Photoactivation of titanium-oxo cluster [Ti6O6(OR)6(O2C t Bu)6]: mechanism, photoactivated structures, and onward reactivity with O2 to a peroxide complex.

The molecular titanium-oxo cluster [Ti6O6(OiPr)6(O2C t Bu)6] (1) can be photoactivated by UV light, resulting in a deeply coloured mixed valent (photoreduced) Ti (iii/iv) cluster, alongside alcohol and ketone (photooxidised) organic products. Mechanistic studies indicate that a two-electron (not free-radical) mechanism occurs in this process, which utilises the cluster structure to facilitate multielectron reactions. The photoreduced products [Ti6O6(OiPr)4(O2C t Bu)6(sol)2], sol = iPrOH (2) or pyridine (3), can be isolated in good yield and are structurally characterized, each with two, uniquely arranged, antiferromagnetically coupled d-electrons. 2 and 3 undergo onward oxidation under air, with 3 cleanly transforming into peroxide complex, [Ti6O6(OiPr)4(O2C t Bu)6(py)(O2)] (5). 5 reacts with isopropanol to regenerate the initial cluster (1) completing a closed cycle, and suggesting opportunities for the deployment of these easily made and tuneable clusters for sustainable photocatalytic processes using air and light. The redox reactivity described here is only possible in a cluster with multiple Ti sites, which can perform multi-electron processes and can adjust its shape to accommodate changes in electron density.

Synthesis of a nanoscale Cu(II)31-oxo-carboxylate cluster, and effect of Cu-oxo cluster size on visible-light absorption.

Cu16-Cu31 Cu(II)-oxo-carboxylate clusters are reported, including those with condensed 1.5 nm Cu-O cores supported exclusively by O-donor ligands. A size-colour correlation is observed due to a red-shift of the charge transfer absorption band on increasing size; hence these clusters sit between small molecules and (black) CuO nanostructures.

Floating perovskite-BiVO4 devices for scalable solar fuel production.

Photoelectrochemical (PEC) artificial leaves hold the potential to lower the costs of sustainable solar fuel production by integrating light harvesting and catalysis within one compact device. However, current deposition techniques limit their scalability1, whereas fragile and heavy bulk materials can affect their transport and deployment. Here we demonstrate the fabrication of lightweight artificial leaves by employing thin, flexible substrates and carbonaceous protection layers. Lead halide perovskite photocathodes deposited onto indium tin oxide-coated polyethylene terephthalate achieved an activity of 4,266 µmol H2 g-1 h-1 using a platinum catalyst, whereas photocathodes with a molecular Co catalyst for CO2 reduction attained a high CO:H2 selectivity of 7.2 under lower (0.1 sun) irradiation. The corresponding lightweight perovskite-BiVO4 PEC devices showed unassisted solar-to-fuel efficiencies of 0.58% (H2) and 0.053% (CO), respectively. Their potential for scalability is demonstrated by 100 cm2 stand-alone artificial leaves, which sustained a comparable performance and stability (of approximately 24 h) to their 1.7 cm2 counterparts. Bubbles formed under operation further enabled 30-100 mg cm-2 devices to float, while lightweight reactors facilitated gas collection during outdoor testing on a river. This leaf-like PEC device bridges the gulf in weight between traditional solar fuel approaches, showcasing activities per gram comparable to those of photocatalytic suspensions and plant leaves. The presented lightweight, floating systems may enable open-water applications, thus avoiding competition with land use.

Titanium compounds containing naturally occurring dye molecules.

A range of titanium compounds containing the naturally occurring dyes quinizarin (QH2) and alizarin (AH2) was synthesized and structurally characterized in the solid state. Among these is the first examples of a discrete metallocyclic arrangement formed exclusively using quinizarin ligands and the first examples of lanthanide containing titanium compounds of the alizarin family of ligands.

Antibacterial Surfaces with Activity against Antimicrobial Resistant Bacterial Pathogens and Endospores.

Hospital-acquired bacterial infections are a significant burden on healthcare systems worldwide causing an increased duration of hospital stays and prolonged patient suffering. We show that polyurethane containing crystal violet (CV) and 3-4 nm zinc oxide nanoparticles (ZnO NPs) possesses excellent bactericidal activity against hospital-acquired pathogens including multidrug resistant Escherichia coli (E. coli), Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA), and even highly resistant endospores of Clostridioides (Clostridium) difficile. Importantly, we used clinical isolates of bacterial strains, a protocol to mimic the environmental conditions of a real exposure in the healthcare setting, and low light intensity equivalent to that encountered in UK hospitals (∼500 lux). Our data shows that ZnO NPs enhance the photobactericidal activity of CV under low intensity light even with short exposure times, and we show that this involves both Type I and Type II photochemical pathways. Interestingly, polyurethane containing ZnO NPs alone showed significant bactericidal activity in the dark against one strain of E. coli, indicating that the NPs possess both light-activated synergistic activity with CV and inherent bactericidal activity that is independent of light. These new antibacterial polymers are potentially useful in healthcare facilties to reduce the transmission of pathogens between people and the environment.

