structural and physico-chemical studies of ionic clathrate ... · 1 structural and physico-chemical...
TRANSCRIPT
1
STRUCTURAL AND PHYSICO-CHEMICAL STUDIES OF IONIC
CLATHRATE HYDRATES OF TETRABUTYL– AND
TETRAISOAMYLAMMONIUM SALTS
Andrey Manakov
1, Tatyana Rodionova, Irina Terekhova,
Vladislav Komarov, Alexander Burdin, Artem Sizikov
Nikolaev Institute of Inorganic Chemistry SB RAS
3, Acad. Lavrentieva ave., Novosibirsk, 630090, RUSSIAN FEDERATION
ABSTRACT
This contribution presents short review of resent results of structural and physico-
chemical studies of ionic clathrate hydrates of tetrabutylammonium fluoride, chloride,
bromide, as well as of linear, cross-linked tetrabutylammonium and
tetraisoamylammonium polyacrylates and some double hydrates of these compounds with
methane.
Keywords: ionic clathrate hydrate, tetrabutylammonium salt, tetraisoamylammonium salt,
structure, enthalpy of fusion
1 Corresponding author: Phone: +7 383 316 5346 Fax +7 383 330 9489 E-mail: [email protected]
NOMENCLATURE
CS-I – cubic structure I
SCS-I – superstructure of CS-I
CRPac – cross-linked polyacrylate anion
D cavity – pentagonal dodecahedron (512
)
HS-I – hexagonal structure I
Pac – polyacrylate anion
P cavity - pentakaidecahedron (512
63)
T cavity – tetrakaidecahedron (512
62)
TBA – tetrabutylammonium cation
TiAA – tetraisoamylammonium cation
TS-I – tetragonal structure I
Hf, – enthalpy of fusion
INTRODUCTION
In the crystal structures of ionic clathrate hydrates
of TBA and TiAA halides water molecules and
halide anions form a polyhedral hydrogen bonded
water-anion framework. In the ionic clathrate
hydrates of tetraalkylammonium salts with
carboxylate anions carboxyl group is included in
water framework through its oxygen atoms to form
an edge of a polyhedron whereas hydrophobic part
of the anion occupies a cavity of the water
framework. Butyl and isoamyl groups of the
cations are arranged in polyhedral cavities of this
water-anion host lattice; nitrogen atom of cations
replaces water molecule situated in vertex
common of four neighboring cavities. Host lattices
of ionic clathrate hydrates are structurally related
to those of gas hydrates and can be described as
combination of face-sharing D, T, and P
polyhedra. Hydrocarbon groups of the cations are
located in the T and P cavities, D cavities are
empty [1, 2] (in some cases part of D-cages can be
filled with “guest” water molecules [3-7]). The
structures that are most common of ionic clathrate
hydrates structures are tetragonal structure-I (TS-
I), hexagonal structure-I (HS-I), superstructure of
cubic structure-I (SCS-I) with unit cell
stoichiometry 4P.16T
.10D
.172H2O, 2P
.2T
.3D
.40H2O,
48T.16D
.368H2O, respectively.
It is well known that participation of auxiliary
guest component in hydrate formation in many
cases results in formation of double hydrate with a
higher decomposition temperature [8]. This
method was used for increasing the decomposition
temperature of hydrogen hydrate with use of
auxiliary guest component tetrahydrofuran[9,10].
Practical use of auxiliary guest components faces
some additional requirements. Auxiliary
component must not be lost during formation –
decomposition of the hydrate, it must be produced
in industrial scale, it must be relatively
Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011),
Edinburgh, Scotland, United Kingdom, July 17-21, 2011.
2
inexpensive, etc. Tetraalkylammonium salts are
prospective for use as auxiliary guest component
because they at least partially meet the above
challenge and can serve as promoters of gas
hydrate formation process. At present, ionic
clathrate hydrates of TBA and TiAA salts are the
subject of extensive research stimulated by diverse
possible applications. TBABr polyhydrates were
suggested as cold storage and transportation
material [11,12]. Crystal structures of ionic
clathrate hydrates contain vacant voids suitable for
inclusion of molecules of appropriate sizes, thus
revealing potential for storage, transportation and
separation of gases. It has been found that double
polyhydrates H2-TBAF [13, 14], H2-TBACl [15],
and H2-TBABr [14, 16-18] are formed, which
have better thermal stability (provided equal
pressure) than hydrogen hydrate [19,20] or double
hydrate H2 -THF [9, 16]. It was demonstrated
recently that clathrate hydrate of TBA borohydride
represents a hybrid hydrogen storage material (H2
is produced not only on decomposition of the
clathrate hydrate but also through hydrolysis of the
borohydride ion) [21]. Ionic clathrate hydrates
TBAF [22], TBABr [18, 22-24] are able to form
double hydrates with CO2. It was found quite
recently that ionic clathrate hydrates of TBACl,
TBANO3, and (C4H9)4PBr also form double
hydrates with СО2, which decompose at higher
temperatures (for a given pressure) than pure СО2
hydrate [25]. It was demonstrated that double
hydrates are formed by TBABr with such gases as
methane [18, 26-28], nitrogen [18, 24, 27], and
hydrogen sulfide [27, 29], as well as by TBACl
with methane and nitrogen [15]. Additionally,
hydrates of TBABr appeared to be suitable for
separation of gas mixtures [24, 26, 27, 29, 30].
Single crystal X-Ray structure analysis of hydrate
of TiAABr with krypton and methane confirmed
that the gas molecules are located in the D
cavities; these hydrates are characterized with high
thermal stability [31]. Development of methods of
practical use of tetraalkylammonium salts requires
information on their structures and thermodynamic
properties. However, at present these points are
studied rather poorly. Another interesting point is
formation of double hydrates of tetraalkyl-
ammonium salts with gases in which gas
molecules partially occupy large cavities. It is
necessary to increase gas content in these hydrates.
Unfortunately, no data concerning formation of
such hydrates is available. Thereby, the studies of
the composition and properties of double hydrates
of tetraalkylammonium salts with different gases
is a topical task.
Development of gas hydrate technologies
applicable for gas storage and separation of gas
mixtures is not possible without fast and energy-
sparing industrial-scale synthesis of these
compounds that, consequently, require creation of
large interface between liquid water and a gas. At
present energy-consuming procedures of water
and/or gas dispersion are used to accelerate
reaction of hydrate formation. A possible way to
solve this problem is to use clathrate hydrates that
do not change the aggregate state as they
decompose. The authors of the work [32] suggest
to use hydrate formation within slightly cross-
linked sodium polyacrylate particles swelled in
tetrahydrofuran – H2O solution for storage of H2
gas. Decomposition of clathrate hydrates in such
medium does not cause the change of aggregative
state of the system. Another way that is discussed
in this work consists in using water swellable
clathrate forming polymeric materials. These
materials are slightly cross-linked TBA and TiAA
polyacrylates (carboxylic cationites). The
formation of polyhydrates in swollen grains of
cross-linked TBA and TiAA polyacrylates with
low degree of cross-linking was first revealed in
[33]. Invariable aggregative state of these
compounds in the course of hydrate formation and
decomposition makes studies of these compounds
very interesting.
In this report we present the short review of our
recent structural and physic-chemical studies of
ionic clathrate hydrates of TBA and TiAA salts.
EXPERIMENTAL SECTION The aqueous solutions of TBAF, TBACl, and
TBABr were obtained by neutralizing the TBAOH
solution with corresponding acid and following
recrystallization of polyhydrates from aqueous
solutions. For preparation of cation-exchange
resins in TBA and TiAA forms the carboxylic
cation-exchange resins in the H-form were
neutralized with a 3-fold stoichiometric excess of
0.1N aqueous solutions of TBAOH and TiAAOH,
washed with distilled water and after that were
centrifuged at the same conditions. Aqueous
solution of TiAAOH was synthesized from TiAA
iodide by reaction with Ag2O in water suspension
and purified through the recrystallization of a
clathrate hydrate. Polyacrylic acid with average
molecular mass of 1800 daltons (Aldrich) without
further purification and tetraisoamylammonium
3
hydroxide solution were used to prepare TBA and
TiAA salt of the linear (unlinked) polymeric
anion. Methane gas with a purity not less than
99.9% and distilled water were used in
experiments. The content of TBA (TiAA) cations
was measured by potentiometric titration with a
sodium tetraphenylborate solution using an ion-
selective electrode. Samples of the double hydrates
of TBA salts with methane were prepared in
reaction of powdered crystals of TBA salts with
compressed methane in autoclave. The synthesis
was continued for 2-3 weeks to complete the
reaction.
Single crystals of ionic clathrate hydrates of
TBAF, TBACl, TBABr and TBAPac with
different hydrate numbers were prepared by
cooling and holding of aqueous solutions with
different concentrations in the home-made air
thermostat for a span varying from a few hours to
a few days. These crystals were used for
measurement of enthalpies of fusion and X-ray
diffraction experiments. The crystals were
separated from the solutions and quickly dried
between two sheets of filtering paper up to air-dry
state. All procedures were conducted in the air
thermostat at the temperature of the crystal
growth. A portion of the crystals was further
placed into flask for analytical determination of
the hydrate composition, the other portion was
simultaneously used for calorimetric and X-ray
experiments.
A differential scanning calorimeter DSC-111
(Setaram) was used for determination of enthalpies
of fusion. The samples of hydrates were sealed up
in 0.1 ml steel pans for calorimetric studies of
enthalpies of fusion. 5-8 measurements were
carried out for each of the hydrates. Samples
weight varied from 0.03 to 0.09 g. Measurements
were carried out at heating rate of 0.5oC/min. The
observed heats of fusion were normalized by
electric calibration provided by the manufacturer.
Single-crystal diffraction experiments were
conducted at 150±1 K on a Bruker X8 APEX CCD
diffractometer with MoK radiation [34]. X-Ray
powder diffraction studies were performed at –
20oC on a Bruker D8 Advance diffractometer
(CuK radiation, = 1.5418 Å) equipped with
Anton Paar refrigerating device. Phase diagrams
were investigated by DTA at high pressure; high-
pressure equipment has been described in [35].
Pressure was measured with precise gauge (0.25%
hydrate number,
(m.p.,oC)
Hf, kJ/mol hydrate
(kJ/mol H2O)
Ref.
TBAF hydrates
30.22 (25.0) 197.16 (6.52) [38]
30.0 (28.3) 184±4 [39]
32.44 (27.2) 203.0±2.3(6.26) [40]
28.94 174.3±3.1(6.03) [40]
TBACl hydrates
32.24 (15.0) 4.9 (5.56) [41]
29.74 (15.1) 156.9 .1 (5.28) [41]
30.0 (15.0) 156 [39,42]
30.0 (15.2) 164.1 (5.47) [43]
30.0 173.6 (5.79) [25]
24.83 (14.9) 127.9 .6 (5.16) [41]
TBABr hydrates
38.0 (9.9) 200.98±5.32 ( 5.29) [12]
38.13 (9.7) 219.4 .9 (5.76) [this work]
32.53 (12.0) 177.2 .5 (5.45) [this work]
26 (12.0) 152.76±6.74 (5.88) [12]
26 151.9 (5.84 ) [24]
26.46 (12.0) 150.7 .1 (5.71) [this work]
24.04 (12.3) 136.2 .1 (5.68) [this work]
Table 1. The stoichiometry, melting points, and
the enthalpies of fusion of the TBAF, TBACl and
TBABr polyhydrates.
error). Temperature was measured with a
Chromel-Alumel thermocouple with precision of
0.2oC. The release of gas from the studied samples
was monitored as a function of temperature by
collecting the gas into a calibrated burette placed
into a concentrated aqueous NaCl solution [36].
RESULTS AND DISCUSSION
Calorimetric studies of TBAF, TBACl, and
TBABr ionic clathrate hydrates. Our results of determination of the compositions
and enthalpies of fusion of TBAF, TBACl, TBABr
ionic clathrate hydrates are listed together with the
data available from the literature in Table 1.
Crystal structures
The crystal structure of TBAF.29.7H2O ionic
clathrate hydrate. The study of TBAF – H2O [37]
phase diagram revealed formation of two hydrates:
TBAF.32.4H2O (TS-I, [5]) and TBAF
.28.6H2O.
We have determined crystal structure of
TBAF.28.6H2O hydrate [6]. Idealized water
framework is isostructural with CS-I of gas
hydrates but with eight-fold unit cell (SCS-I, I-
43d, a=24.375(3)Å). Positions of fluoride-anions
4
Figure 1. The arrangement of TBA cation of
TBAF within 4T cavity; (b) the inclusion of
“guest” water molecule (O11) in distorted D
cavity.
Figure 2. (a) 4T combined cavity, (b) 3TP
combined cavity, (c) location of TBA of TBACl
cation within 3TP cavity.
Figure 3. Two modes of hydrophylic inclusion of
chloride anion of TBACl: (a) with displacement
of one hydrogen bonded water molecule of host
framework (oxygen atom O2 is substituted by
Cl2), and (b) with displacement of two water
molecules (pair O11-O12 is substituted by Cl1).
are not localized. Nitrogen atom of the cation
occupies the common vertex formed by four face-
sharing T polyhedra forming combined 4T cavity
(Fig.1a); hydrocarbon chains fill compartments of
this cavity. Inclusion of the cation results in
“pressed in” of some framework water molecules
in D-cavities which are partially filled by “guest”
water molecules with the filling degree 79.5 %
(Fig.1b). With this in mind the calculated hydrate
number 29.7 is greater than predicted by idealized
water framework 28.7.
The crystal structures of TBACl ionic clathrate
hydrates. T,X phase diagram of the TBACl – H2O
binary system and the solubility isotherm (8oC) of
TBACl – NH4Cl – H2O ternary system have been
studied in our laboratory by DTA and
Schreinemakers' method, respectively [44]. It was
shown that three ionic clathrate hydrates
TBACl.nH2O (n=32.2, 29.4, 24.1) form in this
system. We carried out the X-ray diffraction
experiments for four single crystals with the
stoichiometry TBACl*nН2О (n=·32.7(s1); n=30.4
(s2); n=·30.1(s3); n=
·27.4(s4)). It was shown that
all of them belong to space group P42/m
corresponding to idealized host water framework
TS-I, the unit cells dimentions, Å: a=23.571(11),
c= 12.4361(6); a=23.5818(12), c=12.4148(7);
a=23.5281(15), c=12.4918(7); a=23.4881(44),
c=12.5289(21), respectively. All structures
resemble the structure of ionic clathrate hydrate
TBAF.32.8H2O [5]. TBA cations are located in
four-compartment cavities of two types: 4T and
3TP (Fig.2). Chloride ions are included in the
hydrate framework, two inclusion modes being
found (Fig.3): (1) substitution of one water
molecule of the host framework; (2) substitution
of two hydrogen-bonded water molecules. Due to
distortion of the host framework induced by
inclusion of TBA cations, some of D-cavities have
three “pressed in” vertices and residual electron
density peaks within the cavities. This electron
density was refined as oxygen atoms of included
guest water molecule.
The comparison of pairwise Rint(i, j) statistics
indicates that the intensity data arrays can be
divided in two groups: s1, s2 and s3, s4. The most
distinct differences between the groups s1, s2 and
s3, s4 are manifested in details of the structural
models (site occupation factors, positions and
values of residual electron density peaks) obtained
on structure solution. The major dissimilarities
appear in occupation factors of chloride-ion
positions and atomic displacement parameters of
oxygen atoms of the host framework. Significant
differences are also observed in positions of
residual electron density peaks. Two of them are
inside the T-voids involved in formation of the 4T
cavities, and another two are inside the D-voids
adjacent to these T-cavities. The last four electron
density peaks are considerably separated from the
host framework atoms and, apparently, indicate
the inclusion of TBA cations in combined cavities
involving D-voids. Correct structural model
describing disordering in these crystals is, most
likely, quite complicated and we have not
succeeded yet in elaborating it. The data obtained
suggest the formation of two phases of ionic
clathrate hydrates of tetrabutylammonium
chloride, both having TS-I but differing in
5
Figure 4. Powder diffraction patterns of
TBACl·nH2O in 2θ range 5 to 25o.
stoichiometry. The total of the data obtained on the
compositions of the hydrates indicates that the
stoichiometry of crystals s1, s2 is, most likely,
close to TBACl·32Н2О, while for s3, s4 - to
TBACl·30Н2О. The occurrence of only two
different hydrates in four experiments suggests the
absence of continuous solid-state solubility in the
studied concentration range.
In order to confirm the existence of hydrates with
stoichiometry close to TBACl·32Н2О,
TBACl·30Н2О, TBACl·24Н2О and unit cell
similar to that of TS-I, X-ray powder diffraction
study of three samples of hydrate phases has been
carried out. The chemical analysis of the
composition of the representative probes taken
from the samples revealed hydrate numbers
n=32.2, 29.7, 24.8 (TBACl·nH2O). In all three
cases the diffraction patterns obtained are quite
similar (Fig.4). We calculated positions of
diffraction peaks expected for a TS-I hydrate
possessing the highest symmetry P42 /m known for
this type of hydrates. All reflections observed in
this range can be interpreted in the framework of
TS-I structural model with P42/m symmetry. These
results support the hypothesis about the presence
of several hydrates having different compositions
but the same TS-I unit cell.
The crystal structure of TBABr ionic clathrate
hydrates. There are different data on the number of
ionic clathrate hydrates and their stoichiometry in
TBABr – H2O binary system [12,39,45,46]. Our
data on examination of T,X phase diagram of the
TBABr – H2O system and of solubility isotherms
of TBABr – third component – H2O systems
indicated the occurrence of four ionic clathrate
hydrates: TBABr·nH2O (n=36, 32, 26, 24) [46].
With regard to structural characteristics the only
Figure 5. The arrangement of pair of TBA cations
of TBABr within eight-compartment 4D4T
cavity.
a b
Figure 6. Br− in tetrahedral (a) and square
pyramidal (b) coordination .
structure of orthorhombic TBABr·38H2O is known
at present [47]. We carried out a single crystal X-
ray structure analysis of hydrate TBABr·24H2O.
The structure was solved by the direct method.
The structure of host water framework is TS-I,
space group is P-4 with unit cell dimensions
a=23.492(3)Å, c=38.021(8)Å, structural hydrate
number is 24.8÷25.7. Two manners of inclusion of
TBA cations were revealed: (1) arrangement of
one TBA cation in four compartment 3TP cavity,
and (2) insertion of two TBA cations in eight-
compartment 4D4T cavity (Fig.5). Probably, the
latter peculiarity is responsible for existence of
several hydrates of TS-I in the same system and
was not known until now. In addition, a previously
unknown way of hydrophilic inclusion of Brˉ in
the host water framework is found. Brˉ is
coordinated by four water molecules so that it is
situated on the top of a square pyramid (Fig.6). An
occurrence of superstructure (triple c parameter) is
apparently caused by minimization of distortions
of hydrogen bond network of water anion host
framework arising from formation of eight-
compartment cavities.
Phase diagrams, structural and calorimetric
studies of the polyhydrates of linear and cross-
linked TBA and TiAA polyacrylates
We studied phase diagrams of the binary systems
water – cross-linked TiAACRPac (0,5-3% cross-
linking) [48], water – TBACRPac (1% cross-
linking). The phase diagrams studies were also
6
n, (m.p.,oC),
Hf, kJ/mol hydrate
(kJ/mol H2O)
Ref.
Hexagonal, P-6m2, a=12.15, c =12.58 Å (100 K)
a=12.26, c =12.71 Å (276 K) [50]
40.8 (18.4),
=0%
218.8 4.5 (5.36)
[54]
Hexagonal, a=12.25, c=12.72 Å (276 K) [49]
37.7 (15.5),
=0.5%
193.0 2,3 (5.12)
[54]
37.6 (14.6),
=1.0%
189.1 2.3 (5.03)
[54]
33.5 (13.7),
=2.0%
158.8 2.3 (4.74)
[54]
29.7 (13.0),
=3.0%
123.9 6.2 (4.17) [54]
Table 2. Properties of the hydrates of linear and
cross-linked tetraisoamylammonium polyacrylates
with different degrees of cross-linking ( = 0 –
3%). n – hydrate number (for the hydrates of the
polymeric salts the hydration number given is the
number of water molecules per the elementary unit
of the polymeric chain, taken from Ref. [48]). m.p.
