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Herein, we present a dark-green crystalline tetranuclear Cu(II) Schiff base complex {C1 = [Cu4L4](ClO4)4(DMF)4(H2O)} using a N,N,O donor ligand (HL), namely 2-(((2-hydroxypropyl)imino)methyl)-6-methoxyphenol. Spectro-photometrical investigation on the β-lactamase-like activity of this coordinately saturated system revealed its catalytic inefficiency towards hydrolysis of nitrocefin as a model substrate. This complex has attracted significant interest as a promising photo-catalyst owing to its narrow band gap (2.40 eV) as predicted from DFT calculations and its higher responsivity towards UV light. Therefore, C1 is effectively involved in the photocatalytic reduction of perchlorate to Cl− in the presence of a hole scavenger (H2O–MeOH) under prolonged UV irradiation and itself becomes photo-cleaved to yield a new dark-brown colored chlorobridged dinuclear crystalline complex C2 {[CuL(H2O)2Cl3]H2O}. Furthermore, C2 was deployed as a functional β-lactamase model and was found to show a remarkable catalytic proficiency towards the hydrolysis of nitrocefin in 70 : 30 (V/V) MeOH–H2O medium. This pro-catalyst C2 has been speculated to generate an aqua bridged active catalyst that plays a crucial factor in hydrolysis. This phenomenon was again experimentally established by potentiometric pH titration where C2 displays only one pKa value (7.11) in the basic pH range, indicating the deprotonation of the bridged water molecule. Based on several other kinetic studies, it may be postulated that the hydrolysis of nitrocefin is initiated by the nucleophilic attack of a bridging hydroxide, followed by very fast protonation of the intermediate to furnish the hydrolyzed product. It is noteworthy that the rate of nitrocefin hydrolysis is greatly inhibited in the presence of external chloride concentration. To the best of our knowledge, this is the first report on the photochemical behavior of such a tetranuclear copper(II) Schiff base complex. Our current interest is focused on inventing a potent β-lactamase inhibitory therapeutic as well as elucidating its mechanism through comprehensive chemical analysis. [ABSTRACT FROM AUTHOR]

Hydrogen obtained from renewable sources such as water and alcohols is regarded as an efficient clean-burning alternative to non-renewable fuels. The use of the so-called bio-H2 regardless of its colour will be a significant step towards achieving global net-zero carbon goals. Challenges still persist however with conventional H2 storage, which include low-storage density and high cost of transportation apart from safety concerns. Global efforts have thus focussed on liquid organic hydrogen carriers (LOHCs), which have shown excellent potential for H2 storage while allowing safer large-scale transformation and easy on-site H2 generation. While water could be considered as the most convenient liquid inorganic hydrogen carrier (LIHC) on a long-term basis, the utilization of alcohols as LOHCs to generate on-demand H2 has tasted instant success. This has helped to draw a road-map of futuristic H2 storage and transportation. The current review brings to the fore the state-of-the-art developments in hydrogen generation from readily available, feed-agnostic bio-alcohols as LOHCs using molecular transition-metal catalysts. [ABSTRACT FROM AUTHOR]

During the past few decades, the synthesis of coordination complexes that exhibit high catalytic efficiencies has received significant attention from bio-inorganic chemists. In this context, two trinuclear mixed-valence manganese complexes, namely [MnIII2MnII(L1)2(OAc)4(H2O)2]·5H2O (1) and [MnIII2MnII(L2)2(OAc)4(CH3OH)2]·3CH3OH (2) [OAc = acetate] have been synthesized and structurally characterized. These complexes are shown to retain their nuclearity in acetonitrile medium, unveiling a new area of catecholase-like activity. In fact, both complexes showed an efficient oxidizing activity in acetonitrile using 3,5-di-tert-butylcatechol (3,5-DTBC) as the model substrate, and they were able to bring about complete oxidation of the substrate at a catalyst-to-substrate ratio of up to 1 : 600. To the best of our knowledge, the catecholase-like activity of trinuclear species is explored here for the first time. Interestingly, pseudo-zero-order kinetics with respect to the substrate are identified for both complexes, which represents the second report of this type of activity and the first report observed for a mixed-valence manganese complex. Details from experimental investigations of the mechanistic pathway revealed that the formation of oxygen radicals is believed to be the rate-limiting step, which supports the observation of the pseudo-zeroth-order kinetics. [ABSTRACT FROM AUTHOR]