The use of mixed-metal single source precursors for the synthesis of complex metal oxides.

Complex metal oxides, defined as metal oxide materials with multiple metals, phases or including dopants, are used in a huge variety of modern applications ranging from photocatalysis, transparent conductive materials, supercapacitors and battery components. In this feature article, the use of mixed-metal single source precursors to synthesise complex metal oxides is explored. The structures and decomposition/reaction pathways of various precursors including mixed-metal alkoxides, complexes with chelating ligands, clusters, polyoxometallates, and metal-organic frameworks are discussed. The advantages and opportunities of using a single source precursor strategy are investigated and highlighted.

Photo-redox reactivity of titanium-oxo clusters: mechanistic insight into a two-electron intramolecular process, and structural characterisation of mixed-valent Ti(iii)/Ti(iv) products.

Small titanium-oxo-alkoxide clusters, [TiO(OR)(O2PR'2)]4, synthesised by the stoichiometric reaction of Ti(OiPr)4, phosphinic acid and water, undergo a photo-redox transformation under long-wave UV light. The photo-reaction generates blue coloured, mixed-valence Ti(iii)/Ti(iv)-oxo clusters alongside acetone and isopropanol by-products. This reactivity indicates the ability for photoactivated charge separation to occur in even the smallest of Ti-oxo clusters. EPR and NMR spectroscopic studies support a photo-redox mechanism that occurs via an intramolecular, two-electron pathway, directly relating to current doubling effects observed at TiO2 photoanodes in the presence of alcohols. The rate of photo-reaction is solvent dependent, with donor solvents supporting the formation of low coordinate Ti(iii) sites. The nature of the electronic transition is identified by DFT and TDDFT calculations as an oxygen to titanium charge transfer and it is possible to finetune the UV absorption onset observed by changing the phosphinate ligand. A two-electron photo-reduced cluster, [Ti4O4(O2PPh2)6], forms spontaneously from the photo-reaction and its structure is identified by X-ray crystallography with supporting DFT calculations. These indicate that [Ti4O4(O2PPh2)6] is high-spin and contains two ferromagnetically coupled electrons delocalised over the Ti4 core. [Ti4O4(O2PPh2)6] undergoes rapid oxidation in air in the solid-state and performs a remarkable single-crystal to single-crystal transformation, to form a stable cluster-superoxide salt.

A simple one-step synthetic route to access a range of metal-doped polyoxovanadate clusters.

VO(OiPr)3 is a useful precursor for the synthesis of a range of metal-doped polyoxovanadate (POV) cage compounds, its reactions with hydrated metal salts providing a route to arrangements containing Bi and other main group metals, transition metals and lanthanides. The new POV compounds [Bi2(DMSO)6V12O33Br]2[M(DMSO)6] (2Br-M, M = CoII, NiII, CuII, ZnII) [Bi2(DMSO)6V12O33Cl]2[Ca(DMSO)x]·yDMSO (2Cl-Ca), [Bi2(DMSO)6V12O33Cl]2[LnCl(DMSO)7] (2Cl-Ln, Ln = LaIII, CeIII, EuIII), [Bi2(DMSO)6V10O28F2]3[Bi(DMSO)5]2 (3), [V12O32(DMSO)][Gd(NO3)(DMSO)5.5]2 (4) and [Ln(DMSO)4V12O32Cl][LnCl(DMSO)7] (5Cl-Ln, Ln = CeIII, EuIII) have been structurally characterised, and their properties studied using UV-Vis spectroscopy and cyclic voltammetry. Drop-casting these compounds onto fluorine-doped tin oxide followed by calcination provides a simple approach to thin films of metal-doped BiVO4 or LnVO4, depending on the composition of the cage precursor. The applications of the BiVO4 films as photoanodes for water oxidation is explored, with transition metal doping of BiVO4 improving the activity (∼1.8-2.4 times the photocurrent density of undoped BiVO4 at 1.23 V vs. RHE) while lanthanide or Ca-doping is detrimental.

Single-Source Bismuth (Transition Metal) Polyoxovanadate Precursors for the Scalable Synthesis of Doped BiVO4 Photoanodes.