– melting point.
n, (m.p.,oC),
Hf, kJ/mol hydrate
(kJ/mol H2O)
Ref.
monoclinic, 2/m, a=23,456 Å, b =12.327 Å
c = 23,454 Å, = 90,040
(150 K), a=23,60 Å, c =12,40
Å (248 K)
33.23 0,27
(13.2), =0%
157,1 2.7 (4,74) this
work
tetragonal, a=23.471 Å, c=12.328 Å (150 K)
31.62 0,31
(15.0), =0%
this
work
tetragonal, a=23.436 Å, c=12.330 Å (150 K)
30.04 0,31
(15.0), =0%
this
work
tetragonal, a=23.425 Å, c=12.364 Å (150 K)
a=23.58 Å, c=12.41 Å (248 K)
28.43 0,09
(17.5), =0%
130,8 6.8 (4.60) this
work
tetragonal, a=23.56 Å, c=12.37 Å (248 K) 29.9 (8.5),
=1% 128,9 3.0 (4,31) this
work
tetragonal, a=23.61 Å, c=12.40 Å (248 K) 26.5 (8.5),
=1% 119,2 4.2 (4,50) this
work
Table 3. Properties of the hydrates of linear and
cross-linked tetrabutylammonium polyacrylates
with cross-linking = 1%. n – hydrate number (for the hydrates of the polymeric salts the
hydration number given is the number of water
molecules per the elementary unit of the polymeric
chain). m.p. – melting point.
Figure 7. Phase diagrams of the binary
systems: (a) water – cross-linked TBACRPac
(cross-linking 1%) and (b) water – cross-linked
TiAACRPac (cross-linking 1%) in the region of
clathrate hydrate formation.
carried out with salts of liniar polymers. Obtained
information concerning compositions, melting
temperatures, structures and enthalpies of fusion is
summarized in Tables 2,3. The graphical
representation of phase diagrams is given in the
Fig.7.
The results of X-ray powder diffraction studies of
1, 2 and 3% cross-linked TiAACRPac hydrates
[49] and those of cross- linked (1% cross-linking)
TBACRPac revealed the existence of a crystalline
hydrate phase in frozen swollen grains of the
studied resins. It was shown that all TiAA hydrates
are hexagonal with the unit cell parameters (Table
2) corresponding well to HS-I. Polyhydrates of
cross-linked TBACRPac are tetragonal with the
unit cell parameters (Table 3) that suit well to TS-
1. Both structures are characteristic of many
clathrate hydrates of TBA and TiAA salts [1]. The
hydrate crystallites inside the grains are relatively
large, up to 0.01 mm3; each grain contains 100-200
crystallites.
It is not possible to obtain single crystals of
hydrates of cross-linked polymeric carboxylates
hence precise determination of their crystal
structure is also impossible. Therefore, a hydrate
with linear polyacrylates of TBA and TiAA were
attempted as a first model approximation. The
validity of this approach was demonstrated by the
comparison of powder X-ray diffraction patterns
of the samples of the polyhydrates with linear
polymers with those of cross-linked TiAA and
TBA polymers that revealed the identity of the
crystal structures (Fig.8,9, Tables 2,3).
Phase diagram of the binary system water –
tetraisoamylammonium polyacrylate (un-cross-
linked) was determined using DTA method. Only
one compound forms in the studied concentration
range with the melting point of +18.4oC. The
compound was isolated as a crystalline product
7
Figure 8. Powder diffraction patterns of the
polyhydrates of linear (f) and cross-linked (1%,
2%, 3%) TiAACRPac (a-d), recorded at 3 10C
and those (e) recorded at room temperature (200C);
c,d – 3% degree of cross-linking when using teflon
(c) and lavsan (d) coating films.
Figure 9. Powder diffraction patterns of the
polyhydrates of linear (lower pattern ) and cross-
linked (1%) TBA polyacrylates (upper pattern),
recorded at -250C.
and analyzed (six independent determinations) to
give the composition TiAAPac·(40.8 0.5)H2O
(Table 2). The single crystal X-ray analysis of the
hydrate of this compound [50] confirms its
clathrate nature. The hydrate crystal was
hexagonal; the unit cell dimensions refined using
all data were a = 12.150(1), c = 12.580(1) Å (at
100 K). In the crystal structure, the water
molecules form a 3-D hydrogen-bonded host
framework which is distorted variant of HS-I. The
Figure 10. (a) the layer of face-sharing 15-hedral
(P) polyhedra at the z~0 level and one of
combined 4-sectioned cavities (P2T2, outlined with
bold lines). (b) The layer of face-sharing 12-hedral
(D) polyhedra at the z~0.5 level.
space group is P-6m2. The large P polyhedra are
located in a layer at the z~0 level sharing their
hexagonal faces (each P polyhedron has three
hexagonal faces) and producing a honey-comb
system (Fig.10a). Each hole is filled with two T
polyhedra on both sides of the layer; the T cavities
stack on top of each other producing columns
along the c axis. The next layer, at z~0.5, is filled
with D polyhedra sharing their pentagonal faces
(Fig.10b). All the large cavities are occupied by
the hydrophobic alkyl groups of TiAA cation
which is included in 2P2T four-compartment
cavity. Similar inclusion mode was observed in
previously reported clathrate hydrates with this
cation[51,52] and is consistent with the ability of
the isoamyl fragment to fit only in a large cavity
but not in a small one. The cations are situated in
layers at z~0 level (Fig.10a). The crystal,
therefore, has a pseudo-layered organization with
respect to the location of guest. According to our
structural model the chains of polyacrylate anion
can only be located within the layer of D-
polyhedra at z~0.5 (see Fig.10b). The location of
the chains is impossible to find directly from the
experiment due to a great number of possible
positions that produces a multi-fold disorder from
the viewpoint of crystallography.
There is no doubt that the incorporation of the
carboxylate groups of the polymeric chain occurs
as a hydrophilic inclusion, as it was observed for
tetraalkylammonium salts of monomeric
carboxylates [3,7,51]. In other words, the two O
atoms of the carboxylate group replace two
adjacent O atoms in the polyhedron. At the same
time, the incorporation of the main hydrocarbon
chain of the polymer in the layer of undistorted D-
polyhedra is not feasible because the D polyhedra
do not have "windows" of sufficient size. One
could assume that the local microenvironment
around the chain is distorted in such a way that the
8
D-polyhedra form a channel. The formation of
such channels requires energetically unfavorable
distortion of the hydrate framework. The
parameters of the polyacrylate main chain should
be similar to those of polyethylene for which the
translational period of 2.54 Å is expected. Taking
the shortest dimension of the hydrate unit cell,
12.15 Å, at least five polyacrylate monomers
should fit in a single unit cell through which the
polymeric chain would run, producing a negative
charge far greater than it is necessary to balance
the 1+ charge of the cation (HS-I hydrates contain
1 cation per unit cell). Therefore, there is
excessive space for the accommodation of the
polyanion, most unit cells do not host the polymer
at all, and the concentration of local distortions
induced by the anion inclusion is relatively low. In
addition, there are several ways of how the chain
may enter and exit the unit cell (cf. Fig.10b) and
so the accommodation of the polyanion is very
favorable in terms of entropy. The described above
inclusion of the polyanion should create high local
concentrations of negative charge in the structure
which would be very unfavorable in terms of
enthalpy. Partially the loss is compensated by the
entropy term. However, the transfer of a proton
from the host hydrate framework to carboxylate
group is very probable here. The residual hydroxyl
anions may be located near the positively charged
nitrogen atoms of the cation. In conclusion, it
should be noted that the observed layered
organization of the structure explains the
possibility of inclusion in the crystal of cross-
linked polyacrylate. The availability of excessive
space within the D-layer and high freedom for the
polymeric chain accommodation facilitate the
inclusion. The chain can change direction at every
3D-intersection as evident from Fig.10b. The
accommodation would be more difficult within a
channel structure as one reported for TBAPac
[53]. According to the above results, most D-
cavities in the hydrates are vacant from the main
guest. This available cavity space may be utilized
for accommodating an auxiliary guest.
