Properties of fluoroantimonates(III) complexes with amino acids

Article abstract of DOI:10.1134/S1070363214050223

Crystalline complex fluoroantimonates(III) with amino acids (glycine, β-alanine, DL-serine, DL-valine, L-leucine, and L-phenylalanine) have been prepared. The complexes stability in aqueous solutions has been studied with the cementation method. ¹

Full text of DOI:10.1134/S1070363214050223

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 5, pp. 918–922. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © L.A. Zemnukhova, T.A. Babushkina, T.P. Klimova, N.V. Makarenko, E.V. Kovaleva, 2014, published in Zhurnal Obshchei Khimii,
2014, Vol. 84, No. 5, pp. 825–830.
Properties of Fluoroantimonates(III) Complexes
with Amino Acids
L. A. Zemnukhovaa, T. A. Babushkinab, T. P. Klimovab,
N. V. Makarenkoa, and E. V. Kovalevaa
a Institute of Chemistry, Far-Eastern Branch, Russian Academy of Sciences,
pr. 100-letiya Vladivostoka 159, Vladivostok, 690022 Russia
e-mail: makarenko@ich.dvo.ru
b Nesmeyanov Institute of Elementoorganic Compounds, Russian Academy of Sciences, Moscow, Russia
Received August 19, 2013
Abstract—Crystalline complex fluoroantimonates(III) with amino acids (glycine, β-alanine, DL-serine, DL-
valine, L-leucine, and L-phenylalanine) have been prepared. The complexes stability in aqueous solutions has
been studied with the cementation method. 1H NMR studies of aqueous solutions of the amino acids complexes
with SbF3 at рН 1–6 and room temperature are reported. Preparation of polycrystalline metal antimony in
aqueous solutions of tetrafluoroantimonates(III) complexes with the protonated amino acids has been
demonstrated.
Keywords: antimony(III) fluoride, amino acid, fluoroantimonate(III), 1H NMR
DOI: 10.1134/S1070363214050223
Antimony trifluoride is known as excellent acceptor
of fluoride ions and therefore forms a wide family of
complex compounds, their composition, structure, and
properties being dependent on the nature of interacting
species. Fluoride complexes of antimony(III) with
cations of alkali metals and ammonium are the most
well studied; among these compounds, substances with
important utilitarian properties have been found, for
instance, piezoelectrics and ion conductors [1, 2],
biologically active compounds inhibiting growth of the
tumor (Ehrlich’s carcinoma) cells and affecting
activity of the marine bacteria [3, 4]. Antimony
trifluoride, as a representative of р-element compound
in the non-complete valence state can form complexes
with organic ligands. Such complexes, in particular,
those with amino acids, are scarcely studied compared
to complexes of amino acids with transition metals [5,
6]. To date, the SbF3 complexes with glycine (Gly) [7,
8], β-alanine (Ala) [9], DL-serine (Ser) [10], DL-
valine (Val) [11], L-leucine (Leu) [12, 13], and L-
phenylalanine (Phe) [14] have been described in the
literature. Thermal properties of the complexes with
Leu and Val as well as their ionic mobility as function
of temperature at 150–420 K have been studied [15].
Extending our previous studies of complexes of
antimony(III) fluoride with amino acids, herein we
report on properties of their aqueous solutions as studied
by cementation method and 1H NMR spectroscopy.
Composition of the prepared complex fluoro-
antimonates(III) and some of their structural features
are collected in Table 1. According to the composition,
the compounds could be divided into two groups:
molecular adducts nSbF3·X (X = Gly, Val, Leu, and
Phe; n = 1, 2) and tetrafluoroantimonates(III) of
univalent cations of protonated amino acids (Gly, β-
Ala, Ser, Val, and Leu). Coordination polyhedrons of
antimony(III) were either tetragonal (SbF4E, SbF3OE)
or octahedral (SbF5E, SbF3O2E) bipyramid with one of
the vertexes being occupied with lone pair (Е) of Sb3+.
Antimony atoms generally occupied the equivalent
positions in the crystal unit cell, the [LeuH]SbF4
complex with two different positions of the central
atom being an exception. In the molecular adducts and
in the complex tetrafluoroantimonates(III), antimony
polyhedrons were combined with the amino acid or its
protonated cation into three-dimensional scaffold or
polymeric chains, the [GlyH]SbF4, complex containing
isolated SbF4Е groups being an exception.
918

