement in the photogenerated charge carrier recombination have been detected for PC-1 to enhance photocatalytic activity. PC-1 showed improved yields for a series of structurally diverse amides (highest yield = 98%) by oxidative amidation of alcohols under visible light irradiation.

The isomer-sensitive electrochemical HER of ruthenium(II)-hydrido complexes involving redox-active azoheteroaromatics.

The article deals with the development of isomeric ruthenium(II)-hydrido complexes [RuII(H)(L1)(PPh3)2(CO)]ClO4 ([1a]ClO4-[1b]ClO4)/[RuII(H)(L2)(PPh3)2(CO)]ClO4 ([2a]ClO4-[2b]ClO4) involving azo coupled L1 [L1: (E)-1,2-bis(1-methyl-1H-pyrazol-3-yl)diazene]/L2 [L2: (E)-1,2-bis(4-iodo-1-methyl-1H-pyrazol-3-yl)diazene], respectively. Structural evaluation of the complexes affirmed the syn conformation of the coordinated/uncoordinated pyrazole groups of L and its unperturbed neutral azo (NN) state. Isomeric forms in [1a]ClO4/[1b]ClO4 or [2a]ClO4/[2b]ClO4 differed with respect to the cis and trans orientations of the coordinated CO and N(azo) donor of L, respectively. It also demonstrated the formation of intermolecular hydrogen-bonded dimeric or 1D-polymeric chains in [1a]ClO4/[2b]ClO4 or [1b]ClO4, respectively. Successive two-electron reductions of the complexes varied to an appreciable extent as a function of the heterocycles connected to L. The involvement of the azo function of L towards the reductions ([NN]0 → [NN]˙- → [NN]2-) was supported by the DFT calculated MOs and Mulliken spin density at the paramagnetic state, which was further validated by the radical EPR profile of the first reduced (S = 1/2) state. Isomeric [1a]ClO4/[1b]ClO4 or [2a]ClO4/[2b]ClO4 immobilised on the carbon cloth support underwent various electrochemical acidic HERs (hydrogen evolution reactions) with TOF/10-1 s-1: [1a]ClO4 (0.83) > [1b]ClO4 (0.68) > [2a]ClO4 (0.50) > [2b]ClO4 (0.37).

Deciphering charge transfer dynamics of a lead halide perovskite-nickel(ii) complex for visible light photoredox C-N coupling.

Photoredox catalysis involving perovskite quantum dots (QDs) has gained enormous attention because of their high efficiency and selectivity. In this study, we have demonstrated CsPbBr3 QDs as photocatalysts for the C-N bond formation reaction. The introduction of Ni(dmgH)2 (dmgH = dimethyl glyoximato) as a cocatalyst with CsPbBr3 QDs facilitates photocatalytic C-N coupling to form a wide variety of amides. The optimized interaction between the cocatalyst and photocatalyst enhances charge transfer and mitigates charge recombination, ultimately boosting photocatalytic performance. The photocatalytic activity is notably influenced by the variation in the amount of cocatalyst and 7 wt% Ni(dmgH)2 produces the best yield (92%) of amide. Femtosecond transient absorption spectroscopy reveals that the dynamics of the trap states of QDs are affected by cocatalyst. Further, Ni(dmgH)2 facilitates molecular oxygen activation to form superoxide radicals, which further initiates the radical pathway for the C-N coupling.

Dual-Mode Virus Detection: Combining Electrochemical and Fluorescence Modalities for Enhanced Sensitivity and Reliability.

This study introduces a dual-mode biosensor specifically designed for the quantitative detection of viruses in rapid analysis. The biosensor is unique in its use of both optical (fluorescence) and electrochemical (impedance) detection methods using the same nanocomposites, providing a dual confirmation system for virus (norovirus-like particles) quantification. The system is based on using two antibody-conjugated nanocomposites: CdSeS quantum dots and Au-N,S-GQD nanocomposites. For optical detection, the principle relies on the fluorescence quenching of CdSeS by Au-N,S-GQD in a sandwich structure with the target. Conversely, electrochemical detection is based on the change in impedance caused by the formation of the same sandwich structure. The biosensor demonstrated exceptional sensitivity, capable of detecting norovirus at concentrations of as low as femtomolar in the electrochemical method and picomolar in the optical method. In the dual-responsive concentration range from 10-13 to 10-10 M, the sensor is highly sensitive in both methods, creating significant changes in fluorescence intensity and impedance in the presence of virus. Furthermore, the biosensor exhibits a high degree of specificity, with a negligible response to nontarget proteins, even within complex test solutions. This work represents a significant advancement in the field of biosensor technology, offering a fast, accurate, and reliable method for diagnosing viral infections and diseases.