In order to characterize the hydrate phases
crystallized in the system water – TBAPac single-
crystal X-ray diffraction studies were performed
for four polyhydrates formed in the system
according to phase diagrams studies and analytical
determination of the compositions of the hydrates.
Unit cell parameters of all crystals studied are
similar and vary in the ranges
(a≈b=23.42÷23.48Å, c=12.33÷12.37Å), the angles
are close to 90° (Table 3). It was found in the
course of the statistical analysis of hklF – data that
the crystals of three studied polyhydrates have
Laue class 4/m, the values of Rint indices vary from
0.024 to 0.062, the symmetry of the diffraction
picture for the crystal of fourth hydrate is lower
and is characterized with Laue class 2/m
(Rint=0.057). The structural models obtained show
that the studied hydrates have the crystalline water
frameworks related to the TS-1. Because of the
significant disordering in the guest and partially in
the host subsystems the structure cannot be
described in detail. It can be said, however, that
the cations of the polymeric guest are included in
the combined 3TP и 4T cavities in the structure.
Besides, the presence of the electronic density in
all symmetrically independent D cavities of the
framework can be associated with the
accommodation of the polyacrylate anion inside
the cavities.
The calorimetric studies of the polyhydrates of
TBA and TiAA polyacrylates
The heats of fusion were measured for the
clathrate hydrates comprising linear and cross-
linked TBACRPac (cross-linking degree 1%) and
TiAACRPac (cross-linking degree 0,5-3%) [54]. It
should be noted that no data on clathrate formation
thermodynamics for any tetraalkylammonium salts
with cross-linked polymeric anions could be found
in the literature, while only some data on fusion
enthalpies of the hydrates with linear TBA and
TiAA polyacrylates have been reported by
Nakayama [55]. The results of the calorimetric
measurements are presented in Table 2,3. It is seen
from the calorimetric data that cross-links in
polymeric anion cause the decrease in the fusion
enthalpies of the polyhydrates with cross-linked
polymeric guests in comparison with those of the
polyhydrates with linear polymers. For the
polyhydrates of TiAA cross-linked polyacrylates it
was shown [54] that both the fusion enthalpy and
composition of the hydrates of TiAA polyacrylate
are linear functions of the degree of cross-linking
of the guest polymeric anion included in the
hydrate framework.
Double ionic clathrate hydrates with gases
TBABr – methane – water system. We studied
decomposition curves of double TBABr - methane
hydrate formed by aqueous solutions of TBABr
with 1:38 (31.7 mass.%) and 1:81.5 (18 mass.%)
TBABr to H2O molar ratio and excess of gaseous
9
Figure 11. Decomposition curves of HS-I hydrate
TBABr*38H2O, double hydrate TBABr*
38H2O+CH4 and hydrate phases formed by
aqueous solution of TBABr (1:81.5 TBABr:H2O
molar ratio) with methane.
a
b
Figure 12. Effect of pressure on the decomposition
points for (a) TBACRPac hydrate (0.5%): without
hydrogen (A); under pressure of hydrogen (B); (b)
TiAACRPac hydrate (2%): without hydrogen
addition (A); under pressure of hydrogen (B).
methane. Some experimental data which were
obtained in these experiments are shown in Fig.11.
1:38 TBABr solution corresponds to
stoichiometric ratio TBABr and water which was
expected for double hydrate with the HS-I. On the
basis of this information we attribute DTA effects
corresponding to this solution to decomposition of
double hydrate (Fig.11). In the case of 1:81.5
solution the situation was more complex (Fig.11).
In addition to DTA effects corresponding to
decomposition of double hydrate, 2 groups of
DTA effects occur. Low-temperature group of
weak effects at temperature close to 0oC
correspond to melting of aqueous eutectic.
Positions of the second group of DTA effects
coincide with decomposition curve of methane
hydrate. This hydrate was undoubtedly formed by
aqueous eutectic and excess of methane gas.
Temperature of methane hydrate decomposition in
this case was not changed because aqueous
eutectic in the TBABr-H2O system represent itself
almost pure water [40].
Double hydrates with cross-linked polyacrylates.
The P,T curves of hydrate decomposition in the
systems TBACRPac (0.5% cross-linking) – H2O
and TiAACRPac (2% cross-linking) – H2O, along
with the decomposition curves of these hydrates
under a pressure of hydrogen, are presented in
Fig.12. The melting curves for the hydrates of pure
ion-exchange resins contain fractures (P = 46 MPa
for TiAACRPac hydrate and P = 65 MPa for
TBACRPac hydrate), which probably suggest the
formation of new hydrate phases at these
pressures. A considerable increase in hydrate
decomposition temperatures is observed in both
cases upon imposition of hydrogen pressure over
the entire pressure range. Furthermore, no
characteristic fractures on the curves were
observed; the scatter of experimental points is
within the experimental error. A similar picture is
typical of the formation of double hydrates, i.e. the
structures of TBACRPac and TiAACRPac
hydrates contain vacant cavities; filling of the
latter with hydrogen molecules increases their
decomposition temperatures. It should also be
noted that the specimens had the form of solid
granules both before and after the experiment.