ConspectusElectrochemical CO 2 reduction to obtain formate or formic acid is receiving significant attention as a method to combat the global warming crisis. Significant efforts have been devoted to the advancement of CO 2 reduction techniques over the past few decades. This Account provides a unified discussion on various electrochemical methodologies for CO 2 to formate conversion, with a particular focus on recent advancements in utilizing 3d-transition-metal-based molecular catalysts. This Account primarily focuses on understanding molecular functions and mechanisms under homogeneous conditions, which is essential for assessing the optimized reaction conditions for molecular catalysts. The unique architectural features of the formate dehydrogenase (FDH) enzyme provide insight into the key role of the surrounding protein scaffold in modulating the active site dynamics for stabilizing the key metal-bound CO 2 intermediate. Additionally, the protein moiety also triggers a facile proton relay around the active site to drive electrocatalytic CO 2 reduction forward. The fine-tuning of FDH machinery also ensures that the electrocatalytic CO 2 reduction leads to the production of formic acid as the major yield without any other carbonaceous products, while limiting the competitive hydrogen evolution reaction. These lessons from the enzymes are key in designing biomimetic molecular catalysts, primarily based on multidentate ligand scaffolds containing peripheral proton relays. The subtle modifications of the ligand framework ensure the favored production of formic acid following electrocatalytic CO 2 reduction in the solution phase. Next, the molecular catalysts are required to be mounted on robust electroactive surfaces to develop their corresponding heterogeneous versions. The surface-immobilization provides an edge to the molecular electrocatalysts as their reactivity can be scaled up with improved durability for long-term electrocatalysis. Despite challenges in developing high-performance, selective catalysts for the CO 2 to formic acid transformation, significant progress is being made with the tactical use of graphene and carbon nanotube-based materials. To date, the majority of the research activity stops here, as the development of an operational CO 2 to formic acid converting electrolyzer prototype still remains in its infancy. To elaborate on the potential future steps, this Account covers the design, scaling parameters, and existing challenges of assembling large-scale electrolyzers. A short glimpse at the utilization of electrolyzers for industrial-scale CO 2 reduction is also provided here. The proper evaluation of the surface-immobilized electrocatalysts assembled in an electrolyzer is a key step for gauging their potential for practical viability. Here, the key electrochemical parameters and their expected values for industrial-scale electrolyzers have been discussed. Finally, the techno-economic aspects of the electrolyzer setup are summarized, completing the journey from tactical design of molecular catalysts to their appropriate application in a commercially viable electrolyzer setup for CO 2 to formate electroreduction. Thus, this Account portrays the complete story of the evolution of a molecular catalyst to its sustainable application in CO 2 utilization.

This work illustrates the practicality and economic benefits of employing a hetero-interfaced electrocatalyst (CoS 2 @CoFe-LDH), containing cobalt sulphide and iron-cobalt double-layer hydroxide for large-scale hydrogen generation. Here, the rational synthesis and detailed characterization of the CoS 2 @CoFe-LDH material to unravel its unique heterostructure are essayed. The CoS 2 @CoFe-LDH operates as a bifunctional electrocatalyst to trigger both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline seawater (pH 14.0) while showcasing low overpotential requirement for HER (311 mV) and OER (450 mV) at 100 mA cm - 2 current density. The identical CoS 2 @CoFe-LDH on either electrode in an H-cell setup results in simultaneous H 2 and O 2 production from seawater with a ≈98% Faradaic efficiency with an applied potential of 1.96V@100 mA cm - 2 . Next, this CoS 2 @CoFe-LDH catalyst is deployed on both sides of a membrane electrode assembly in a one-stack electrolyzer, which retains the intrinsic bifunctional reactivity of the catalyst to generate H 2 and O 2 in tandem from alkaline seawater with an impeccable energy efficiency (50 kWh kg -1 -of-H 2 ). This electrolyzer assembly can be directly linked with a Si-solar cell to produce truly green hydrogen with a solar-to-hydrogen generation efficiency of 15.88%, highlighting the potential of this converting seawater to hydrogen under solar irradiation., (© 2024 Wiley‐VCH GmbH.)