First- and Second-Order Thermal Diffuse Scattering (TDS) Intensity in Molecular Crystals: Influence on Crystal Structure Parameters

First- and second-order thermal diffuse scattering (TDS) intensities are calculated in the long-wave approximation allowing for dispersion (LWD) in monoclinic phenothiazine from polarization vectors and lattice-mode frequencies obtained from lattice dynamical calculations within the harmonic approximation and the external Born-von K~irmfin formalism using an atom-atom potential function in the form V(r) =-A/r6+ B exp (-Cr). The influence of firstand second-order TDS intensity on electronic density maps is analysed and compared. Least-squares refinements of positional and thermal parameters are carried out in different ranges of sin 0/A taking into account both first- and second-order TDS contributions and the results are discussed

Structure of 4-(~-D-Erythrofuranosyl)-3-methyl- l-(p-tolyl)-4-imidazoline-2-thione Monohydrate, C 15H18N203S.H20

Mr=324.4, orthorhombic, P212t2 ~, a= 32.150(5), b=10.215(1), c=4.805(1)A, V= 1578.0 (4)/~3, Z = 4, D x = 1.36 Mg m -a, 2(Cu Ka) = 1.5418A, #=1.953mm -1, T=300K, final R= 0.050 for 1361 observed [I>2tr(I)] independent reflexions. The sugar ring adopts a conformation intermediate between envelope 2E and twist 2T forms. The orientation of the imidazoline ring with respect to the furanose is anti; the glycosidic angle is 24.6 (7) °. The crystal packing is due to hydrogen bonds involving the hydration water molecules

Lattice-Dynamical Calculation of Second-Order Thermal Diffuse Scattering in Molecular Crystals

A computer procedure has been developed to calculate second-order thermal diffuse scattering (TDS) intensity for molecular crystals from latticedynamical calculations with an atom-atom potential in the Born-von K~irmfin formalism. It is applied to monoclinic phenothiazine and different contributions to second-order TDS intensity, acoustic-acoustic, acoustic-optic and optic-optic, are compared. Calculations are also performed in the long-wave approximation allowing for dispersion (LWD) and correction factors of Bragg intensities due to TDS contribution in the LWD approximation are, generally but not always, lower than lattice-dynamical ones; the ratio between LWD and 'exact' factors ranges from 0.4 to 1.4 for reflections considered

Structure of 1,3-Dihydro-4-[(2R)-2,5-dihydro-2-furyl]-3-phenyl-l-(p-tolyl)-2H-imidazole- 2-thione, C20HlsN2OS

Mr=334.4, orthorhombic, P212~2 ~, a= 9.366(4), b=20.616(5), c=9.137(4)A, V= 1764 (1) A 3, Z = 4, D x = 1.26 Mg m -3, 2(Mo Ka) = 0.7107 A, g = 0.18 mm -~, F(000) = 704, T= 300 K, final R--0.056 (wR =0.052) for 1979 observed reflections [I > 2a(/)]. The furanose ring is approximately planar because of the double bond, 1.289 (9) A, which affects the conformation of the ring. The dihedral angle between the furanose and imidazole least-squares planes is 69.9 (2) °. A possible C--H...O hydrogen bond has been detected involving C and O atoms in the furanose ring, giving infinite helical chains along [001 ]

Lattice Dynamical Calculation of First-Order Thermal Diffuse Scattering in Phenothiazine

A computer program has been developed to calculate first-order thermal diffuse scattering (TDS) intensity from eigenvectors and eigenvalues of the dynamical matrix obtained within the harmonic approximation with an atom-atom potential function and the external Born-yon Kfirmfin formalism. It is applied to monoclinic phenothiazine and correction factors of Bragg intensities due to TDS contribution are calculated and compared with the long-wave approximation. A Fourier difference synthesis is performed in order to reveal the influence of TDS contributions in electron density maps. A least-squares process is carried out to obtain the changes in structural parameters due to TDS contribution

Lattice Dynamics and Thermal Crystallographic Parameters in Phenothiazine

A computer program has been developed to study the lattice dynamics of molecular crystals in the harmonic approximation with the external Born-yon KS.rm~n formalism and an atom-atom potential function. Dispersion curves are obtained for monoclinic phenothiazine together with frequency distribution functions and external mode contribution to thermodynamic functions. Lattice dynamical T, L and S rigid-body tensors are obtained and individual thermal tensors are compared with experiment. The disagreement with respect to experimental results is of the same order as the disagreement with a Schomaker-Trueblood fit of experimental data

