Designed sol–gel precursors for atomically dispersed Nb and Pb within TiO2 as catalysts for dihydroxyacetone transformation

New N-methyldiethanolamine-modified metal alkoxides were synthesized and employed as sol–gel precursors to obtain atomically dispersed catalysts with high surface area and tunable acid–base properties.

Molecular Engineering of Metal Alkoxides for Solution Phase Synthesis of High-Tech Metal Oxide Nanomaterials

The 'bottom-up' synthesis of inorganic nanomaterials with precision at the atomic/molecular level offers many opportunities for the design and improvement of the nanomaterials for various applications. Molecular engineering during soft chemical processing for the synthesis of functional nanomaterials enables the desired chemical and physical properties of the precursors, such as solubility or volatility, clean decomposition, control of stoichiometry for multimetallic species to name a few, and leads to easy control of uniform particle size distribution, stoichiometry…. This Minireview illustrates some important aspects of the molecular engineering in light of some recent developments from the molecular synthesis of nanomaterials involving non-silicon metal alkoxide systems for high-tech applications.

Heteroleptic Tin(IV) Aminoalkoxides and Aminofluoroalkoxides as MOCVD Precursors for Undoped and F-Doped SnO2 Thin Films

A series of asymmetric and potentially bidentate amino alcohols and amino fluoro alcohols (R_NOH) having a different number of methyl/trifluoromethyl substituents at the α-carbon atom, [HOC(R¹)(R²)CH₂NMe₂] (R¹ = R² = H (dmaeH); R¹ = H, R² = CH₃ (dmapH); R¹ = R² = CH₃ (dmampH); R¹ = H, R² = CF₃ (F-dmapH); R¹ = R² = CF₃ (F-dmampH)) have been used to develop new monomeric and heteroleptic tin(IV) amino(fluoro)alkoxides [Sn(OR)₂(OR_N)₂] (R = Et, Prⁱ, Bu^t). These new complexes, which were thoroughly characterized by spectroscopy (IR and multinuclei NMR (¹H, ¹³C, ¹⁹F, and ¹¹⁹Sn)) as well as single-crystal X-ray studies on representative samples, were investigated for their thermal behavior to determine their suitability as MOCVD precursors for the deposition of metal oxide thin films. The two most suitable compounds, [Sn(OBu^t)₂(dmamp)₂] and [Sn(OBu^t)₂(F-dmamp)₂], were used in a direct liquid injection chemical vapor deposition (DLI-CVD) process to deposit undoped SnO₂ and F-doped SnO₂ thin films, respectively, on silicon and quartz substrates. Film growth rates at different temperatures (from 400 to 700 °C), film thickness, crystalline quality, and surface morphology were investigated. The films deposited on quartz showed high transparency (above 80%) in the visible region and low carbon contamination on the surface (11-13% from XPS), which could easily be removed completely with 2 min of Ar⁺ sputtering.

Room-temperature conversion of Cu2−xSe to CuAgSe nanoparticles to enhance the photocatalytic performance of their composites with TiO2

Surfactant-free CuAgSe–TiO₂ composites show an improved photocatalysis as compared to Cu_2−xSe–TiO₂ composites or TiO₂ alone.

Nanometric NaYF4 as an Unconventional Support for Gold Catalysts for Oxidation Reactions

The metal-support interaction plays an important role in gold catalysis. We employ here crystalline cubic (α-) and hexagonal (β-) phases of heterometallic fluoride NaYF₄ nanoparticles (NPs), obtained by the decomposition of a single source precursor [NaY(TFA)₄(diglyme)] (TFA = trifluoroacetate), as nonoxide supports for gold catalysts. Using an isostructural gadolinium analogue, we also obtained doped α-NaYF₄:Gd³⁺ and β-NaYF₄:Gd³⁺ NPs. A successful deposition of ∼1% by weight gold NPs of average size 5-6.5 nm on these doped and undoped metal fluorides using HAuCl₄·3H₂O afforded Au/NaYF₄ catalysts which were thoroughly characterized by using several physicochemical techniques such as X-ray diffraction, Brunauer-Emmett-Teller analysis, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. A comparative study of the above catalysts for different oxidation reactions show that while for the aerobic oxidation of trans-stilbene in solution phase, they are either better (in terms of stilbene conversion) or at par (in terms of trans-stilbene oxide yield) in comparison to the reference catalyst Au/TiO₂ of the World Gold Council, their activity toward CO oxidation reactions in gas phase remains much less than that of gold catalysts supported on metal oxides.

Chiroptical and magnetic properties of star-shaped Fe complexes from chiral Schiff bases. Structural and magnetic correlations based on continuous shape measures

New chiral FeIII4 star-shaped complexes have been synthesized starting from enantiomerically pure Schiff bases and chiroptically and magnetically characterized. The structural and magnetic properties of the complete family of 40 Fe4 complexes reported in the literature have been analyzed in the search for synthetic and magnetostructural correlations.

Precursor-mediated synthesis of Cu2−xSe nanoparticles and their composites with TiO2 for improved photocatalysis

Simple, but effective. Successful isolation and characterization of an intermediate during the reaction of ^tBu₂Se with Cu(TFA)₂ establishes the route for the formation of copper selenide NPs and Cu_2−xSe–TiO₂ composites as active photocatalysts.

Asymmetrically substituted triazenes as poor electron donor ligands in the precursor chemistry of iron(ii) for iron-based metallic and intermetallic nanocrystals

First as precursors: Heteroleptic Fe^II complexes derived from new asymmetric triazene ligands t-BuNN-NHR (R = Et, i-Pr, n-Bu) show interesting molecular and precursor chemistry.

Photochemical solution processing of films of metastable phases for flexible devices: the β-Bi2O3 polymorph

The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi₂O₃ polymorph. The pure β-Bi₂O₃ phase is thermodynamically stable at high temperature (450-667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a -Bi-O-Bi- continuous network in the deposited layers and the further conversion into the β-Bi₂O₃ polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi₂O₃ films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi₂O₃ films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases.