N. A. Didenko

NMR, DTA, and Impedance Spectroscopy Studies of Ion Mobility, Phase Transitions, and Ionic Conductivity in K 1- x (NH 4 ) x SbF 4 Crystals

The ion mobility, phase transitions, and ionic conductivity in the crystal phases in the KF-NH4F-SbF3 system were studied by NMR, DTA, and impedance spectroscopy. An analysis of the 19F and 1H NMR spectra showed how the character of ionic motions in the fluoride and proton sublattices changed with temperature. The types and temperature ranges of ionic motions were determined. Diffusion of the fluoride and partially ammonium ions was found to be the dominant form of ionic motion in the high-temperature modifications formed as a result of phase transitions. According to the electrophysical data, the high-temperature K1 − x(NH4)xSbF4 phases (0.05 ≤ x ≤ 0.75) are superionic, their conductivity reaching ∼10−2–10−3 S/cm at 450–500 K.

Synthesis and studies of magnesium hexafluorozirconates MgZrF6 · nH2O (n = 5, 2, 0)

Crystalline magnesium hexafluorozirconate MgZrF6 · 5H2O isostructural to MnZrF6 · 5H2O, and having a chain-like structure, was synthesized and studied. According to thermogravimetry, the compound undergoes stepwise dehydration in the temperature range of 50–420°C to give the stable phase MgZrF6 · 2H2O and the final product MgZrF6 isostructural to the cubic modification of MZrF6 (M = Cu, Fe). The vibrational spectra of the initial compound and the dehydration products are analyzed and the structures of the compounds are considered.

Synthesis and complex investigation of potassium ammonium hexafluorozirconates: I. Synthesis and X-ray diffraction study of K2-x(NH4)xZrF6 (0 < x < 2) crystals

The synthesis and X-ray diffraction study of compounds K2-x(NH4)xZrF6 (0 < x < 2) were carried out. In all crystals of mixed composition, potassium cations are isomorphously replaced by ammonium cations. The compounds with x < 0.5 are isostructural to K2ZrF6 and those with x > 1.5, to (NH4)2ZrF6. At 0.5 < x < 1.5, the structures are built of linear polymeric chains formed by edge-sharing Zr dodecahedra. The distribution of potassium and ammonium cations over the cationic positions was considered.

Li2Mg(ZrF6)2 · 4H2O: Synthesis, X-ray crystallographic, thermal, and MAS NMR study

A new zirconate with lithium and magnesium cations of composition Li2Mg(ZrF6)2 · 4H2O (I) has been synthesized and studied by different methods (X-ray crystallography, differential thermal analysis, IR spectroscopy, and NMR (1H, 7Li, 19F, including 19F MAS NMR). The framework structure of I is composed of edge- and vertex-sharing ZrF8 dodecahedra, Mg(Ow)2F4 octahedra, and Li(Ow)F4 square pyramids. The structure is additionally stabilized by O-H...F and O-H...O hydrogen bonds. Compound is dehydrated in one stage in the temperature range 105–200°C to form Li2Mg(ZrF6)2 (II). The latter undergoes irreversible phase transition at 365°C leading to its decomposition into a mixture of MgZrF6 (cubic) and Li2ZrF6 (hexagonal). According to IR and NMR data, the structure of fluorozirconate chains of compound I is retained after dehydration.

Thermal properties and ion mobility in complex antimony(III) fluorides with α-amino acids

Differential thermal analysis (DTA) and (19F, 1H) NMR spectroscopy were used to study thermal properties and ion mobility in complex antimony(III) fluorides with amino acids of composition [(CH3)2CH(CH2)CH(NH3)COOH]SbF4 (LeuHSbF4), SbF3[(CH3)2CH(CH2)CH(+NH3)COO−] (SbF3 · Leu), and SbF3[(CH3)2CHCH(+NH3)COO−] (SbF3 · Val). Ionic conductivity in L-leucinium tetrafluoroantimonate(III) was studied using impedance spectroscopy. LeuHSbF4 was found to undergo a diffusion phase transition to a relatively highly conductive state in the range 385–415 K with an attendant loss of thermal stability (softening) of the high-temperature phase.