The experiments discussed above has shown that
(1) reaction of methane with 18 mass.% solution
of TBABr results in mixture of double hydrate and
gas hydrate of pure methane, (2) cross-linked
TiAACRPac and TBACRPac can form the double
10
Figure 13. Typical curves of gas emission. For
comments see the text
experiment V V1 V2
11 103.6 81.4 22.2
21 103.2 81.7 21.5
32 42.0 28.2 13.8
42 34.5 22.1 12.4
Table 4. Volumes of gas emitted at 1-st and 2-d
steps of decomposition of the samples of double
hydrates with methane. 1 double hydrate was
formed by18 mass.% solution of TBABr (1 : 81.5
TBABr :water molar ratio); 2 double hydrate was
formed by cross-linked polyacrilat of TBA, 80%
substitution of H+ to TBA+ cations; 78 mass.%
content of water
hydrates. We plan to perform the series of
experiments aimed in determination of
composition of these hydrates. Here we present the
first results of this work. In all of these
experiments we used row samples with TBA :
water molar ratio below that characteristic of
respective hydrates (Tables 1-3). We suppose that
row samples of this type are most appropriate to
obtain double hydrates with partial occupation of
large cavities with methane molecules and,
consequently, with high content of gas. Samples
for these experiments were synthesized in
autoclaves (see Experimental section). The
autoclaves were discharged at the liquid nitrogen
temperature; volume of gas emitted from the
samples in the temperature range from liquid
nitrogen to room temperature was measured as
function of temperature at atmospheric pressure.
Typical experimental curves are shown in Figure
13, numerical results of the experiments are
presented in Table 4. In all cases two steps of the
gas emission occurs. Temperature of the first step
(V1 in Table 4) roughly corresponds to
decomposition temperature expected for methane
hydrate at atmospheric pressure. The second step
we attribute to decomposition of double hydrates.
Assuming 100% transformation of TBA cation to
the double hydrate and that TBA : water molar
ratio in the double hydrates is equal to what in the
hydrates of pure TBA
salts we determined
compositions of the TBABr+CH4 double hydrate
as TBABr·(1.7-1.8)CH4·38H2O and TBACRPac+
CH4 double hydrate as TBAPac·(0.8-0.9)CH4·
26.5H2O. The compositions expected for 100%
occupation of small D-cavities with methane are
TBABr·3CH4·38H2O and TBAPac·2CH4·26.5H2O,
respectively. Taking into account that composition
of methane hydrate is close to CH4·6H2O we can
calculate quantity of the methane hydrate
decomposed at the first step of the process and,
consequently, to calculate quantity of non-reacted
water in each experiment. The samples with
TBABr contained about 5.5 % of the initial water
content was not transformed to hydrate. In the case
of cross-linked polyacrilates quantity of non-
reacted water was higher (40-45% of water
available for hydrate formation). molecules.
Concluding remarks
The most interesting and unexpected result of this
work is formation of several ionic clathrate
hydrates with the same water framework (TS-I),
almost undistinguishable parameters of the unit
cell but significantly different compositions.
Hydrates of this type occurred in the systems
water - TBABr, TBACl and TBAPac. We
speculate that formation of these hydrates is result
of the compromise between the tendencies to the
closest filling of crystal structure with atoms and
molecules, to formation of phases with highest
entropy, and to form hydrate framework with
undistorted hydrogen bonds. In the case of hydrate
11
formation in the diluted (in comparison with the
hydrate compositions) solutions of TBACl and
TBABr the hydrates with the smallest distortion of
hydrate framework form. In these hydrates
occupation degree of small D-cavities with guest
component is zero or minimal. Crystallization of
ionic clathrate hydrates from solutions with higher
guest concentration results in the formation of
hydrates with high content of occupied 3DT and
4T4D cavities and smaller hydrate numbers. In
this case more dense packing of the hydrate
framework is caused by partial occupation of small
D-cavities with alkyl radicals of TBA cation.
Formation of the hydrates with dense packing of
crystal structure requires distortion of hydrate
framework, e.g. in these frameworks coordination
of some anions with water molecules is pyramidal
instead of tetragonal. We believe that entropy of
these hydrates is higher in comparison with the
hydrates with lager hydrate numbers. The factors
considered above result in systematic decrease of
specific enthalpy of hydrate fusion with decrease
of hydrate number of the respective ionic clathrate
hydrates (Table 1). We suppose that the formation
of several TS-I hydrates by cross-linked TBA
polyacrylates is caused by the same peculiarities of
the crystal structures. Further work is necessary to
prove this idea. Some other peculiarities of the
studied hydrates should be mentioned. First of all
the formation of several hydrates in one system
with the same structural type but significantly
different compositions is possible only for TBA
salts. No examples of this type are known for
TiAA hydrates. Most probably, the size of butyl
group allows it to occupy small D-cavity with
minimal distortion of the hydrate framework that
is not possible for isoamyl group. The second
interesting observation is that hydrates of this type
form in the systems with the anion distorting
hydrate framework (Cl-, Br
- but not F
-) or even
destroying it (cross-linked polyacrylates).
Probably, weakening of hydrogen bonds in
hydrate framework makes possible structural
modernization of this framework without change
of the type of this framework. Finally, the results
concerning formation of double hydrates of
TBABr and cross-linked polyacrylates of TBA
with methane show that substitution of TBA cation
with methane is unlikely. In all cases the samples
obtained after reaction of the row samples with
methane contained not only double hydrate, but
also gas hydrate of pure methane. We speculate
that the formation of two types of gas hydrates is
more favorable energetically in comparison with
formation of double hydrates with partial
occupation of large cavities with methane.
ACKNOWLEDGMENTS
We acknowledge financial support from Russian
Foundation of Basic Research (Grant 09-03-
00367) and Siberian Branch of Russian Academy
of Science (Integration project “Fundamental
aspects of Physical Chemistry of Gas Hydrates:
Research for Practical Use”)
REFERENCES
[1] Jeffrey GA. Hydrate inclusion compounds. In:
Atwood JL, Davies JE, MacNicol DD, Vogtle F,
editors. Comprehensive Supramolecular Chemistry.
Oxford: Pergamon, 1996. v.6. ch. 23, p.757-788.
[2] Dyadin YuA, Udachin KA. Clathrate Polyhydrates
of Peralkylonium Salts and Their Analogs. J.Struct.
Chem. 1987;28:394-432.
[3] Bonamico M, Jeffrey GA, McMullan RK.
Polyhedral Clathrate Hydrate. III. Structure of the
Tetra n-Butyl Ammonium Benzoate Hydrate. J. Chem.
Phys. 1962;37:2219-2231.
[4] Jeffrey GA, McMullan RK. Polyhedral Clathrate
Hydrate. IV. The Structure of the Tri n-Butyl Sulfonium
Fluoride Hydrate. J. Chem. Phys. 1962;37:2231-2239.
[5] McMullan RK., Bonamico M, Jeffrey GA.
Polyhedral Clathrate Hydrate. V. Structure of the
Tetra- n-butyl Ammonium Fluoride Hydrate. J. Chem.
Phys. 1963;39:3295-3310.
[6] Komarov VYu, Rodionova TV, Terekhova IS,
Kuratieva NV. The cubic superstructure – I
of tetrabutylammonium fluoride (C4H9)4NF·29.7H2O
clathrate hydrate. J. Incl. Phenom. Macrocycl. Chem.
2007;59:11-15.
[7] Rodionova TV, Komarov VYu, Lipkowski J,
Kuratieva NV. The structure of the ionic clathrate
hydrate of tetrabutylammonium valerate
(C4H9)4NC4H9CO2.39.8H2O. New J. Chem. 2010;
34:432 – 438.
