Comparing conventional and microwave-assisted heating in PET degradation mediated by imidazolium-based halometallate complexes

The catalytic activity of two halometallate complexes based on imidazolium cations, (dimim)[FeCl4] (1) and (dimim)2[Fe2Cl6(μ-O)] (2), was evaluated in the glycolysis of polyethylene terephthalate (PET), either under conventional heating or microwave-assisted conditions. The two procedures led to the formation of bis(2-hydroxyethyl)terephthalate (BHET) as the major product with high yields, also allowing the isolation and structural characterization of a new polymorph. The influence of the halometallate structure on the catalytic activity was investigated, and additional experimental studies proved the involvement of both the imidazolium cation and metal anion in the reaction mechanism. The comparison of both approaches showed the advantages of the microwave methodology in terms of efficiency and time saving. Indeed, the use of ground PET and microwave heating provided quantitative yields of BHET. Under conventional heating conditions, the dinuclear iron complex gave a slightly lower yield than (dimim)[FeCl4] (74% vs. 77% for post-consumer PET) after 24 h of reaction. However, the microwave-assisted process led to comparable results in remarkably shorter reaction times (2 h). Interestingly, complex 2, containing the dipolar [Fe2Cl6(μ-O)]2− moiety, provided higher yields than 1 with the non-dipolar [FeCl4]− anion (77% vs. 69%). This behaviour has been rationalized on the basis of dielectric heating mechanisms (polarization and conduction), and it suggests a new approach towards obtaining more efficient catalysts by tailoring the catalytic species to be active in both heating mechanisms.Financial support from the Spanish Ministerio de Ciencia e Innovación (Projects MAT2014-55049-C2-R and MAT2016-75883-C2-1-P), Universidad del País Vasco/EuskalHerrikoUnibertsitatea (GIU17/50 and PPG17/37). Universidad de Cantabria (Proyecto Puente convocatoria 2018 financed by SODERCAN-FEDER)

An Oxalate Bridged Binuclear Iron(III) Ionic Liquid for the Highly Efficient Glycolysis of Polyethylene Terephthalate under Microwave Irradiation

An oxalate-bridged binuclear iron(III) ionic liquid combined with an imidazolium based cation, (dimim)2[Fe2Cl4(µ-ox)], was synthesized and characterized by a wide range of techniques. This halometallate ionic liquid was active in catalyzing the depolymerization of polyethylene terephthalate (PET) by glycolysis, under conventional and microwave-assisted heating conditions. Both methodologies were very selective towards the production of bis(2-hydroxyethyl)terephthalate (BHET). The employment of microwave heating proved beneficial in terms of time and energy saving when compared to the use of thermal heating. Indeed, dielectric spectroscopy studies revealed that the binuclear iron-containing ionic liquid exhibits an excellent heating response under an electromagnetic field. The catalyst provided quantitative conversions to BHET in the glycolysis of post-consumer PET bottles in only 3 h through microwave heating, as compared to 80 % conversion after 24 h under conventional heating

Neutron Powder Diffraction study of the Magnetic Ionic Liquid Emim[FeCL4] and its deuterated phase

A magnetic ionic liquid comprising 1-ethyl-3 methylimidazolium (Emim) cations and tetraclhoroferrate(III) (FeCl4) anions and its deuterated phase were synthetized and characterized magnetically. In both materials, the low temperature dependence of the magnetic susceptibility presents a maximum (around 4 K) related to an antiferromagnetic ordering, but the ordering temperatures are slightly shifted and the curves display different shapes. In addition, the magnetization of the deuterated phase tends to saturate at higher values than that corresponding to the non-deuterated analogue. A comparison of the neutron diffraction patterns above and below the magnetic transition clearly shows that the crystal and magnetic structures of these materials are different. Therefore, the present findings clearly prove that the magnetic exchange interactions that induce three-dimensional magnetic ordering are modified after the deuteration process.Part of this work was carried out at Institute Laue-Langevin (ILL) of Grenoble and was partially financially supported by MEC research project MAT2011-27573-C04

Pressure-induced charge ordering transition in CaMn7O12

We use high-pressure resistivity and single crystal x-ray diffraction at ambient and low temperature to investigate the charge ordering phase transition of CaMn 7 O 12 . We have found that at ambient temperature the Jahn-Teller distortion of the Mn 3 + O 6 octahedra rapidly decreases above 20 GPa, and vanishes at 28 GPa, when two Mn octahedral sites initially occupied by Mn 3 + and Mn 4 + become regular and equivalent as the result of a charge delocalization. Such a change correlates with a two orders of magnitude drop in the resistivity and a symmetry increase from the low-pressure rhombohedral R ¯ 3 phase to the cubic Im ¯ 3 structure, the same as one found at ambient pressure above 440 K. This yields the slope of the charge ordering phase boundary of d T c / d p ? ? 6 K/GPa. This result is further supported by the lack of a structural phase transition up to the maximum measured pressure of 30 GPa when the experiment is performed at 70 K. The satellite reflections of the structural modulation of the multiferroic phase of CaMn 7 O 12 observed at 70 K were found to hold up to 25 GPa with the structure keeping a constant modulation vector k = ( 0 0 0.925 ) with pressure. The average structure at 70 K does not show other indications of further phase transition.Y. Li and X. Du from Peking University are greatly acknowledged for growing and providing the CaMn7O12 crystals. D. Spahr and J. König from Goethe University are acknowledged for help with the single-crystal diffraction experiments. M.S. would like to acknowledge the financial support under the DFG-ANR Grant No. WI1232/41-1 and DFG GACR Project No. WI3320/3-1. V.M. and J.R.-F. thank the financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN) for the Beatriz Galindo Program (BG20/000777) and for the Project No. PGC2018-097520- A-I00, respectively. DESY Photon Science is gratefully acknowledged. PETRA III at DESY is a member of the Helmholtz Association (HGF)

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)

Magnetovolume and magnetocaloric effects in Er2Fe17

Combining different experimental techniques, investigations in hexagonal P63/mmc Er2Fe17 show remarkable magnetovolume anomalies below the Curie temperature, TC. The spontaneous magnetostriction reaches 1.6×10−2 at 5 K and falls to zero well above TC, owing to short-range magnetic correlations. Moreover, Er2Fe17 exhibits direct and inverse magnetocaloric effects (MCE) with moderate isothermal magnetic entropy ΔSM, and diabatic temperature ΔTad changes [ΔSM∼−4.7 J(kgK)−1 and ΔTad∼2.5 K near the TC, and ΔSM∼1.3 J(kgK)−1 and ΔTad∼−0.6 K at 40 K for ΔH=80 kOe, respectively, determined from magnetization measurements]. The existence of an inverse MCE seems to be related to a crystalline electric field-level crossover in the Er sublattice and the ferrimagnetic arrangement between the magnetic moments of the Er and Fe sublattice. The main trends found experimentally for the temperature dependence of ΔSM and ΔTad as well as for the atomic magnetic moments are qualitatively well described considering a mean-field Hamiltonian that incorporates both crystalline electric field and exchange interactions. ΔSM(T) and ΔTad(T) curves are essentially zero at ∼150 K, the temperature where the transition from direct to inverse MCE occurs. A possible interplay between the MCE and the magnetovolume anomalies is also discussed.Financial support from Spanish MICINN (MAT2011-27573-C04-02) and from the Basque Government (IT-347- 07) is acknowledged. J.L.S.Ll. acknowledges the support received from CONACYT, Mexico, under the project CB2010-01-156932, and Laboratorio Nacional de Investigaciones en Nanociencias y Nanotecnología (LINAN, IPICyT). J.A.R.V. acknowledges the support from the research project MAT2007-61621. We thank ILL and CRG-D1B for allocating neutron beamtime, and ESRF for synchrotron beamtime. The SCTs at the University of Oviedo and the technical support received from M.Sc. G. J. Labrada-Delgado and B. A. Rivera-Escoto (DMA, IPICyT) are also acknowledged

An in solution adsorption characterization technique based on the response to an external magnetic field of porous paramagnetic materials: application on supramolecular metal–adenine frameworks containing heterometallic heptameric clusters

Herein we explore the opportunities arising from combining magnetic properties and porosity in metal–organic materials. In this sense, we have prepared an adenine based homometallic wheel-shaped heptameric [Cu7(μ-adeninato)6(μ3-OH)6(μ-OH2)4]2+ entity containing two metal coordination environments: CuO6 at the core of the wheel with an unusually modest Jahn–Teller distortion and six peripheral CuN2O4 with a more pronounced elongation. The difference in the coordination environments of this compound facilitates the selective replacement of the central metal position by other metal centers (ZnII, NiII, CoII and CrIII) and boosts the magnetic properties of the homometallic heptameric entity. The nature of the central metal modulates the complex net of ferro- and antiferromagnetic superexchange pathways within the heptameric entity to tune the total spin (ST = 3 (Cu6Zn), 5/2 (Cu6Cu), 2 (Cu6Ni), 3/2 (Cu6Co), and 9/2 (Cu6Cr)). No evidence of single-molecule magnet behavior has been observed at 2 K, but at room temperature, where these compounds are still in the paramagnetic regime, the attraction force exerted by an external magnetic field (H) on particles immersed in a liquid is enough to keep them attached to an electromagnet pole. The 4S(S + 1) value of the central metal follows a linear dependence with respect to the 1/[H·∇(H)] value at which the particles are detached from the pole of the electromagnet. There is also a linear dependence of the H·∇(H) term with respect to the adsorbate mass incorporated inside the pores of the paramagnetic adsorbent which has allowed performing straightforward sorption selectivity experiments on Cu6Cu directly in solution, which are based on a property of the adsorbent and not as usually based on an indirect assessment of the adsorbate remaining in solution.Eusko Jaurlaritza/Gobierno Vasco (IT1291-19; IT1722-22; ELKARTEK program KK-2022/00032), Ministerio de Universidades and the European Union-Next Generation EU (marsa21/52, R. P. A.), Ministerio de Ciencia e Innovación (PID2019-108028GB-C21). SGIker (UPV/EHU, MICINN, GV/EJ, ESF). ELKARTEK program KK-2022/0003

((R)-( )-3-Hydroxyquinuclidium)[FeCl4]; a plastic hybrid compound with chirality, ferroelectricity and long range magnetic ordering

Quinuclidinium salts and their derivatives are now in the focus of materials science as building units of multifunctional materials. Their properties can be easily switchable, allowing their use in a wide range of physical applications. One type of these kinds of materials, the homochiral hybrid halometallate ferroelectric compounds, is not well understood. In this work, (R)-( )-3-quinuclidinol hydrochloride was used in the synthesis of ((R)-( )-3-hydroxyquinuclidium)[FeCl4]. The use of this enantiomeric cation forces crystallographic non-centrosymmetry, which was confirmed by polarimetry and circular dichroism spectroscopy. We studied the physical properties of this compound at different temperatures by single crystal, synchrotron and neutron powder X-ray diffraction, which showed a rich series of structural and magnetic phase transitions. From synchrotron powder X-ray diffraction data, a plastic phase was observed above 370 K (phase I). Between 370 K and ca. 310 K, an intermediate polar phase was detected, solved in a non-centrosymmetric polar space group (C2) (phase II). Below ca. 310 K, the compound crystallizes in the triclinic P1 non-centrosymmetric space group (phase III) which is maintained down to 4 K, followed by phase IV, which shows tridimensional magnetic ordering. The temperature evolution of the neutron diffraction data shows the appearance of new reflections below 4 K. These reflections can be indexed to a commensurate propagation vector k = (0, 0, 12). The magnetic structure below TN was solved in the Ps1 Shubnikov space group, which gives rise to an antiferromagnetic structure, compatible with the magnetometry measurements. Near room temperature, the crystal phase transition is associated with a dielectric change. In particular, the phase transition between phase III (S.G.:P1) and phase II (S.G.:C2) involves an increase of symmetry between two non-centrosymmetric space groups. Therefore, it allows, by symmetry, the emergence of ferroelectric and ferroelastic ordering. Piezoresponse force microscopy (PFM) imaging measurements provided evidence for polarization switching and a local ferroelectric behavior of phase III at room temperature. Additionally, the obtained butterfly curve and hysteresis loop by PFM exhibits a low coercive voltage of B10 V. This value is remarkable, since it approaches those obtained for materials with application in ferroelectric random access memories (FeRAMs).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, MAT2017-83631-C3-3-R, MAT2017-86453-R, PGC2018-097520-A-100 and PID2019-104050RAI00) is acknowledged. The authors gratefully acknowledge the technical and human support provided by SGIKer (UPV/EHU, MINECO, GV/EJ, ERDF, and ESF). Carmen Martín is grateful to VI PPIT-2018 from Universidad de Sevilla. The paper is (partly) based on the results of experiments carried out at the ALBA Synchrotron Light Source in Barcelona (proposal 2019083666) and Institute Laue-Langevin (ILL) of Grenoble (Proposals 5-31-2580 and 5-31-2460)

Synthesis, microstructure and volumetry of novel metal thiocyanate ionic liquids with [BMIM] cation

We present a new family of ionic liquids (ILs) with a common cation, 1-butyl-3-methyl imidazolium, the popular [BMIM]+ (also written C4C1Im+) and a variety of anionic complexes (also called adducts) based in thiocyanate (SCN)?: one blank compound, BMIM(SCN), and ten doped with metals having different oxidation states: Al+3, Mn+2, Fe+3, Cr+3, Ni+2, Hg+2, Zn+2, Co+2, Cd+2 and Cu+, forming, respectively, [BMIM]3[Al(SCN)6], [BMIM]4 Mn(SCN)6, [BMIM]3 Fe(SCN)6, [BMIM]3 Cr(SCN)6, [BMIM]4 Ni(SCN)6, [BMIM]2 Hg(SCN)4, [BMIM]2 Zn(SCN)4, [BMIM]2 Co(SCN)4, [BMIM]2 Cd(SCN)4 and [BMIM]3 Cu(SCN)4. All of them were synthesized by us, except the blank IL and the Co thiocyanate, which are commercial. Obtained products have been characterized by NMR, and also by electrospray ionization, MS-ES, which allows the determination of the new ILs purities. Then, compounds have been analyzed using FT-IR and Raman spectroscopy. In addition, magnetic susceptibility and refractive index measurements were performed in some of the compounds studied, as well as thermal characterization using DSC and TGA. Finally, experimental measurements of density on all those ILs have been performed, and for some of the samples in a broad temperature range (about 100 K). In spite of being very similar compounds from the chemical point of view, they present quite different physical properties, including optical, thermal and magnetic ones? Also, they show different oxidation states (one with +1, six with +2 and other three with +3). We guess that this family of ILs will have interesting applications, mainly for photonic devices

The origin of pottery technology in Asturias: the contribution of the site of Los Canes (Arangas, Cabrales)

Resumen: La aparicion de la tecnologia ceramica en la region cantabrica se produce en la primera mitad del V milenio cal BC. A pesar de lo bien establecida que se encuentra su cronologia, es escasa la informacion referente a sus rasgos tecnologicos, morfológicos y decorativos. En este articulo se presenta el estudio de la ceramica procedente de la UE 7 del yacimiento de Los Canes, que constituye el conjunto ceramico mas antiguo documentado en la zona asturiana. En su analisis se ha conjugado la caracterización macroscopica y el analisis tecnologico mediante la aplicacion de diversas técnicas mineralogicas (petrografia y difraccion de rayos X) y geoquimicas (EDS de secciones pulidas). Los resultados del estudio reflejan una coherencia entre el entorno geológico en el que se encuentra el yacimiento y las materias primas empleadas en la manufactura ceramica. Ademas, se ha podido discriminar la preparacion previa de la pasta ceramica mediante la adicion de desgrasante. La escasa informacion morfologica y decorativa no permite analizar la relacion entre las distintas elecciones tecnológicas y las formas de los recipientesAbstract: The origin of pottery technology in the Cantabrian region is dated in the first half of the fifth millennium cal BC. Although its chronology is well established, information about the technological, morphological and decorative features is scarce. The pottery recorded in SU 7 at the site of Los Canes Cave constitutes the oldest know ceramic ensemble documented in the Asturian area. Its study is based on macroscopic characterization and technological analysis through the application of different mineralogical (petrography and X-Ray Diffraction) and geochemical techniques (SEM-EDS). The results indicate consistency between the geological area surroundings of the site and the raw materials used in the manufacturing process. Furthermore, it was possible to distinguish a previous preparation of the clay, with the addition of temper. The scare information about the morphology and decoration do not allow an analysis of the relationship between the different technological choices and the morphology of the pots