Structure of l-(p-Ethoxyphenyl)-1,3-dihydro-3-phenyl-2H-benzimidazole-2-thione, C2IHlaN2OS

Mr=346-4, orthorhombic, P212121, a= 7.600(1), b= 11.132(2), c=20.767 (3)A, v= 1756.9(5)A 3, z=4, Dx=1.31Mgm -3, 2(CuKct) =.1.5418/k, /~= 1.67mm -1, F(000)=728, T= 300 K. Final R = 0.049 for 1531 observed independent reflections. The benzimid~zole bicycle is quasi-planar, the dihedral angle between the two fused rings being 1.6 (2) °. The unsubstituted phenyl ring is planar while the phenyl ring with the ethoxy substituent deviates significantly from the expected planar conformation

Structure and Absolute Configuration of 4-(a-D-Erythrofuranosyl)-1,3-dihydro-3-methyll-( p-tolyl)-2H-imidazole-2-thione, C 15 H18N2038

M r = 306.4, monoclinic, P21, a = 14.686 (6), b=5.359(4), c=9.439(3) A, fl=98.68(3) ° , V= 734.4 (7)/I,3, Z = 2, D x = 1.38 Mg m -3, 2(Mo Kct) = 0.7107 A, /t = 0-22 mm -1, F(000) = 324, T= 300 K, final R=0.042 (wR=0.037) for 1987 observed independent reflections. The sugar ring has a conformation intermediate between 3T 2 and 3E. The configuration of the imidazole ring with respect to the furanose ring is anti, the glycosidic angle being -9.3 (4) ° . The crystal packing is governed by hydrogen bonds involving OH groups and S atoms, forming infinite chains along [001]

Tienen importantes efectos por separado, pero cuando se juntan, los pierden

Premio extraordinario de Trabajo Fin de Máster curso 2016-2017. Máster en Profesorado de Enseñanza Secundaria Obligatoria, Bachillerato, Formación Profesional y Enseñanza de Idioma

Síntesis y caracterización de derivados composicionales del Na3V2(PO4)3 como electrodos positivos en baterías de ion sodio

Premio extraordinario de Trabajo Fin de Máster curso 2018/2019. Máster en QuímicaSe han sintetizado compuestos C@Na3V2-xAlx(PO4)3 altamente sustituidos con Al y que presentan una estructura tipo NASICON mediante una ruta sol-gel sencilla, fácilmente escalable y muy reproducible. Se prepararon varias muestras modificando el valor de pH de la disolución precursora, la temperatura de calcinación y el contenido de Al para optimizar el comportamiento electroquímico de este material como cátodo en baterías de ion sodio. Se han estudiado sus características estructurales, químicas y morfológicas utilizando técnicas de estado sólido, como la difracción de rayos X, espectroscopías Raman y XPS, 27Al MAS NMR y microscopías electrónicas. La extracción electroquímica de Na se caracteriza por la presencia de dos mesetas bien diferenciadas. La primera meseta, que aparece aproximadamente a 3.4 V, muestra una elevada ciclabilidad y se debe al par redox V4+/V3+. La segunda meseta, a aproximadamente 4.0 V, corresponde al par redox V5+/V4+, como demuestra la técnica de XPS. Esta segunda meseta es menos reversible durante la siguiente descarga. La muestra Na3V1.2Al0.8(PO4)3 proporciona una capacidad de 89 mA·h·g-1 y una excelente eficiencia culómbica incluso en la meseta de alto voltaje.Highly Al substituted C@Na3V2-xAlx(PO4)3 compounds, with a NASICON structure, are synthesized by a single and easily scalable sol-gel route. Several samples were prepared by changing the pH value of the precursor solution, calcination temperature and Al content to optimize the electrochemical behavior as cathode for sodium-ion batteries. Their structural, chemical and morphological features will be described at the light of solid state powerful techniques such as X-Ray diffraction, Raman, and XPS spectroscopies, 27Al MAS NMR and electron microscopies. The electrochemical Na extraction is characterized by the presence of two plateaus. The first one at ca. 3.4 V is assigned to the V4+/V3+ redox pair, and show a good cyclability. The second plateau at ca. 4.0 V can be assigned to the V5+/V4+ pair, as evidenced by XPS. This second plateau is less reversible during further discharge. Na3V1.2Al0.8(PO4)3 delivers 89 mA h g-1 and excellent coulombic efficiency even at the high voltage plateau