Bis[glycinium(0.5+)] perrhenate

All the residues of the title compound, (C2H5.5NO2)2[ReO4], are located in general crystallographic positions. The glycine mol­ecules have usual conformations [Rodrigues Matos Beja et al. (2006 ▶). Acta Cryst. C62, o71–o72] with the H atom of the carboxylate group half-occupied, thus bearing a formal half-positive charge per molecule. The perrhenate anion has nearly ideal tetra­hedral geometry. A large number of strong hydrogen bonds give rise to the overall three-dimensional network. A two-dimensional network, parallel to (100), is made up of strong O—H⋯O hydrogen bonds with a donor acceptor distance of 2.445 (2) Å. A large number of weaker O—H⋯O and N—H⋯O hydrogen bonds consolidates the structure into an overall three-dimensional network

2-Amino-5-nitro­pyridinium tetraoxido­rhenate(VII) monohydrate

All the residues of the title compound, (C5H6N3O2)[ReO4]·H2O, are located on general crystallographic positions. The 2-amino-5-nitro­pyridinium cation has a typical planar conformation with one of the nitro O atoms −0.058 (5) Å out of plane; the amine H atoms are also a little out of the main ring plane towards the opposite side of the aforementioned O atom [by 0.02 (4) and 0.04 (4) Å]. The perrhenate anion is nearly ideally tetra­hedral. Three distinct N—H⋯O hydrogen bonds give rise to C(8) zigzag chains running along [100]. R 4 4(12) rings involving the two hydrogen bonds in which the water mol­ecules inter­act with the perrhenate anions are also present

Orientation-switching transition and ferroelectricity in betaine arsenate

This paper reports a detailed investigation of the low frequency dielectric relaxation of betaine arsenate near the ferroelectric phase transition. The dielectric relaxation data are complemented with polarized infrared reflectivity data taken at low temperatures. The reported results allow us to identify several low frequency modes that clarify the complex behaviour of the dielectric response near the Curie temperature Tc2 ≈ 120 K. It is suggested that the important slow dynamics observed is linked to the reorientation of the betaine molecular group. The roles of the different molecular units in the structural changes are briefly discussed and a new and more complex phase transition sequence is propose

Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH3)(3)NCH2COO center dot H3AsO4]

The present work reports an experimental investigation on the influence of glycine(NH2CH2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate,(CH3)(3)NCH2COO center dot H3AsO4. The dielectric dispersion (20 Hz < v < 3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K < T < 100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities. (C) 2011 Elsevier B.V. All rights reserved.The authors wish to thank to Prof. M. R. Chaves. This work was supported by Fundacao para a Ciencia e Tecnologia through the Grant SFRH/BPD/26931/2006

The phase transition sequence of betaine arsenate investigated by infrared reflectivity

The ac-polarized infrared reflectivity spectra of betaine ortho-arsenic acid single crystals have been measured throughout the ferroelastic–ferroelectric phase transition observed near Tc2 = 120 K. The monoclinic symmetry of the system was explicitly taken into account and a three-polarization technique used for the first time to investigate in detail the critical behaviour of the Bu polar phonons. The results show that near the THz frequency range, the usual approximation of considering the system as pseudoorthorhombic fails, giving rise to errors in the determination of the optical parameters. The obtained spectroscopic data indicate that the phase diagram and the physical mechanism involved in the stabilization of ferroelectricity in betaine arsenate (BA) are more complex than the prevalent view of a simple ordering process in bistable hydrogen bonds

Polarized hydrogen bonds and dielectric properties of glycine glicinium perrhenate

Glycine glycinium perrhenate is a new hydrogen bonded crystalline material that exhibits several phase transitions at low and high temperature. At room temperature the structure shows some special features. One dimensional polar chains, linked by strong hydrogen bonds exist parallel to [100], [010] and [–110]. The structural, thermal and dielectric properties of this new perrhenic salt are presented and a relationship is established