PROPERTIES OF FLUOROANTIMONATES(III) COMPLEXES
919
Table 1. Complex fluorides of antimony(III) with amino acids and their structural features
Amino acid
Glycine
Complex composition
Antimony polyhedron
Arrangement type
2SbF3·Gly [8]
SbF3·Gly [8]
SbF4E
Three-dimensional scaffold
SbFO·Gly [8]
[GlyH]SbF4 [8]
[β-AlaН]SbF4·H2O [9]
[β-AlaH]SbF4 [9]
[SerН]SbF4 [10]
SbF3·Val [11]
SbF4E
SbF4E
SbF4E
SbF4E
SbF3O2E
Isolated groups SbF4
β-Alanine
Polymeric chains [SbF4]nn–
Polymeric chains [SbF4]nn–
Polymeric chains [SbF4]nn–
Polymeric chains
DL-Serine
DL-Valine
[ValН]SbF4·H2O [11]
SbF3·Leu [12]
L-Leucine
SbF3OE
SbF4E,а SbF5Eb
Three-dimensional scaffold
Polymeric chains [Sb2F8]n2n–
[LeuН]SbF4 [13]
SbF3·Phe [14]
L-Phenylalanine
a Fig. 1. b Fig. 2.
SbF3O2E
Polymeric chains of SbF3 and Phe
groups
Stability of antimony(III) fluoride complexes was
studied by cementation method; results are sum-
marized in Table 2. Yield of antimony was affected the
starting compound composition and ranged in between
47.6% and 96.2%. Recovery of antimony from the
solutions containing fluoride complexes of antimony
(III) with the F : Sb ratio of 3 was of 50–62.5%. 74.5%
of the pure metal could be isolated from the solution of
KSb2F7 (F : Sb of 3.5), whereas solutions of complex
pentafluoroantimonates(III) (F : Sb of 5) yielded 47.6–
85.7% of metal antimony. The highest yield of anti-
mony (about 96%) could be obtained from the solu-
tions of tetrafluoroantimonates(III) with protonated
amino acids.
Sb8O11Cl2·6H2O (47%). Compound of the latter com-
position was prepared earlier under different condi-
tions [17]. Hence, in order to obtain the highest yield
of antimony, application of aqueous solutions of anti-
mony(III) complex fluorides is advantageous, the best
results being achieved in the case of tetrafluoro-
antimonates(III) with the amino acids cations.
Rate of the metal precipitation depends on its
concentration in the solution [18]. Evidently, amount
Table 2. Yield of metal antimony from aqueous solutions of
complex fluorides of antimony(III) as function of their
compositiona
Morphology of the metal antimony specimens is
shown in Fig. 1. The antimony particles were built of
complex needle-shaped crystals (dendrites), 2 to 20 μm
long and about 1.2 μm thick. Composition of metal
antimony samples isolated from solutions of the
complex fluorides was close to that recommended for
production of lead antimonate, anti-frictional alloys
and alloys for cable shell and universal batteries [16].
Compound Sb yield, %
Compound
Sb yield, %
SbF3
62.5
51.4
50.0
74.5
92.8
73.0
70.5
NH4SbF4
91.8
94.6
96.2
81.5
85.7
47.6
SbF3Leu
SbF3Phe
KSb2F7
NaSbF4
KSbF4
AlaНSbF4
ValНSbF4H2O
LeuНSbF4
K2SbF5
In order to find the best source of metal antimony,
solution of antimony trichloride in aqueous hydro-
chloric acid were studied. In that case, cementation
yielded the precipitate containing metal antimony
(52.8%) and antimony(III) oxochloride crystal hydrate
(NH4)2SbF5
CsSbF4
a
Fluoride complexes of antimony(III) were prepared as described
elsewhere [1, 3].
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ZEMNUKHOVA et al.
(a)
(b)
2 μm
2 μm
Fig. 1. Microscopy of metal antimony. (a) Magnification ×500; (b) magnification ×1000.
of metal antimony formed in course of cementation
depends on the ions concentration [or, in other words,
on stability of Sb(III) fluoride complexes in aqueous
solutions] as well. Noteworthily, attempts to elucidate
the complexes structure in solution have been
described [19], but their hydrolysis has not been yet
studied in detail.
of 2SbF3·Gly complex (Fig. 2a). However, at рН > 5
chemical shifts of the 1 : 1 complex signals coincided
with those of the pure amino acid.
In the case of complex with valine SbF3·Val, at рН
1.5–2.5 signal of the α-proton moved downfield as
compared to pure valine, pointing at the complex
formation. Under such conditions, СООН group of the
amino acid dissociated. Cleavage of the O–Sb bonding
occurred at higher pH (Fig. 2b).
Stability of fluoroantimonates(III) with amino acids
1
in aqueous solutions has been studied by H NMR
spectroscopy. The most prominent change of chemical
shifts as function of pH was observed in the case of
proton of the NH2CHα(β) group, the closest to the
protonation site; that was in agreement with the
Chemical shifts of the β-protons in the complex
with β-alanine β-AlaHSbF4 were practically the same
as those in the case of pure β-alanine (Fig. 2b), point-
ing at fairly weak bond between Sb atom and the ligand.
1
published data [20]. Changes of H NMR chemical
Complex with leucine LeuHSbF4 was more stable
than the complexes of other amino acids, and existed
over wider pH range. Even at рН 7, the α-proton
chemical shift deviated from that of the pure amino
acid (Fig. 2c).
shifts of the amino acids (Glu, β-Ala, Val, Leu, and
Phe) and their complexes with antimony(III) fluorides
correlated with dissociation constant of the amino aids
СООН group (рK1 2 and 3 [20]) (Fig. 2).
Chemical shifts of the α-protons1 in the amino acids
complexes with SbF3 were close to those of the
corresponding amino acids, pointing at fairly low
stability constant in aqueous solutions. In neutral
solutions, in the cases of all the studied complexes
except for that with leucine, LeuHSbF4, (Fig. 2c),
chemical shift of the α-proton equaled that of the pure
amino acid.
Complex with phenylalanine SbF3·Phe revealed
upfield shift of the α-proton signal as compared with
that of the pure amino acid; the complex was stable at
рН ≤ 4 (Fig. 2c).
The low yield (about 50%) of metal antimony upon
cementation of the complexes with leucine and
phenylalanine (Table 2) coincided with the higher
stability of those complexes as compared with com-
In the case of complex with glycine SbF3·Gly,
position of the α-proton signal at рН of 2–5 deviated
more from that of the pure amino acid than in the case
1
plexes of other amino acids, derived from H NMR
data (Fig. 2).
Structure of SbF3 complexes with the amino acids
in the crystal state was relatively complex (Table 1).
1 β-Protons in the β-alanine spectrum.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 5 2014