Superior electrocatalytic hydrogen evolution activity of a triply bridged diruthenium(II) complex on a carbon cloth support.

This article describes the structural authentication of a unique triply bridged [1](ClO4)2 and monomeric [2]ClO4/[3]ClO4. Electrochemical HER on a carbon cloth support demonstrated the superior performance of [1](ClO4)2 with high TON (>105) and its long-term stability. The primary kinetic isotope effect of [1](ClO4)2 revealed the involvement of PCET in the rate-determining step.

Structural modification of nickel tetra(thiocyano)corroles during electrochemical water oxidation.

In this study, we present two fully characterized nickel tetrathiocyanocorroles, representing a novel class of 3d-metallocorroles. These nickel(II) ions form square planar complexes, exhibiting a d8-electronic configuration. These anionic complexes are stabilized by the electron-withdrawing SCN groups on the bipyrrole unit of the corrole. The reduced aromaticity in these anionic nickel(II) corrole complexes is evidenced by single crystal X-ray diffraction (XRD) data and a markedly altered absorption profile, with stronger Q bands compared to Soret bands. Notably, the UV-Vis and electrochemical data exhibit significant differences from previously reported nickel(II) corrole radical cation and nickel(II) porphyrin complexes. While these electrochemical data bear a resemblance to those of the anionic nickel(II) corrole by Gross et al., the UV-Vis data show substantial distinctions. Additionally, we explore the utilization of nickel(II)-corrole@CC (where CC denotes carbon cloth) as an electrocatalyst for the oxygen evolution reaction (OER) in an alkaline medium. During electrochemical water oxidation, the molecular catalyst is partially converted to nickel (oxy)hydroxide, Ni(O)OH. The structure reveals the coexistence of the molecular complex and Ni(O)OH in the active catalyst, achieving a turnover frequency (TOF) of 3.32 × 10-2 s-1. The synergy between the homogeneous and heterogeneous phases improves the OER activity, providing more active sites and edge sites and enhancing interfacial charge transfer.

Axial ligand-induced high electrocatalytic hydrogen evolution activity of molecular cobaloximes in homo- and heterogeneous medium.

Three new molecular cobaloxime complexes with the general formula [ClCo(dpgH)2L] (1-3), where L1 = N-(4-pyridylmethyl)-1,8-naphthalimide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalimide, L3 = 4-piperidin-N-(4-pyridylmethyl)-1,8-naphthalimide, have been synthesized and characterized by UV-Vis, multinuclear NMR, FT-IR and PXRD spectroscopic techniques. The crystal structures of all complexes have also been reported. The electrocatalytic activity of complexes is investigated under two catalysis conditions: (i) homogeneous conditions in acetonitrile using acetic acid (AcOH) as a proton source and (ii) heterogeneous conditions upon immobilization onto the surface of activated carbon cloth (CC). Complex 3 exhibited high electrocatalytic HER activity under both homogeneous and heterogeneous conditions. It catalyses proton reduction to molecular hydrogen in acetonitrile solution at a lower overpotential (640 mV) with a high turnover frequency (TOF) of 524.57 s-1 and demonstrates good stability in acidic conditions. Furthermore, catalytic (working) electrodes are prepared by immobilizing the complexes onto the surface of activated carbon cloth (CC) for electrocatalytic HER under heterogeneous conditions. An impressive HER performance was again obtained with catalytic electrode 3@CC in 1.0 M KOH, achieving a current density of -10 mA cm-2 at an overpotential of 262 mV. Chronoamperometric (CA) studies showed no significant decay of the initial current density for 10 h, indicating the excellent stability of 3@CC. Additionally, UV-Vis and NMR spectral studies of the recovered catalyst after electrocatalysis revealed no structural changes, demonstrating its robustness under reaction conditions.

4f-2p-3d orbital overlap in a metal-organic framework-derived CeO2/CeCo-LDH heterostructure promotes water oxidation.

Herein, we have demonstrated a facile method for the synthesis of CeO2/Ce-Co-LDH heterostructures using zeolitic imidazolate framework-67 as the precursor. The Ce-incorporation in Co-LDH results in 4f-2p-3d orbital overlap to tune the electronic structure whereas the oxygen-deficient CeO2 controls the interface charge transfer. This results in excellent water oxidation activity to attain 500 mA cm-2 current density at 320 overpotential.