Single-source precursors are used to produce nanostructured BiVO4 photoanodes for water oxidation in a straightforward and scalable drop-casting synthetic process. Polyoxometallate precursors, which contain both Bi and V, are produced in a one-step reaction from commercially available starting materials. Simple annealing of the molecular precursor produces nanocrystalline BiVO4 films. The precursor can be designed to incorporate a third metal (Co, Ni, Cu, or Zn), enabling the direct formation of doped BiVO4 films. In particular, the Co- and Zn-doped photoanodes show promise for photoelectrochemical water oxidation, with photocurrent densities >1 mA cm-2 at 1.23 V vs reversible hydrogen electrode (RHE). Using this simple synthetic process, a 300 cm2 Co-BiVO4 photoanode is produced, which generates a photocurrent of up to 67 mA at 1.23 V vs RHE and demonstrates the scalability of this approach.

Layered zinc hydroxide monolayers by hydrolysis of organozincs.

2D inorganic materials and their exfoliated counterparts are both of fundamental interest and relevant for applications including catalysis, electronics and sensing. Here, a new bottom-up synthesis route is used to prepare functionalised nanoplatelets, in apolar organic solvents, via the hydrolysis of organometallic reagents; the products can be prepared in high yield, at room temperature. In particular, a series of layered zinc hydroxides, coordinated by aliphatic carboxylate ligands, were produced by the hydrolysis of diethyl zinc and zinc carboxylate mixtures, optimally at a molar ratio of [COOR]/[Zn] = 0.6. Layered zinc hydroxides coordinated by oleate ligands form high concentration solutions of isolated monolayers (3 nm thick x ∼ 26 nm) in apolar organic solvents (up to 23 mg mL-1 in toluene), as confirmed by both atomic force and transmission electron microscopies of deposited species. The high solubility of the product allows the synthetic pathway to be monitored directly in situ through 1H NMR spectroscopy. The high solubility also provides a route to solution deposition of active functional materials, as illustrated by the formation of nanoporous films of optically transparent porous zinc oxide (1 µm thickness) after annealing at 500 °C. This new organometallic route to 2D materials obviates common complications of top-down exfoliation syntheses, including sonochemical-degradation and low yields of aggregated polydispersed layers, and may potentially be extended to a wide range of systems.

Reversible Redox Cycling of Well-Defined, Ultrasmall Cu/Cu2O Nanoparticles.

Exceptionally small and well-defined copper (Cu) and cuprite (Cu2O) nanoparticles (NPs) are synthesized by the reaction of mesitylcopper(I) with either H2 or air, respectively. In the presence of substoichiometric quantities of ligands, namely, stearic or di(octyl)phosphinic acid (0.1-0.2 equiv vs Cu), ultrasmall nanoparticles are prepared with diameters as low as ∼2 nm, soluble in a range of solvents. The solutions of Cu NPs undergo quantitative oxidation, on exposure to air, to form Cu2O NPs. The Cu2O NPs can be reduced back to Cu(0) NPs using accessible temperatures and low pressures of hydrogen (135 °C, 3 bar H2). This striking reversible redox cycling of the discrete, solubilized Cu/Cu(I) colloids was successfully repeated over 10 cycles, representing 19 separate reactions. The ligands influence the evolution of both composition and size of the nanoparticles, during synthesis and redox cycling, as explored in detail using vacuum-transfer aberration-corrected transmission electron microscopy, X-ray photoelectron spectroscopy, and visible spectroscopy.

Organometallic chemistry using partially fluorinated benzenes.

Fluorobenzenes, in particular fluorobenzene (FB) and 1,2-difluorobenzene (1,2-DiFB), are increasingly becoming recognised as versatile solvents for conducting organometallic chemistry and transition-metal-based catalysis. The presence of fluorine substituents reduces the ability to donate π-electron density from the arene and consequently fluorobenzenes generally bind weakly to metal centres, allowing them to be used as essentially non-coordinating solvents or as readily displaced ligands. In this context, examples of well-defined complexes of fluorobenzenes are discussed, including trends in binding strength with increasing fluorination and different substitution patterns. Compared to more highly fluorinated benzenes, FB and 1,2-DiFB typically demonstrate greater chemical inertness, however, C-H and C-F bond activation reactions can be induced using appropriately reactive transition metal complexes. Such reactions are surveyed, including catalytic examples, not only to provide perspective for the use of FB and 1,2-DiFB as innocent solvent media, but also to highlight opportunities for their exploitation in contemporary organic synthesis.

