Regioselective Formation of 2,5-Disubstituted Oxazoles Via Copper(I)-Catalyzed Cycloaddition of Acyl Azides and 1-Alkynes

The reaction of 1-alkynes with acylazides in the presence of [Tpm*,BrCu(NCMe)]BF4 (Tpm*,Br = tris(3,5-dimethyl-4-bromopyrazolyl)methane) as the catalyst provides 2,5-oxazoles in moderate to high yields. This is a novel transformation of CuAAC type, that constitutes a significant variation of the commonly observed [3+2] cycloaddition reaction to yield 1,2,3-triazolesMEC (Proyecto CTQ2008-00042/BQU, Consolider Ingenio 2010, Grant No. CSD2006-003) and the Junta de Andalucía (Proyecto P07-FQM-02745).This work is dedicated to Prof. Jose Barluenga on the occasion of his retirement. This research was financially supported by MEC (Proyecto CTQ2008-00042/BQU, Consolider Ingenio 2010, Grant CSD2006-003) and the Junta de Andalucia (Proyecto P07-FQM-02745). I.C. thanks MEC for a research fellowship. We gratefully acknowledge Prof. Antonio Echavarren for helpful discussions. Dr. Ana Caballero and Dr. Tomas R. Belderrain are thanked for assistance with GC MS and NMR studies

A comparative study on luminescence properties of Y2O3: Pr3+ nanocrystals prepared by different synthesis methods

Pr3+-doped Y2O3 nanocrystals (NCs) have been obtained via five wet-chemistry synthesis methods which were optimized in order to achieve superior optical properties. To this end, a systematic study on the influence of different reaction parameters was performed for each procedure. Specifically, precursor concentration, reaction temperature, calcination temperature, and time, among others, were analyzed. The synthesized Y2O3: Pr3+ NCs were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and reflectance and Raman spectroscopy. In addition, the optical properties of such NCs were investigated by excitation, emission, and luminescence decay measurements. Concretely, emission from the 1D2 level was detected in all samples, while emission from 3PJ was absent. Finally, the effect of the synthesis methods and the reaction conditions on the luminescence decay has been discussed, and a comparative study of the different methods using the fluorescence lifetime of so-obtained Y2O3: Pr3+ NCs as a figure of merit has been carried out.This work was funded with a Future and Emerging Technologies (FET) NCLas project; European Union; Proposal: 829161

Incommensurate crystal structure, thermal expansion study and magnetic properties of (dimethylimidazolium)2[Fe2Cl6(?-O)]

A thorough characterization of the title compound, (dimim)2[Fe2Cl6(µ-O)], consisting of a (µ-oxido)-bridged binuclear iron(III) complex and 1,3-dimethylimiazolium (dimim) cation, has been performed using a wide range of techniques. The room temperature disordered crystal structure of this compound transits to an incommensurately modulated crystal structure at 100 K; to our knowledge, the first one found for an imidazolium halometallate complex. The crystal structure was solved in the superspace group PĪ(/α/β/γ)0 with modulation vector q=0.1370(10) 0.0982(10) 0.326(2) at 100 K. Variable temperature synchrotron powder x-ray diffraction showed the presence of satellite peaks in addition to the main diffraction peaks up to 208 K. Furthermore, a thermal expansion study was performed with this technique from 100 to 383 K (near of its melting point) adressing questions about the nature and consequences of the ion self-assembly of this (µ-oxido)-bridged binuclear iron(III) complex, as well as the molecular motion of the imidazolium cation within the crystalline structure as a response to the temperature effect. Finally, we present a deep magnetic study based on magnetic susceptibility, magnetization and Mössbauer measurements, where the strong antiferromagnetic exchange coupling detected is due to the occurrence of a µ-oxido bridge between the Fe(III), giving rise to an intra-dimeric antiferromagnetic exchange coupling of -308 cm-1.Financial support from Universidad de Cantabria (Proyecto Puente convocatoria 2018 funded by SODERCAN_FEDER) , Universidad del País Vasco/Euskal Herriko Unibertsitatea (GIU17/50 and PPG17/37) and Ministerio de Economia y Competividad (MAT2017-89239-C2-(1,2)-P)