Synthesis, Structure, Ion Mobility, Phase Transitions, and Ion Transport in Rubidium Ammonium Hexafluorozirconates

Rubidium ammonium hexafluorozirconates Rb2−x (NH4)x ZrF6 (1.5 < x < 2.0) have been synthesized, and their structure, ion mobility (180–480 K), and electrophysical properties have been studied by X-ray crystallography, 1H and 19F NMR, DTA, and impedance methods. Compounds with x > 1.5 are isostructural with (NH4)2ZrF6. Rubidium cations are isomorphously substituted for the ammonium cations. The high-temperature modifications of the compounds, which form upon the phase transitions at 413–418 K, are characterized by translational diffusion of ions in the fluoride and ammonium sublattices. The 19F NMR spectra are characterized by uniaxial 19F magnetic shift anisotropy. The electrophysical properties of this series of compounds are studied in the temperature range 300–480 K.

Synthesis and complex study of potassium ammonium hexafluorozirconates: Ion mobility, phase transitions, and ionic conductivity in K2−n(NH4)nZrF6 compounds as probed by NMR, DTA, and impedance spectroscopy

The mobility of the fluoride and ammonium ions (180–480 K) in K2−n(NH4)nZrF6 compounds (0.2 ≤ n ≤ 1.80) has been studied by 19F and 1H NMR. Correlations between the composition of the cationic sublattice, the character of ion motions, and the phase-transition temperature in these compounds have been established. The high-temperature modifications of compounds with n ≥ 1 are characterized by translational diffusion of ions in the fluoride and ammonium sublattices, and their 19F NMR spectra are characterized by uniaxial chemical shift anisotropy. The electrophysical properties of these compounds are studied in the range 300–480 K.

Structure of ZnZrF6 · nH2O (n = 6–2) and ZnZrF6 crystallohydrates according to vibrational spectroscopy data

Fluoridezirconate crystallohydrates ZnZrF6 · nH2O (n = 6–2) and anhydrous ZnZrF6 are investigated by vibrational spectroscopy and thermography. The influence of the hydrate number on the structure of the cationic and anionic sublattices of the crystallohydrates is studied. The changes in the strength of HOH···F and HOH···O hydrogen bonds of coordinated and outer-sphere water molecules occurring with variations in the hydrate number are determined by changes in the IR spectra. The IR spectra of ZnZrF6 · nH2O (n =6, 4) compounds, which have isolated complex anions [ZrF6]2– in their structure, revealed a band with two peaks in the range of 3470–3430 cm–1, which corresponds to stretching vibrations of coordinated water molecules. The spectra of ZnZrF6 · nH2O (n = 5, 3, 2, 1) crystallohydrates with a polymeric structure show a high-frequency shift of this band, which corresponds to weakening of hydrogen bonds. The vibrations of crystallization water molecules involved in the network of strong O–H···F and O–H···O hydrogen bonds manifest themselves in the spectra of ZnZrF6 · nH2O (n =5, 3) crystallohydrates by broad structureless bands in the region of stretching, bending, and libration vibrations.

An NMR study of the structure of hydrated fluorophosphatozirconates (hafnates)

Abstract31P, 19F, 1H NMR is used to study fluorophosphatometalates of the composition MHfF2PO4·0.5H2O (M = Rb, Cs) and CsMe2F6PO4·4H2O (Me = Zr, Hf). The data obtained indicate the isostructurality of compounds in each of these two groups. The lines in the NMR spectra are assigned. Assumptions about the character of the bond of PO4 groups and F atoms with Me are made and schemes of the crystal structure of fluorophosphatometalates are proposed. The occurrence of several types of crystallization water characterized by different bond strengths and energy barriers of the diffusion motion is found.

Ionic mobility in heptafluorozirconantes with a mixed cationic sublattice as probed by 1H and 19F NMR

The ionic mobility in heptafluorozirconates (NH4)2.7Rb0.3ZrF7 and (NH4)2.75Cs0.25ZrF7 has been studied by 1H and 19F NMR in the temperature range 150–430 K. The types of ion motion were determined and their activation energies were estimated. A phase transition results in a modification in which diffusion in the ammonium sublattice and orientational disorder of ZrF73− anions are observed. Owing to diffusion of ammonium ions, the compounds have relatively high ionic conductivity (σ ≥ 5 × 10−5 S/cm at 420 K).