PROPERTIES OF FLUOROANTIMONATES(III) COMPLEXES
921
Interaction of the SbF3 molecules with organic mole-
(a)
δ, ppm
cules as well as with other antimony(III) fluoride
molecules significantly affected the charge transfer
upon the complexes formation. Low stability of the
complexes in aqueous solutions complicates inter-
pretation of 1H NMR shifts of the complexes.
2
3
EXPERIMENTAL
1
Morphology of the obtained antimony samples was
observed using a EVO-50 XPV scanning electron
microscope (LEO, Germany).
pH
(b)
1H NMR spectra of aqueous solutions of the amino
acids complexes with SbF3 (Table 1) were recorded
using a Bruker Avance 300 spectrometer (room
temperature, рН of 1–6). The chemical shifts δ were
determined with accuracy of ±0.01 ppm and referenced
to sodium 3-(trimethylsilyl)propanesulfonate. The salt
acted as internal reference: 200 mg of the sample was
added to the reference salt solution in deuterated water,
and the spectrum was registered.
δ, ppm
2
1
4
3
Complex fluorine-containing compounds of anti-
mony(III) were prepared starting from the following
substances: antimony(III) fluoride (pure grade),
glycine, β-alanine, DL-serine, DL-valine, L-leucine,
and hydrogen fluoride (all of chemical pure grade),
and L-phenylalanine (Ajinomoto).
pH
(c)
δ, ppm
1
2
The amino acids complexes with SbF3 were
prepared in the aqueous solution at the reactants molar
ratio of 0.5–1 : 1 [8–14]. Purity of the prepared com-
pounds was determined by chemical and X-ray diffrac-
tion studies taking advantage of the standard proce-
dures. X-ray diffraction patterns were recorded using a
Bruker D8 ADVANCE diffractometer (CuKα), the
compounds were identified using the EVA software
and the database of powder diffraction data PDF-2.
4
3
Stability of the prepared complexes in aqueous
solutions was studied with cementation method, in
comparison with antimony trifluoride as well as alkali
metals and ammonium complex fluoroantimonates(III).
pH
Fig. 2. Change of the chemical shift of the NH2CN proton
in the 1Н NMR spectrum. (a): (1) Glycine, Gly; (2)
complex 2SbF3·Gly; (3) complex SbF3·Gly; (b): (1) valine,
Val; (2) complex SbF3·Val; (3) β-alanine, Ala; (4) complex
AlaHSbF4; (c): (1) phenylalanine, Phe; (2) complex
SbF3·Phe; (3) leucine; (4) complex HLeuSbF4.
The cementation method is based on the ability of
more electropositive metal ions to be reduced from the
solution upon interaction with more electronegative
metals [21]. With no external electromotive force, at
the electrode made of the more active metal (for
example, iron with respect to antimony), the less active
metal precipitates from the solution (for the above
example, 2Sb3+ + 3Fe0 → 2Sb0 + 3Fe2+).
In the experiment, we used the electrode made of
St3 steel (20 × 20 × 3 mm) that was polished, washed
with distilled water, and dried in dessicator prior to
use. The electrode was then immersed into aqueous
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ZEMNUKHOVA et al.
10. Udovenko, A.A., Davidovich, R.L., Zemnukhova, L.A.,
Kovaleva, E.V., and Makarenko, N.V., J. Struct. Chem.,
2010, vol. 51, no. 3, p. 540. DOI: 10.1007/s10947-010-
0078-z.
solution (рН 1) of the tested antimony(III) fluorine-
containing compound. In particular, 0.7 g/L of the
studied compound was dissolved in aqueous HCl
(0.1 mol/L) at room temperature. After 20–30 min of
incubation, silver-white precipitate with metal luster
appeared at the electrode surface; X-ray diffraction
study confirmed its identity to metal antimony. The
longest incubation time was of 120 h.
11. Zemnukhova, L.A., Davidovich, R.L., Udovenko, A.A.,
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Zemnukhova, L.A., and Kovaleva, E.V., J. Struct.
Chem., 2010, vol. 51, no. 4, p. 765. DOI: 10.1007/
s10947-010-0113-0.
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