Glass powder doping of nanocrystal-doped fibres: challenges and results

Incorporating new optical materials as nanocrystals into glass fibres for new functionalities has recently become a hot research topic. Our team (funded by the European FET Open project NCLAS) investigates the introduction of nanoscale laser crystallites into the core of optical fibres using the glass powder doping method. Active Y2O3:Pr3+ nanocrystals (NCs) were prepared via different synthesis methods, and structurally and spectroscopically characterized. After modification of technological parameters, the optimised NCs have been proposed as a luminescence centres to embed into germanate and silicate glass hosts. Glasses were analysed in terms of optical (transmission, refractive index matching to NCs) and thermal (thermal stability, viscosity, thermal expansion coefficient) parameters. Crystallisation issues during fibre drawing were particularly investigated. In a first step, glass powder-NCs mixing techniques and fibre preform preparation were developed. It was shown that temperature cycle profiles including dwell time and heating/cooling ramp rates influenced the glass-NCs properties and can lead to glass crystallisation or NCs dissolution. The sintering investigations pointed out the melting temperature limits to preserve active NCs in the glasses. In germanate glasses, Y2O3:Pr3+ dissolution was noticed at 800°C. In the case of the silicate glass compositions these regions vary from 700°C to 1050°C. The results allowed to select optical fibre drawing conditions performed by the powder-in-tube method. Their distribution uniformity is not yet sufficient, requiring further optimisation of the drawing kinetics.The research project funded by the European FET Open project NCLas: NanoCrystals in Fibre Lasers, Grant agreement number: 82916

Pr3+-doped Y2O3 nanocrystals embedded in Y2O3 thin films as a sandwich-like structure prepared by pulsed laser deposition

Pr3+-doped yttria (Y2O3) nanocrystal layers embedded in between pure yttria thin films were prepared on four different substrates. Pulsed laser deposition was used to fabricate this sandwich-like structure. An exhaustive structural and optical characterization of the initial nanocrystals was performed to study their preservation once incorporated between the deposited thin films. We demonstrate that the prepared Y2O3:Pr3+ nanocrystals can be integrated into the thin films after the pulsed laser deposition process, retaining their original crystal structure and luminescent features regardless of the number of deposition cycles and the nature of the substrate. In this sense, we present a novel method to embed and protect the luminescent material, paving the way for developing future optoelectronic applications.The authors acknowledge financial support from the European Community through a Future and Emerging Technologies (FET) project NCLas (Proposal: 829161)

Photocatalytic activity of undoped and Mn- and Co-doped TiO2 nanocrystals incorporated in enamel coatings on stainless steel

A series of undoped and transition-metal (TM)-doped TiO2 nanocrystals (NCs) were synthesized and calcined at different temperatures, and fully characterized. Such NCs were employed as catalysts for the photodegradation of methylene blue, which enabled us to study the influence of both NC size and anatase/brookite/rutile phase ratio on the photocatalytic activity, as well as the effect of different TM dopants, namely Mn and Co. Then, the NCs were used as active additives for the fabrication of a new photocatalytic system composed of an enamel incorporating these NCs supported onto a stainless-steel sheet. NCs both in powder form and incorporated in enamels deposited on steel were characterized by transmission electron microscopy, X-ray diffraction, and reflectance and Raman spectroscopy. We demonstrate how the calcination of TiO2 NCs induces both a growth in the anatase ratio and formation of the rutile form, which leads to a photocatalytic activity increase. Similarly, doping with Mn and Co gives rise to an enhancement of the catalytic performance attributed to a displacement of the energy bandgap. The obtained material combines the resistance of steel and the photocatalytic activity of TiO2 deposited on enamel, which also operates as a corrosion protection layer for the former. The resulting smart photocatalytic surface presents many applications such as a self-cleaning coating and potential use for NOx photodegradation.The authors acknowledge financial support from company VITRISPAN S.A. M.T.C. would like to thank University of Cantabria and the Government of Cantabria for her pre-doctoral grant “Concepción Arenal”

Paramagnetic ionic liquid-coated SiO2@Fe3O4 nanoparticles - The next generation of magnetically recoverable nanocatalysts applied in the glycolysis of PET

