M. M. R. Costa

Conformation of cationic N,N-di­methyl­glycine in di­methyl­glycinium tri­fluoro­acetate

In the title compound, C(4)H(10)NO(2)(+).C(2)F(3)O(2)(-), the main N-C-COOH skeleton of the protonated amino acid is nearly planar. The C=O/C-N and C=O/O-H bonds are syn and the two methyl groups are gauche to the methylene H atoms. The conformation of the cation in the crystal is compared to that given by ab initio calculations (Hartree-Fock, self-consistent field molecular-orbital theory). The trifluoroacetate anion has the typical staggered conformation with usual bond distances and angles. The cation and anion form dimers through a strong O-H.O hydrogen bond which are further interconnected in infinite zigzag chains running parallel to the a axis by N-H.O bonds. Weaker C-H.O interactions involving the methyl groups and the carboxy O atoms of the cation occur between the chains.

Charge densities of two rutile structures: NiF2 and CoF2

X-ray diffraction data were collected at room temperature for two rutile structures, NiF 2 and CoF 2 . Two different crystals of each compound have been used in the experiments. Atomic and thermal parameters were derived from least-squares refinements of high-angle data [(sinθ)λ≥0.6 A -1 ]. The results of Fourier inversion of the differences between observed and model structure factors are presented and discussed in terms of difference density maps

l-Tryptophan 4-nitro-phenol tris-olvate.

The title compound, C(11)H(12)N(2)O(2)·3C(6)H(5)NO(3), comprises a zwitterionic amino acid formed by two nearly planar groups: (i) the indole ring and Cβ, and (ii) the carboxyl group, Cα, as well as the amine N atom, with r.m.s. deviations of 0.0084 and 0.0038 Å, respectively. The angle between these idealized planes is 39.47 (9)°. The amine group of the amino acid is in a syn (-sc) arrangement relative to the ring system. The overall crystal structure results from the packing of sheets parallel to the (001) planes. These sheets are formed by a pair of screw axis related parallel networks bound by hydrogen-bond and π-π stacking interactions. The intermolecular cohesion of all organic residues in each of the latter two-dimensional networks is achieved via strong hydrogen bonding, nitro-π and π-π stacking interactions.

Strong magnetoelastic coupling in orthorhombic Eu1-xYxMnO3 manganite

This work reports an experimental study on the temperature dependence of the structural parameters in orthorhombic Eu1-xYxMnO3 system at low temperatures, by using synchrotron x-ray diffraction technique. A significant magnetoelastic coupling is revealed by anomalies observed in lattice parameters at the magnetic phase transitions, apparent also in both Mn-O bond lengths and Mn-O1-Mn bond angle. Furthermore, signatures of the lattice deformations across the magnetic phase transitions were evidenced by anomalies in the temperature dependence of the lattice mode involving rotations of the MnO6 octahedra. These anomalies confirm the important role of the spin-phonon coupling in these materials.

L-Phenylalanine-4-nitrophenol (1/1).

In the 1:1 adduct formed between L-phenylalanine and 4-nitrophenol [alternative IUPAC name: (2S)-2-ammonio-3-phenylpropanoate-4-nitrophenol (1/1)], C9H11NO2.C6H5NO3, the L-phenylalanine molecule is in the zwitterionic state. The overall structure is stabilized via strong hydrogen bonding between polar zones and van der Waals interactions between non-polar zones, which alternate with the polar zones.

Paramagnetically aligned spin density in the metallic phase of : evidence for orbital exchange correlation

The spatial distribution of the magnetization induced in at 180 K by a field of 4.6 T has been determined using polarized neutron diffraction. At this temperature, which is just above that of the metal-insulator transition, is in the metallic phase which has the rhombohedral corundum structure. The susceptibility, which increases abruptly on raising the temperature through the transition at K, is at 180 K and the moment aligned by 4.6 T at 180 K is 0.0082 /V. The magnetic structure factors were determined from the polarization dependence of the intensities of the Bragg reflections. The results show that the moment on the V atoms is almost entirely due to electrons in the doubly degenerate orbitals which are supposed to give rise to orbital ordering. There is also a significant negative moment amounting to some 6% of the total, associated with the oxygen sites which can only be due to exchange polarization.

Energy-dependent polarization study of the x-ray magnetic scattering in terbium metal

A detailed study of the x-ray magnetic scattering from Tb has been performed, including polarization analysis of the scattered intensity as a function of energy close to the and absorption edges. Large enhancements of the magnetic signal are observed at these energies. It is found that the enhancement at the edge is consistent with a simple dipole transition model, whereas the enhancement at the edge shows an anomalous splitting. The angular and polarization dependences of this resonance are investigated, and various explanations are discussed.

Betainium tri­fluoro­acetate

The title compound, C5H12NO2+*C2F3O2- or BET+*CF3COO- [BET is trimethylglycine (betaine); IUPAC: 1-carboxy-N,N,N-trimethylmethanaminium inner salt], contains pairs of betainium and trifluoroacetate ions forming a dimer bridged by a strong hydrogen bond between the carboxyl and carboxylate groups of the two ions. The molecular symmetry of the cation is close to Cs, with protonation occurring at the carboxy O atom positioned anti to the N atom. The trifluoroacetate anions are disordered over two positions. In one, the conformation of the CF3 group is staggered with respect to the carboxylate group, in the other, it is close to an eclipsed conformation. The sole hydrogen bond present in the structure is the strong O-H...O bond between the anion and the cation.

Sarcosinium tri­fluoro­acetate

The title compound, C(3)H(8)NO(2)(+).C(2)F(3)O(2)(-), crystallizes in space group C2/c. The main N-C-COOH skeleton of the protonated sarcosine molecule is almost perfectly planar. The trifluoroacetate anion has a staggered conformation and typical bond distances and angles. The CF(3) group is probably slightly disordered. The structure is stabilized by an extensive network of strong O-H.O hydrogen bonds and weaker N-H.O bonds.

A magnetic x-ray diffraction investigation of gadolinium selenide

A single-crystal synchrotron radiation study of gadolinium selenide has been made in the temperature range 15 - 100 K. GdSe has the rocksalt structure and becomes antiferromagnetic below a reported Neel temperature of 65 K. At 15 K, magnetic reflections are observed at with modulation wavevector propagating from reciprocal lattice point G. This is achieved by exploiting the resonant enhancement in the vicinity of the and edges. Similar enhancements are observed at the two edges, with the maximum effect occurring approximately 3 eV above the absorption edge. The temperature dependence of the intensity of the magnetic reflections indicates a Neel temperature of 63(1) K. These measurements, together with high-resolution studies of the fundamental reflections , contribute further evidence of magnetic or structural changes in the sample at 37(1) K. Our observations are discussed and compared with previous x-ray diffraction and magnetic susceptibility measurements.