17 research outputs found

    I.amAble: la ciencia (química) al alcance de toda la sociedad

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    En este proyecto de innovación, que nace con vocación de continuar en años sucesivos, se persigue mejorar la calidad de la formación de los estudiantes de la Facultad de Ciencias Químicas (F. CC.QQ.) en el ámbito de la docencia teórico-práctica y de la divulgación científica. El trabajo ha consistido en la preparación de unos experimentos prácticos para llevarlos a cabo en centros educativos no universitarios en los que se ha tenido en cuenta la participación conjunta de personas con y sin diversidad funcional, desde una perspectiva inclusiva colaborativa. Estas actividades las han realizado los estudiantes bajo la supervisión de profesores (PDI) y personal de administración y servicios (PAS). Los experimentos se han recogido en fichas didácticas para facilitar su desarrollo y aplicación por parte de otros usuarios. En estas fichas se explica detalladamente cómo realizar las experiencias en formato de taller. Las fichas de los talleres realizados están disponibles en una página web vinculada a la Universidad Complutense bajo el título I.amAble (iamable.ucm.es). Está página ha sido construida por un estudiante de la Facultad de Informática , bajo la supervisión de profesionales, tanto de esa facultad como del Instituto de Tecnología del Conocimiento, y está abierta a contribuciones similares de otras facultades y otras instituciones. La página web está diseñada de manera que resulte lo más intuitiva y accesible posible para todo tipo de público. Entre todos los experimentos se han elegido cuatro para llevarlos a la práctica en centros educativos como actividades inclusivas en las que han participado conjuntamente personas con y sin discapacidad. Con este proyecto se pretende mejorar la calidad docente al ofrecer a los estudiantes la posibilidad de aprender enseñando mediante una actividad semipresencial. El desarrollo por parte de los estudiantes de competencias transversales en educación y en divulgación de la ciencia facilitarán algunas salidas profesionales en el ámbito educativo formal (centros de enseñanza) o informal (museos, animación sociocultural). Otro aspecto importante a resaltar es la potenciación de la colaboración entre todos los miembros de la institución universitaria. Este proyecto pretende contribuir a la mejora de la cultura científica, así como al establecimiento de puentes entre la UCM y la sociedad a la que debe servir. Finalmente, es importante subrayar que incidirá en la inclusión de las personas con discapacidad como parte de la sociedad, a través del acercamiento compartido a la ciencia (Dimensiones de inclusión social y derechos de Schalock; NAVAS MACHO, P. y otros, 2012. Derechos de las personas con discapacidad intelectual: implicaciones de la Convención de Naciones Unidas. Siglo Cero. 43 (243): 7-28.)

    Chirality determination in crystals

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    This tutorial review article discusses chirality determination in the solid state, both in single crystals and in crystal assemblies, with an emphasis on X-ray diffraction. The main principles of using X-ray diffraction to reliably determine absolute structure are summarized, and the complexity which can be encountered in chiral structureskryptoracemates, scalemates and inversion twinningis illustrated with examples from our laboratories and the literature. We then address the problem of the bulk crystallization and discuss different techniques to determine chirality in a large assembly of crystal structures, with a special prominence given to an X-ray natural circular dichroism mapping technique that we recently reported

    Resolution, structures, and vibrational circular dichroism of helicoidal trinickel and tricobalt paddlewheel complexes

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    It has been recently shown that enantiomers of the helicoidal paddlewheel complex [Co3(dpa)4(CH3CN)2]2+ (dpa = the anion of 2,2′‐dipyridylamine) can be resolved using the chiral [As2(tartrate)2]2− anion (AsT) and that these complexes demonstrate a strong chiroptical response in the ultraviolet‐visible and X‐ray energy regions. Here we report that the nickel congener, [Ni3(dpa)4(CH3CN)2]2+, can likewise be resolved using AsT. Depending on the stereochemistry of the enantiopure AsT anion, one or the other of the trinickel enantiomers crystallize from CH3CN and diethyl ether in space group P4212 as the (NBu4)2[Ni3(dpa)4(CH3CN)2](AsT)2·[solvent] salt. After resolution, the AsT salts were converted into the PF6− salts by anion exchange, with retention of the chirality of the trinickel complex. The enantiopure [Ni3(dpa)4(CH3CN)2](PF6)2·2CH3CN and [Co3(dpa)4(CH3CN)2](PF6)2·CH3CN·C4H10O compounds crystallize in space groups C2 and P21, respectively. Both the Ni(II) and Co(II) complex cations are stable towards racemization in CH3CN. Vibrational circular dichroism (VCD) data obtained in CD3CN demonstrate the expected mirror image spectra for the enantiomers, the observed peaks arising from the dpa ligand. The VCD response is significant, with Δε values up to 6 Lmol−1 cm−1 and vibrational dissymmetry factors on the order of 10−3. Density functional theory calculations well reproduce the experimental spectra, showing little difference between the peak position, sign, and intensity in the VCD for the cobalt and nickel complexes. These results suggest that VCD enhancement of these peaks is unlikely, and their remarkable intensity may be due to their rigid helicoidal structure

    Tris(ethylenediamine) cobalt(II) and manganese(II) nitrates

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    Octahedral tris(ethylenediamine) coordination complexes demonstrate helicoidal chirality, due to the arrangement of the ligands around the metal core. The enantiomers of the nitrate salts [Ni(en)3](NO3)2 and [Zn(en)3](NO3)2 spontaneously resolve to form a mixture of conglomerate crystals, which present a reversible phase transition from space group P6322 to enantiomorphic P6522 or P6122, with the latter depending on the handedness of the enantiomer. We report here the synthesis and characterization of [Mn(en)3](NO3)2 and [Co(en)3](NO3)2, which are isostructural to the Zn(II) and Ni(II) derivatives. The Mn(II) analogue undergoes the same phase transition centered at 150(2) K, as determined by single-crystal X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. The Co(II) derivative does not demonstrate a phase transition down to 2 K, as evidenced by powder X-ray diffraction and heat capacity measurements. The phase transition does not impact the magnetic properties of the Ni(II) and Mn(II) analogues; these high spin compounds display Curie behavior that is consistent with S = 1 and 5/2, respectively, down to 20 K, while the temperature-dependent magnetic moment for the Co(II) compound reveals a significant orbital contribution

    Rapid discrimination of crystal handedness by XNCD mapping

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    An original method for determining the handedness of individual non‐centrosymmetric crystals in a mixture using a tightly‐focused, circularly polarized X‐ray beam is presented. The X‐ray natural circular dichroism (XNCD) spectra recorded at the metal K‐edge on selected crystals of [Δ‐M(en)3](NO3)2 and [Λ‐M(en)3](NO3)2 (M=CoII, NiII) show extrema at the metal pre‐edge (7712 eV for Co, 8335 eV for Ni). A mapping of a collection of some 220 crystals was performed at the respective energies by using left and right circular polarizations. The difference in absorption for the two polarizations, being either negative or positive, directly yielded the handedness of the crystal volume probed by the beam. By using this technique, it was found that the addition of l‐ascorbic acid during the synthesis of [Co(en)3](NO3)2 resulted in an enantiomeric enrichment of the Λ‐isomer of 67±13 %, whereas the Ni analogue was similarly, but conversely, enriched in the Δ‐isomer (65±22 %)

    Enantiopure Chiral Coordination Polymers Based on Polynuclear Paddlewheel Helices and Arsenyl Tartrate

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    Herein, we report the preparation of chiral, one-dimensional coordination polymers based on trinuclear paddlewheel helices [M3(dpa)4]2+ (M = Co(II) and Ni(II); dpa = the anion of 2,2′-dipyridylamine). Enantiomeric resolution of a racemic mixture of [M3(dpa)4]2+ complexes was achieved by chiral recognition of the respective enantiomer by [Δ-As2(tartrate)2]2− or [Λ-As2(tartrate)2]2− in N,N-dimethylformamide (DMF), affording crystalline coordination polymers formed from [(Δ-Co3(dpa)4)(Λ-As2(tartrate)2)]·3DMF (Δ-1), [(Λ-Co3(dpa)4)(Δ-As2(tartrate)2)]·3DMF (Λ-1), [(Δ-Ni3(dpa)4)(Λ-As2(tartrate)2)]·(4 − n)DMF∙nEt2O (Δ-2) or [(Λ-Ni3(dpa)4)(Δ-As2(tartrate)2)]·(4 − n)DMF∙nEt2O (Λ-2) repeating units. UV-visible circular dichroism spectra of the complexes in DMF solutions demonstrate the efficient isolation of optically active species. The helicoidal [M3(dpa)4]2+ units that were obtained display high stability towards racemization as shown by the absence of an evolution of the dichroic signals after several days at room temperature and only a small decrease of the signal after 3 h at 80 °C.Synthèse, caractérisation et mesures Optiques sur composés CHIRaux à Transition de SpinEuropean Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 706556 CHIMMM ( the ANR project CHIROTS ANR-11-JS07-013-01 (Patrick Rosa, PhD fellowship for Ahmad Naim)

    Validation of microscopic magnetochiral dichroism theory

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    International audienceMagnetochiral dichroism (MChD), a fascinating manifestation of the light-matter interaction characteristic for chiral systems under magnetic fields, has become a well-established optical phenomenon reported for many different materials. However, its interpretation remains essentially phenomenological and qualitative, because the existing microscopic theory has not been quantitatively confirmed by confronting calculations based on this theory with experimental data. Here, we report the experimental low-temperature MChD spectra of two archetypal chiral paramagnetic crystals taken as model systems, tris(1,2-diaminoethane)nickel(II) and cobalt(II) nitrate, for light propagating parallel or perpendicular to the c axis of the crystals, and the calculation of the MChD spectra for the Ni(II) derivative by state-of-the-art quantum chemical calculations. By incorporating vibronic coupling, we find good agreement between experiment and theory, which opens the way for MChD to develop into a powerful chiral spectroscopic tool and provide fundamental insights for the chemical design of new magnetochiral materials for technological applications
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