The rising global need for sustainable energy has intensified research into environmentally friendly energy conversion technologies, such as fuel cells and electrochemical water splitting devices. The efficiency of these technologies is strongly influenced by the activity of electrocatalysts that enable the oxygen reduction (ORR) and evolution (OER) reactions. Noble metal-based electrocatalysts, including Pt, Pd, RuO2 and IrO2, are widely regarded as benchmark materials for these reactions due to their excellent electrocatalytic activity; nevertheless, their high cost, scarcity and limited long-term stability have prompted the development of alternatives. Polyoxometalates (POMs) have attracted considerable interest as a versatile class of materials, owing to their adjustable structures, redox properties and potential to serve as efficient and economically viable catalysts. In this research, we investigate two sandwich-type Dawson POM clusters containing cobalt and nickel ([CoNi3(As2W15O56)2]16- and [NiCo3(As2W15O56)2]16-) but with different spatial arrangements. The prepared electrocatalysts exhibited notable OER activity in alkaline media, achieving maximum current densities of 86.70 and 68.32 mA cm-2 with corresponding overpotential values of 0.45 and 0.49 V vs. RHE, respectively. The electrocatalysts also demonstrated promising activity towards the ORR, with diffusion-limiting current densities of -2.98 and -2.33 mA cm-2 and onset potentials of 0.82 and 0.78 V vs. RHE, respectively. This paper provides evidence suggestive of an influence of the metal centre position within the POM framework on the ORR/OER electrochemical performance and reinforces the potential of these hybrid materials as cost-effective and sustainable bifunctional electrocatalysts for next-generation energy devices.
Three new copper(I) complexes derived from N,N'-dialkyl-β-dialdiminate anions (alkyl = iso-propyl or tert-butyl) are reported. Treatment of CuBr with Li[tBuN(CH)3NtBu] affords the tetrameric copper(I) compound Cu4[tBuN(CH)3NtBu]4. In this tetramer, the β-dialdiminate ligands adopt open-chain conformations that link the copper(I) centers into a boat-shaped 24-membered ring. Interestingly, the tetramer dissociates over several hours in solution into a dimer of stoichiometry Cu2[tBuN(CH)3NtBu]2. When copper(II) chloride is treated with Li[tBuN(CH)3NtBu], or copper(II) methoxide is treated with H[iPrN(CH)3NiPr], redox reactions take place in which the metal center is reduced to copper(I) and the β-dialdiminate anion or β-dialdimine is oxidized. Two copper(I) complexes containing oxidized β-dialdiminate groups have been isolated: in both complexes, the oxidized group has been dehydrogenated and oligomerized through C-C bond formation. All three compounds have been characterized by X-ray crystallography; selected NMR, IR, EA, and UV-Vis spectra are also reported.
The reaction rate of small ring cycloalkane transformations is primarily governed by strain release. The present study summarises how the interplay between substrate strain release and orbital orientations from the transition metal catalyst affects overall catalytic efficiency. Density functional theory (DFT) studies on a Rh(I) metal complex in a [5 + 1] cycloaddition reaction between vinylcyclopropane and CO are summarized. The free energy barriers for oxidative addition on singlet (7.7 kcal mol-1) and triplet (25.6 kcal mol-1) surfaces highlight how optimal orbital orientation in transition metal catalysts synergizes with strain release. The distortion-interaction energy analysis of singlet and triplet states confirmed the mechanism of synergy between strain release and orbital interaction. Distinct spin states tune the kinetics by modulating strain relief and electronic arrangements and effectively lower activation energies, enabling efficient [5 + 1] metal catalysed cycloadditions.
Solar-driven water-splitting represents a promising method of producing H2 gas as a clean, renewable, and alternative fuel source. While proton reduction is thermodynamically more favorable in acidic pHs, hydrogen evolution reaction (HER) in neutral and basic media may be preferred for its coupling to the oxidation of water for overall water splitting. To further understand the electronic and steric effects that govern the structure-function relationships in catalytic HER, molecular Co complexes based on a pentadentate tetrapyridylamine ligand containing a phenol group were synthesized, characterized, and studied for photocatalytic HER. The octahedral CoII-chloride complex with a dangling phenol group can be converted to a trigonal bipyramidal CoII complex featuring a bound phenolate and a dangling pyridine moiety in aqueous solutions. The resulting Co complex with trigonal bipyramidal geometry shows considerable activity and improved stability for photocatalytic HER in purely basic aqueous solutions with turnover numbers ranging from 11 900-13 700 in pH 7-9 solutions. Results from DFT computations suggest either a modified electron transfer (E)-proton transfer (C)-electron transfer (E)-proton transfer (C) (mod-ECEC) or mod-CEEC pathway for HER depending on the protonation state of the ligand.
Embedding photoactive coordination complexes within redox-active layered oxides offers a route to couple molecular excited-state chemistry with inorganic electrode reactions. Here, [Ru(bpy)3]2+-intercalated layered MnO2 was electrodeposited on a conductive bamboo-charcoal/carbon-nanotube composite and used as an anode for H2 evolution at a Pt cathode. At +1.10 V vs. Ag/AgCl in 0.5 M Na2SO4, three independent experiments yielded 0.87 ± 0.15 mL H2 after 3 h under 300 nm irradiation, 4.4 times the dark value (0.20 ± 0.05 mL), with a faradaic efficiency of 80.3 ± 14.4%. Although incident and estimated absorbed photon flux densities at 450 and 600 nm exceeded those at 300 nm by more than 400-fold, the 300 nm condition produced the largest H2 evolution and total charge, excluding a simple light-intensity or whole-electrode-absorption explanation. Post-electrolysis spectroscopy, ICP-MS, and semiquantitative redox-potential analysis support a model in which photoexcitation of interlayer [Ru(bpy)3]2+ contributes to Mn(III)/Mn(IV)-related redox cycling, while the elementary electron-transfer and ionic charge-compensation pathways remain unresolved. These findings show that interlayer coordination-complex design can couple molecular photoexcitation with redox-active layered oxide electrodes for light-assisted hydrogen generation.
Triple-negative breast cancer (TNBC) is an aggressive disease with limited treatment options due to the absence of ER, PR, and HER2 receptors. This review summarises the recent progress in the use of ruthenium, iridium, and rhenium complexes as alternative therapeutic agents for TNBC. These metal complexes are designed to respond to tumor-specific biomarkers or the tumor microenvironment, enabling selective uptake and enhanced anticancer activity. Through redox reactions and light activation, they generate reactive oxygen species, disrupt mitochondrial function, and induce cancer cell death. Overall, ruthenium, iridium, and rhenium complexes offer a multi-mechanistic and targeted approach that may help overcome resistance and improve future TNBC treatment strategies.
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