Crystal structures of four inclusion compounds of 2,2′-dithiosalicylic acid and tetraalkylammonium

Article abstract of DOI:10.1080/15421406.2017.1415661

Herein four inclusion compounds of 2,2′-dithiosalicylic acid and tetraalkylammonium, 2(CH₃)₄N⁺·C₁₄H₈O₄S₂ ^2?·H₂O (1), (C₂H₅)₄N⁺·C₁₄H₉O₄S₂ ^?·0.25H₂O(2), (n-C₃H₇)₄N⁺·C₁₄H₉O₄S₂ ^? (3) and (n-C₄H₉)₄N⁺·C₁₄H₉O₄S₂ ^?(4) are prepared and characterized by X-ray single crystal diffraction. As shown in the results, compounds 1 and 3 belong to orthorhombic crystal system with different space groups of P2₁2₁2₁ and Pca2₁, and 2 and 4 are monoclinic system with similar groups of P2₁/n and P2₁/c. The crystallography data are displayed below: 1: a = 10.5903(7) ?, b = 10.6651(7) ?, c = 21.9476(13) ?, V = 2478.9(3) ?³, Z = 4, R₁ = 0.0359; 2: a = 8.13340(1) ?, b = 22.0741(3)?, c = 13.2143(2)?, β = 101.6360(1) °, V = 2323.70(6) ?³, Z = 1, R₁ = 0.0385; 3: a = 15.7857(2) ?, b = 8.24830(1) ?, c = 20.2599(2) ?, V = 2637.94(5) ?³, Z = 4, R₁ = 0.0308_degree4: a = 11.7476(2) ?, b = 17.1346(1) ?, c = 16.3583(3)?, β = 109.4560(1) °, V = 3104.74(9)?³, Z = 4, R₁ = 0.0562. Interestingly, although the carbon chains of the guest templates vary from methyl group to butyl group, the host molecules of 2,2′-dithiosalicylic acid all construct the similar 2D hydrogen-bonded host layers with or without the existence of water molecules to contain the guest templates to yield analogous sandwich-like inclusion compounds. Obviously, although the guest templates will have certain effects on the ultimate formation of these crystal structures, the host molecule of 2,2′-dithiosalicylic acid is a controlling factor to form these four inclusion compounds.

Full text of DOI:10.1080/15421406.2017.1415661

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Crystal structures of four inclusion compounds of
2,2′-dithiosalicylic acid and tetraalkylammonium
Yunxia Yang, Wenjing Dong, Lihua Li, Li Zhang, Jinfeng Wu, Haiyan Li & Bing
Yin
To cite this article: Yunxia Yang, Wenjing Dong, Lihua Li, Li Zhang, Jinfeng Wu, Haiyan
Li & Bing Yin (2017) Crystal structures of four inclusion compounds of 2,2′-dithiosalicylic
acid and tetraalkylammonium, Molecular Crystals and Liquid Crystals, 658:1, 165-176, DOI:
10.1080/15421406.2017.1415661
To link to this article: https://doi.org/10.1080/15421406.2017.1415661
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Crystal structures of four inclusion compounds of
,ꢀ-dithiosalicylic acid and tetraalkylammonium
Yunxia Yanga, Wenjing Donga, Lihua Lia, Li Zhanga, Jinfeng Wua, Haiyan Lia, and Bing Yinb
aKey Laboratory of Polymer Materials of Ministry of Education, College of Chemistry and Chemical Engineering,
Northwest Normal University, Lanzhou, Gansu, PR China; bMOE Key Laboratory of Synthetic and Natural
Functional Molecule Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry
and Materials Science, Northwest University, Xi’an, Shanxi, PR China
ABSTRACT
KEYWORDS
Crystal structure; hydrogen
bond; inclusion compounds
Herein four inclusion compounds of 2,2ꢀ-dithiosalicylic acid
and
tetraalkylammonium,
2(CH3)4N+·C14H8O4S22−·H2O
(1),
(C2H5)4N+·C14H9O4S2−·0.25H2O(2), (n-C3H7)4N+·C14H9O4S2
(3) and
−
(n-C4H9)4N+·C14H9O4S2−(4) are prepared and characterized by X-ray
single crystal diffraction. As shown in the results, compounds 1 and 3
belong to orthorhombic crystal system with different space groups
of P212121 and Pca21, and 2 and 4 are monoclinic system with similar
groups of P21/n and P21/c. The crystallography data are displayed below:
3
˚
˚
˚
˚
˚
1: a = 10.5903(7) A, b = 10.6651(7) A, c = 21.9476(13) A, V = 2478.9(3) A , Z
˚
˚
˚
= 4, R1 = 0.0359; 2: a = 8.13340(1) A, b = 22.0741(3)A, c = 13.2143(2)A, β =
3
˚
˚
101.6360(1) °, V = 2323.70(6) A , Z = 1, R1 = 0.0385; 3: a = 15.7857(2) A, b =
3
˚
˚
8.24830(1) A, c = 20.2599(2) A, V = 2637.94(5) A , Z = 4, R1 = 0.0308degree4:
˚
˚
˚
a = 11.7476(2) A, b = 17.1346(1) A, c = 16.3583(3)A, β = 109.4560(1) °, V
3
˚
= 3104.74(9)A , Z = 4, R1 = 0.0562. Interestingly, although the carbon
chains of the guest templates vary from methyl group to butyl group,
the host molecules of 2,2ꢀ-dithiosalicylic acid all construct the similar
2D hydrogen-bonded host layers with or without the existence of
water molecules to contain the guest templates to yield analogous
sandwich-like inclusion compounds. Obviously, although the guest
templates will have certain effects on the ultimate formation of these
crystal structures, the host molecule of 2,2ꢀ-dithiosalicylic acid is a
controlling factor to form these four inclusion compounds.
Introduction
One of the most important problems of crystal engineering is crystal structure prediction
(CSP) [1]. It’s a tough task to predict the crystal structure from the original organic molecule
due to many reasons such as temperature, solvent, pH value, molecular configuration, weak
interaction and so on. Thus, if some variables can be fixed during the formation of the crystals
and only one or two variables are adjusted, it is very possible to obtain beneficial results to
provide useful information for CSP.
In our systematic research of crystal structures of inclusion compounds, one host
molecule with special configuration was often adopted to interact with the guest
CONTACT Yunxai Yang
yangyx@.com
University, Anning District of Lanzhou, Gansu , China.
College of Chemistry and Chemical Engineering, Northwest Normal
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

