V.Y. Kavun et al.
JournalofFluorineChemistry217(2019)50–57
Fig. 8. The structure of the complex anion [Sb2F7]‾.
3. Conclusions
the temperature range 460–490 K (maximum at 473 K) is related to
decomposition of the (C5H12NO2)SbF4·H2O (I) compound with forma-
tion of metal antimony (XRD data). In case of the (C3H8NO3)Sb2F7 (II)
compound in the temperature range 300–450 K, the DSC curve contains
one irreversible endothermal effect with a maximum at 385 K, which is
associated with the formation of X-ray amorphous phase.
a) The crystal structure of the (C5H12NO2)SbF4·H2O compound has
been determined. The structure is composed of DL-valunium cations
n–
(C5H12NO2)+, complex [SbF4]n anions, and crystallization water
n–
molecules. Complex [SbF4]n anions consist of trigonal SbF4E bipyr-
amids linked to each other through asymmetric bridge Sb–F(3)···Sb’
bonds. The coordination polyhedra of Sb atoms within the first co-
ordination sphere comprise ψ-trigonal SbF4E bipyramids. Through
asymmetric bridge Sb–F···Sb’ bonds (2.042 and 2.584 Å, respectively),
4.2. DSC study
The thermal properties of (C5H12NO2)SbF4·H2O and (C3H8NO3)
Sb2F7 compounds were carried out using a DSC-204-F1 differential
scanning calorimeter (NETZSCH) in the temperature range 300–500 K
in heating and cooling modes at a rate of 10 deg/min in dry argon
atmosphere. In order to obtain more reliable experimental data, the
heating-cooling cycles of the samples were repeated several times. The
error in measuring the temperature of thermal effects on the DSC curve
did not exceed 1 K.
n–
polyhedra are linked to each other forming bent anionic [SbF4]n
chains stretched along the crystal b axis. Through N–H…F, N–H…O and
O–H…F hydrogen bonds, the structural units are linked into a three-
dimensional framework.
b) It has been established that the absence of ionic mobility with
frequencies above 104 Hz in I in the studied temperature range could be
related to the presence of strong hydrogen bonds in the structure of I.
The emergence of mobile protons in II is observed above 210 K.
Complete disorder character of the proton sublattice occurs in the
temperature range 330–350 K, when the proton diffusion becomes a
predominant type of ionic mobility. Intensive dynamic processes in the
proton subsystem of II in the temperature range 320–350 K precedes
the phase transition of the order–disorder type (irreversible endo-effect
at 385 K), which makes the compound X-ray-amorphous. The emer-
gence of mobile fluoride ions in II above 260 K is, probably, related to
the starting exchange between end fluorine atoms in trigonal SbF4E
bipyramids, so that at 320 K the number of ions participating in diffu-
sion constitute 22 % of total number of anions in the compound lattice.
4.3. NMR study
The 19F and 1H NMR static spectra of the polycrystalline
(C5H12NO2)SbF4·H2O and (C3H8NO3)Sb2F7 compounds were recorded
using a Bruker AVANCE-300 spectrometer at Larmor frequencies
νL = 282.404 MHz (for 19F nuclei) and νL = 300.13 MHz (for 1H nuclei)
and temperatures from 150 to 420 K (
2 K). One pulse sequence with
2 μs pulse width was used, the relaxation delay was 5 s, and the sam-
pling frequency corresponding to the spectral width was from 1 to
5 MHz. Calculations of the RMS width of NMR spectra (or the second
moment S2, in G2) were performed using an original code by formulas
given in [34]. The full width at half maximum of an integral line (ΔH ,
4. Experimental
½
kHz) and the chemical shift (CS) (ppm vs. CFCl3) were estimated from
the spectra with an accuracy of 2 % and 1 ppm, respectively. The
chemical shift in 1H NMR static spectra was measured relatively to
tetramethylsilane (TMS). Simulations of experimental 19F (H) NMR
spectra with an error below 10 % were carried out by the original
computer program, which allows performing the spectrum deconvolu-
tion into components and determining their parameters. Squares of the
NMR components were measured with an error below 5 %. The tech-
nique for measuring the parameters of the NMR spectra is described in
[6]. The activation energy (ENMR) of local motions was estimated by the
Waugh–Fedin equation ENMR = 0.0016∙Tc (eV) with an accuracy of
0.03 eV [31]. Tc was taken as the onset temperature (absolute scale) for
4.1. Synthesis
The synthesis of the compounds (C5H12NO2)SbF4·H2O (I) and
(C3H8NO3)Sb2F7 (II) was carried out by the preparative method
through interaction of SbF3 (chemically pure grade) with DL–valine
(C5H11NO2, pure grade) and DL–serine (C3H7NO3, pure grade) taken at
1:1 and 0.5:1 molar ratios, respectively, in aqueous solutions in the
presence of HF. Samples of initial substances were dissolved in water at
heating up to ∼50–60 °C, then the solutions were mixed. Hydrofluoric
acid was added to attain the solution acidity of pH 1–2. The obtained
solution was evaporated to 1/3 of the initial volume and left for slow
crystallization at room temperature. The formed crystalline substance
was filtered under vacuum and dried in air until constant weight.
Individuality of the obtained compound was corroborated by standard
methods of chemical, X-ray diffraction, and IR spectroscopy analyses.
To synthesize the compound I, 3.27 g of C5H11NO2 and 5 g of SbF3 were
used; the substance yield was 5.15 g (92 %). To synthesize the com-
pound II, 2.94 g of C3H7NO3 and 10 g of SbF3 were used; the substance
yield was 12.50 g (93 %). Chemical analysis: the Sb content was (%):
37.03 (found) and 36.47 (calculated) for the compound I and 50.65
(found) and 50.46 (calculated) for the compound II. The endo-effect in
a decrease of the second moment S2 (or linewidth ΔH ) of 19F NMR
½
spectra.
4.4. X-ray study
Powder X-ray diffraction data (XRD) were recorded at 300 K using a
Bruker D8 ADVANCE diffractometer on CuKα radiation.
The X-ray structure measurements were performed using a single
crystal of a lamellar shape using a Bruker KAPPA APEX II diffractometer
(MoKα-radiation, graphite monochromator). The experimental data were
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