Enhancing the Antibacterial Activity of Light-Activated Surfaces Containing Crystal Violet and ZnO Nanoparticles: Investigation of Nanoparticle Size, Capping Ligand, and Dopants.

Healthcare-associated infections pose a serious risk for patients, staff, and visitors and are a severe burden on the National Health Service, costing at least £1 billion annually. Antimicrobial surfaces significantly contribute toward reducing the incidence of infections as they prevent bacterial adhesion and cause bacterial cell death. Using a simple, easily upscalable swell-encapsulation-shrink method, novel antimicrobial surfaces have been developed by incorporating metal oxide nanoparticles (NPs) and crystal violet (CV) dye into medical-grade polyurethane sheets. This study compares the bactericidal effects of polyurethane incorporating ZnO, Mg-doped ZnO, and MgO. All metal oxide NPs are well defined, with average diameters ranging from 2 to 18 nm. These materials demonstrate potent bactericidal activity when tested against clinically relevant bacteria such as Escherichia coli and Staphylococcus aureus. Additionally, these composites are tested against an epidemic strain of methicillin-resistant Staphylococcus aureus (MRSA) that is rife in hospitals throughout the UK. Furthermore, we have tested these materials using a low light intensity (∼500 lx), similar to that present in many clinical environments. The highest activity is achieved from polymer composites incorporating CV and ∼3 nm ZnO NPs, and the different performances of the metal oxides have been discussed.

Simple phosphinate ligands access zinc clusters identified in the synthesis of zinc oxide nanoparticles.

The bottom-up synthesis of ligand-stabilized functional nanoparticles from molecular precursors is widely applied but is difficult to study mechanistically. Here we use 31P NMR spectroscopy to follow the trajectory of phosphinate ligands during the synthesis of a range of ligated zinc oxo clusters, containing 4, 6 and 11 zinc atoms. Using an organometallic route, the clusters interconvert rapidly and self-assemble in solution based on thermodynamic equilibria rather than nucleation kinetics. These clusters are also identified in situ during the synthesis of phosphinate-capped zinc oxide nanoparticles. Unexpectedly, the ligand is sequestered to a stable Zn11 cluster during the majority of the synthesis and only becomes coordinated to the nanoparticle surface, in the final step. In addition to a versatile and accessible route to (optionally doped) zinc clusters, the findings provide an understanding of the role of well-defined molecular precursors during the synthesis of small (2-4 nm) nanoparticles.

The Simplest Amino-borane H2 B=NH2 Trapped on a Rhodium Dimer: Pre-Catalysts for Amine-Borane Dehydropolymerization.

The µ-amino-borane complexes [Rh2 (L(R) )2 (µ-H)(µ-H2 B=NHR')][BAr(F) 4 ] (L(R) =R2 P(CH2 )3 PR2 ; R=Ph, (i) Pr; R'=H, Me) form by addition of H3 B⋅NMeR'H2 to [Rh(L(R) )(η(6) -C6 H5 F)][BAr(F) 4 ]. DFT calculations demonstrate that the amino-borane interacts with the Rh centers through strong Rh-H and Rh-B interactions. Mechanistic investigations show that these dimers can form by a boronium-mediated route, and are pre-catalysts for amine-borane dehydropolymerization, suggesting a possible role for bimetallic motifs in catalysis.

Well-Defined and Robust Rhodium Catalysts for the Hydroacylation of Terminal and Internal Alkenes.

A Rh-catalyst system based on the asymmetric ligand (t)Bu2PCH2P(o-C6H4OMe)2 is reported that allows for the hydroacylation of challenging internal alkenes with ß-substituted aldehydes. Mechanistic studies point to the stabilizing role of both excess alkene and the OMe-group.

A CH2Cl2 complex of a [Rh(pincer)](+) cation.

The CH2Cl2 complex [Rh((tBu)PONOP)(κ(1)-ClCH2Cl)][BAr(F)4] is reported, that also acts as a useful synthon for other complexes such as N2, CO and H2 adducts; while the analogous PNP complex undergoes C-Cl activation.

Organometallic synthesis, reactivity and catalysis in the solid state using well-defined single-site species.

Acting as a bridge between the heterogeneous and homogeneous realms, the use of discrete, well-defined, solid-state organometallic complexes for synthesis and catalysis is a remarkably undeveloped field. Here, we present a review of this topic, focusing on describing the key transformations that can be observed at a transition-metal centre, as well as the use of well-defined organometallic complexes in the solid state as catalysts. There is a particular focus upon gas-solid reactivity/catalysis and single-crystal-to-single-crystal transformations.