The functionalization of silica-coated, magnetic Fe3O4 nanoparticles, with an iron-containing ionic liquid, allows for the synthesis of a Fe3O4@SiO2@(mim)[FeCl4] system that can be employed as a magnetically recoverable nanocatalyst. Herein, we present the use of Fe3O4@SiO2@(mim)[FeCl4] for the glycolysis of PET into BHET under conventional heating. The catalyst achieved nearly 100% yield and selectivity over twelve consecutive reaction cycles at 180 °C and was efficiently recovered without tedious work-up or purification processes. Additional analyses revealed that the amount of catalyst lost after each cycle was negligible and no trace of Fe was found in the purified BHET product.Financial support from Universidad de Cantabria (Proyecto Puente convocatoria 2018 financed by SODERCAN_FEDER) and Spanish Ministry of Economy Industry and Competitiveness (Grant No.CTQ2017-83175R)

Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts

Ligand control of metal nanoparticles (MNPs) is rapidly gaining importance as ligands can stabilize the MNPs and regulate their catalytic properties. Herein we report the first example of Pt NPs ligated by imidazoliumamidinate ligands that bind strongly through the amidinate anion to the platinum surface atoms. The binding was established by 15N NMR spectroscopy, a precedent for nitrogen ligands on MNPs, and XPS. Both monodentate and bidentate coordination modes were found. DFT showed a high bonding energy of up to 48 kcal mol 1 for bidentate bonding to two adjacent metal atoms, which decreased to 28 4 kcal mol 1 for monodentate bonding in the absence of impediments by other ligands. While the surface is densely covered with ligands, both IR and 13C MAS NMR spectra proved the adsorption of CO on the surface and thus the availability of sites for catalysis. A particle size dependent Knight shift was observed in the 13C MAS NMR spectra for the atoms that coordinate to the surface, but for small particles, 1.2 nm, it almost vanished, as theory for MNPs predicts; this had not been experimentally verified before. The Pt NPs were found to be catalysts for the hydrogenation of ketones and a notable ligand effect was observed in the hydrogenation of electron-poor carbonyl groups. The catalytic activity is influenced by remote electron donor/acceptor groups introduced in the aryl-N-substituents of the amidinates; p-anisyl groups on the ligand gave catalysts several times faster the ligand containing p-chlorophenyl groupsMinisterio de Economía, Industria y Competitividad CTQ2015-68978-PPCs CALcul en MIdi-Pyrénées CALMIP-HYPERION P061Equipement National de Calcul Intensif GENCI-TGCC, A001081016

Visible light active Ce-doped and Cu-Ce co-doped TiO2 nanocrystals and optofluidics for clean alcohol production from CO2

Considering CO2 as an alternative and sustainable resource, rather than as a waste to be treated, this work proposes the combination of doped TiO2 nanocrystals with optofluidics for the continuous photoreduction of CO2 to alcohols under ultraviolet and visible light. This approach aims at overcoming one of the major limitations of this technology, namely, current photoreactor configurations and low activity under visible light of the up-to-date photocatalysts. Ce-doped and Cu–Ce-codoped TiO2 nanocrystals, synthesized by a simple and green hydrothermal method with different Cu and Ce contents, are used in a planar optofluidic microreactor with an enhanced surface-area-to-volume ratio, uniform light distribution, and a larger photon receiving area. The results show promising alcohol production rates when doping the photoactive TiO2 nanocrystals with Ce, which leads to a maximum rate of 116 μmol·g–1·h–1 for ethanol and 106 μmol·g–1·h–1 for methanol, exceeding most of the reported values for visible-light-driven CO2 photoreduction to alcohol systems. It is worth noting that the system remains pseudostable for up to 6 h of continuous operation. Altogether, this work provides novel insights into the development of innovative systems for the transformation of CO2 to alcohols under sunlight irradiation.The authors gratefully acknowledge the financial support from Ministerio de Ciencia e Innovación (MCIN) and Spanish State Research Agency (AEI) through the research projects PID2019-104050RA-I00 and TED2021-129810B-C21 funded by MCIN/AEI/10.13039/501100011033

La ciencia y tecnología químicas al servicio de la sociedad: actividad formativa para los alumnos del Máster en Ciencia y Tecnología Químicas

Depto. de Química FísicaFac. de Ciencias QuímicasFALSEsubmitte