[8] Glew DN, Mak HD, Rath NS. Aqueous non-
electrolyte solutions: Part VII. Water shell stabilization
by interstitial nonelectrolites. In: Covinston A.K. and
Jones P., editors. Hydrogen-Bonded Solvent Systems.
London: Taylor and Francis LTD, 1968, p.185-193.
[9] Florusse LJ, Peters CJ, Schoonman J, Hester KC,
Koh CA, Dec SF, Marsh KN, Sloan ED. Stable Low-
Pressure Hydrogen Clusters Stored in a Binary
Clathrate Hydrate. Science 2004; 306: 469-471.
[10] Lee H, Lee J, Kim DY, Park J, Seo Yu, Zeng H,
Moudrakovski IL, Ratcliffe CI, Ripmeester JA. Tuning
clathrate hydrates for hydrogen storage. Nature 2005;
434: 743-744.
[11] Darbouret M, Cournil M, Herri JM. Rheological
study of TBAB hydrate slurries as secondary two-phase
12
refrigerants. Int. J. Refrig.-Rev. Int. Froid. 2005;
28(5):663-671.
[12] Oyama H, Shimada W, Ebinuma T, Kamata Y,
Takeya S, Uchida T, Nagao J, Narita H. Phase
diagram, latent heat, and specific heat of TBAB
semiclathrate hydrate crystals. Fluid Phase Equilibria.
2005;234:131-135.
[13] Sakamoto J, Hashimoto S, Tsuda T, Sugahara T,
Inoue Y, Ohgaki K. Thermodynamic and Raman
spectroscopic studies on hydrogen + tetra-n-
butylammonium fluoride semi-clathrate hydrates.
Chem. Eng. Sci. 2008;63:5789-5794.
[14] Chapoy A, Anderson R, Tohidi B. Low-Pressure
Molecular Hydrogen Storage in Semi-clathrate
Hydrates of Quaternary Ammonium Compounds.
J.Am.Chem.Soc. 2007;129:746-747
[15] Makino T, Yamamoto T, Nagata K, Sakamoto H,
Hashimoto S, Sugahara T, Ohgaki K. Thermodynamic
Stabilities of Tetra-n-Butylammonium chloride +H2,
N2, CH4, CO2 or C2H6 Semiclathrate Hydrate Systems.
J. Chem. Eng. Data 2010;55:839-841.
[16] Hashimoto S, Murayama S, Sugahara T, Sato H,
Ohgaki K. Thermodynamic and Raman spectroscopic
studies on H2 + tetrahydrofuran +water and H2 +
tetra-n-butylammonium bromide + water mixtures
containing gas hydrates. Chem. Eng. Sci.
2006;61:7884-7888.
[17] Hashimoto S, Sugahara T, Moritoki M, Sato H,
Ohgaki K. Thermodynamic stability of hydrogen +
tetra-n-butylammonium bromide mixed gas hydrate in
nonstoichiometric aqueous solutions. Chem. Eng. Sci.
2008;63:1092-1097.
[18] Arjmandi M, Chapoy A, Tohidi B. Equilibrium
Data of Hydrogen, Methane, Nitrogen, Carbon
Dioxide, and Natural Gas in Semi-Clathrate Hydrates
of Tetrabutylammonium Bromide. J. Chem. Eng. Data
2007;52:2153-2158.
[19] Dyadin YuA, Larionov EG, Aladko EYa,
Manakov AYu, Zhurko FV, Mikina TV, Komarov
VYu, Grachev EV. Clathrate formation in water-noble
gas (hydrogen) systems at high pressures. J. Struct.
Chem. 1999;40:790-795.
[20] Dyadin YuA, Larionov EG, Manakov AYu,
Zhurko FV, Aladko EYa, MikinaTV, Komarov VYu.
Clathrate Hydrates of Hydrogen and Neon.
Mend.Comm. 1999;209-210.
[21] Shin K, Kim Y, Strobel TA, Prasad PSR, Sugahara
T, Lee H, Sloan ED, Sum AK, Koh CA. Tetra-n-
butylammonium Borohydride Semiclathrate: A Hybrid
Material for Hydrogen Storage. J. Phys. Chem. A.
2009;113:6415-6418.
[22] Fan S, Li S, Wang J, Lang X, Wang Y. Efficient
Capture of CO2 from Simulated Flue Gas by Formation
of TBAB or TBAF Semiclathrate Hydrates. Energy &
Fuels. 2009;23:4202-4208.
[23] Lin W, Delahaye A, Fournaison L. Phase
equilibrium and dissociation enthalpy for semi-
clathrate hydrate of CO2 + TBAB. Fluid Phase
Equilbria. 2008;264:220-227.
[24] Deschamps J, Dalmazzone D. Dissociation
enthalpies and phase equilibrium for TBAB semi-
clathrate hydrates of N2, CO2, N2+CO2, CH4+CO2.
J.Therm.Anal.Cal. 2009;98:113-118.
[25] Mayoufi N, Dalmazzone D, Fűrst W, Dalahaye A,
Fournaison L. CO2 Enclathration in Hydrates of
Peralkyl-(Ammonium/Phosphonium) Salts: Stability
Conditions and Dissociation Enthalpies. J. Chem. Eng.
Data 2010;55:1271-1275.
[26] Shimada W, Ebinuma T, Oyama H, Kamata Y,
Takeya S, Uchida T, Nagao J, Narita H. Separation of
Gas Molecule Using Tetra-n- butylammonium Bromide
Semi-Clathrate Hydrate Crystals. Jpn. J. Appl. Phys.
2003;42:L129-L131.
[27] Kamata Y, Oyama H, Shimada W, Ebinuma T,
Takeya S, Uchida T, Nagao J, Narita H. Gas Separation
Method Using Tetra-n- butyl Ammonium Bromide
Semi-Clathrate Hydrate. Jpn. J. Appl. Phys.
2004;43:362-365.
[28] Li DL, Du JW, Fan SS, Liang DQ, Li XS, Huang
NS. Clathrate Dissociation Conditions for Methane +
Tetra-n-butyl Ammonium Bromide (TBAB) + Water. J.
Chem. Eng. Data 2007;52:1916-1918.
[29] Kamata Y, Yamakoshi Y, Ebinuma T, Oyama H,
Shimada W, Narita H. Hydrogen Sulfide Separation
Using Tetra-n-butyl Ammonium Bromide Semiclathrate
(TBAB) Hydrate. Energy & Fuels 2005;19:1717-1722.
[30] Ahmadloo F, Mali G, Chapoy A, Tohidi B. Gas
Separation and Storage Using Semi-Clathrate
Hydrates. In: Proceedings of 6th International
Conference on Gas Hydrates,Vancouver, 2008.
[31] Wang W, Carter BO, Bray CL, Steiner A, Bacsa J,
Jones JTA, Cropper C, Khimyak YZ, Adams DJ,
Cooper AI. Reversible Methane Storage in a Polymer-
Supported Semi-Clathrate Hydrate at Ambient
Temperature and Pressure. Chem. Mater.
2009;21:3810-3815.
[32] Su F., Bray CL, Tan B, Cooper AI. Rapid and
Reversible Hydrogen Storage in Clathrate Hydrates
Using Emulsion-Templated Polymers. Adv. Mater.
2008;20:2663-2666.
[33] Bogatyryov VL, Dyadin YuA, Pirozhkov AV,
Maksakova GA, Zemskova SM, Moroz NK, Zhurko
FV, Skobeleva VI, Villevald GV. Klatratnye
poligidraty polimerov (Clathrate polyhydrates of
polymers) Izv. Akad. Nauk SSSR, Ser. Khim. Nauk
1986;9:2152 (in Russian).
[34] Bruker AXS Inc. 2004: APEX2 (Version 1.08),
SAINT (Version 7.03), SADABS (Version 2.11),
Madison, Wisconsin, USA
[35] Manakov AYu, Dyadin YuA, Ogienko AG,
Kurnosov AV., Aladko EYa, Larionov EG, Zhurko FV,
Voronin VI, Berger IF, Goryainov SV, Likhacheva
AYu, Ancharov AI Phase diagram and high-pressure
boundary of hydrate formation in the carbon dioxide –
water system J.Phys.Chem.B 2009:113:7257-7262.
13
[36] Ogienko AG, Kurnosov AV, Manakov AYu,
Larionov EG, Ancharov AI, Sheromov MA, Nesterov
AN, High pressure gas hydrates. Composition, thermal
expansion and self-preservation. J.Phys.Chem.B
2006:110: 2840-2846.
[37] Dyadin YuA., Terekhova IS, Polyanskaya TM,
Aladko LS. Clathrate hydrates of tetrabutylammonium
fluoride and oxalate. J.Struct.Chem. 1977;17:566-572
(translated from Russian Zh.Struct.Khim.1976;17:655-
661).
[38] Narten AH, Lindenbaum S. Diffraction Pattern
and Structure of the System Tetra-n-butylammonium
Fluoride – Water at 25oC. J.Chem.Phys. 1969; 51(3):
1108-1114
[39] Nakayama H. Solid-Liquid and Liquid – Liquid
Phase Equilibria in the Symmetrical Tetraalkyl-
ammonium Halide-Water Systems. Bull. Chem. Soc.
Jpn. 1981; 54:3717-3722.
[40] Rodionova TV, Manakov AYu, Stenin YuG,
Villevald GV, Karpova TD. The heats of fusion of
tetrabutylammonium fluoride ionic clathrate hydrates.
J. Incl.Phenom.Macrocycl.Chem. 2008;6:107-111.
[41] Rodionova T, Komarov V, Villevald G, Aladko L,
Karpova T, Manakov A. Calorimetric and Structural
Studies of Tetrabutylammonium Chloride Ionic
Clathrate Hydrates. J. Phys. Chem. B. 2010;
114(36):11838–11846.
[42] Nakayama H. Hydrates of Organic Compounds.
VI. Heats of Fusion and of Solution of Quaternary
Ammonium Halide Clathrate Hydrates. Bull. Chem.
Soc. Jpn.1982; 55:389-393.
[43] Nakayama H. Hydrates of Organic Compounds.
XI. Determibation of the Melting Point and Hydration
Numbers of the Clathrate-Like Hydrate of
Tetrabuylammonium Chloride by Differential Scanning
Calorimetry. Bull. Chem. Soc. Jpn.1987;60:839-843
[44] Aladko LS, Dyadin YuA. Clathrate Formation in
the Bu4NCl−NH4Cl−H2O system. Mendeleev
Commun.1996;198-200.
[45] Dyadin YuA, Udachin KA. Clathrate Formation in
Water – Peralkylonium salts Systems. J. Incl. Phen.
1984;2:61-72.
[46] Lipkowski J, Komarov VYu, Rodionova TV,
Dyadin YuA, Aladko LS. The structure of
tetrabutylammonium bromide hydrate
(C4H9)4NBr.21/3H2O. J.Supram.Chem. 2002;2:435-
439.
[47] Shimada W, Shiro M, Kondo H, Takeya S, Oyama
H, Ebinuma T, Narita H. Tetra-n-butylammonium
bromide – water (1/38). Acta Crystallographica, C.
2005;C61:065-066.
[48] Terekhova IS, Bogatyryov VL, Dyadin YuA.
Clathrate Hydrates of Cross-Linked
Tetraisoamylammonium Polyacrylates. J. Supramol.
Chem. 2002;2:393-399.
[49] Terekhova IS, Manakov AYu, Feklistov VV,
Dyadin YuA, Komarov VYu, Naumov DYu. X-Ray
Powder Diffraction Studies of Polyhydrates of Cross-
Linked Tetraisoamylammonium Polyacrylates. J.
Inclusion Phenom. and Macrocyclic Chem.
2005;52:207-211.
[50] Soldatov DV, Suwinska K, Terekhova IS,
Manakov AYu. Structural Investigation of Hydrate
Compounds of Tetraisoamylammonium form of
Polyacrylate Ion Exchange Resins. J. Struct. Chem.
2008;49(4):712-718.
[51] Suwinska K, Lipkowski J, Dyadin YuA, Komarov
VYu, Terekhova IS, Rodionova TV, Manakov AYu.
Clathrate Formation in Water –
Tetraisoamylammonium Propionate System: X-ray
Structural Analysis of the Clathrate Hydrate (i-
C5H11)4NC2H5CO2·36H2O. J.Incl.Phen. 2006;56:331-
335.
[52] Feil D, Jeffrey GA. The Polyhedral Clathrate
Hydrates, Part 2. Structure of the Hydrate of Tetra Iso-
Amyl Ammonium Fluoride. J. Chem. Phys.
1961;35(5):1863-1873.
[53] Udachin KA, Ripmeester JA. A Polymer Guest
Transforms Clathrate Cages into Channels: The Single
Crystal X-Ray Structure of Tetra-n-Butylammonium
Polyacrylate Hydrate nBu4NPA*40H2O. Angew. Chem.
Int. Ed. 1999;38(13/14):1983-1984.
[54] Terekhova IS, Manakov AYu, Soldatov DV,
Suwinska K, Skiba SS, Stenin YuG, Villevald GV,
Karpova TD. The Calorimetric and X-ray Studies of
Clathrate Hydrates of Tetraisoamylammonium
Polyacrylates. J. Phys. Chem. B 2009;113(17):5760-
5768.
[55] Nakayama H. Hydrates of Organic Compounds.
XIII. The Conformation of the Formation of Clathrate -
Like Hydrates of Tetrabutylammonium and
Tetraisopentylammonium Polyacrylates. Bull. Chem.
Soc. Jpn. 1987;60:2319-2326.