166
Y. YANG ET AL.
template of tetraalkylammonium to understand various weak interactions in the host-
guest system and the infection of varied carbon chains of the guest templates [2]. And
2,2ꢀ-dithiosalicylic acid (DTSA) came into our eyes because it can generate hydrogen bonds
with its COOH groups and it also can freely rotate with its S-S bond to get a relatively
flexible configuration. As a multi-carboxyl multi-ring aromatic host molecule with ‘L’
configuration, DTSA is usually applied as the ligand of different MOFs [3] and its metal
derivatives have special medicinal values [4]. As we know, the crystal structure of DTSA
has been reported before [5] and it shows DTSA indeed displays good ability to form
hydrogen bonds with its functional groups. At the same time, the two central S atoms, to
some degree, make the two terminal rigid benzene rings rotate with each other to obtain
abundant hydrogen-bonded linking modes and various packing patterns. Searching in CSD
database [6], DTSA can interact with many compounds, such as methyltriethylammonium
chloride [7], pyridine [8], hexamethylenetetramine [9], isoniazid [10], 1,4,10,14-tetraoxa-
7,16-dizazcyclo-octadecane [11], bipyridine [12], bipyridine derivatives [13], tetrahydrofuran
[14], 1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-aminium [15], aminopyri-
dine [16], 1,1ꢀ-(p-phenylenedimethylidene)diimidazol-3-ium [17], sulfanylbenzoic acid [18],
azanium [19] and iminodiethanaminium [20], to yield a plenty of interesting cocrystals, in
which the molecules of DTSA emerge as the ‘L’ configuration along the central S-S axis with
the interplanar angles between two terminal benzene rings being near to 90° and the S←O
hypervalent bonds existed between S atoms and the neighboring O atoms also consolidate
the special shape of DTSA molecules [13]. Therefore, DTSA can be thought of as a potential
host molecule that is a rigid aromatic molecule with relative flexibility.
Herein, DTSA was adopted as the host molecule to react with four tetraalky-
lammonium hydroxides with varied carbon chains to get four inclusion compounds
with the same solvents of H2O/EtOH (v:v = 2:1): 2(CH3)4N+·C14H8O4S22−·H2O
−
(1), (C2H5)4N+·C14H9O4S2−·0.25H2O (2), (n-C3H7)4N+·C14H9O4S2
(3) and (n-
−
C4H9)4N+·C14H9O4S2 (4). Analyzing these crystal structures, in compound 1, DTSA2−
anion links the only water molecule with O-H …O interactions to yield the 2D waving host
layers to contain two tetramethylammonium cations to form the sandwich-like structure,
and DTSA− anions of compounds 2–4 generate long hydrogen-bonded chains by themselves
with O-H …O contacts to yield the layer host lattices, in which different guest cations are
accommodated between the layers to construct the ultimate crystal structures. Interestingly,
although different guest cations with varied carbon chains were used in the experiments,
the final crystal packing modes all show similar layer host lattices and sandwich-like
structures. From here, we can see that the host molecule of DTSA is a more significant
factor to control the final crystal structures during the formation of these four inclusion
compounds.
Experimental
Synthesis of inclusion compounds
DTSA (98%, A. R.) was purchased from Alfa Company and tetraalkylammonium hydrox-
ides (25% aqueous solution, A. R.) were from Aladdin company. DTSA and the correspond-
ing tetraalkylammonium hydroxides were dissolved in small quantities of water/ethanol
(100/50 v/v) with a 1: 2 molar ratio. The mixtures were stirred for about half an hour and
set aside to crystallize, finally yielding yellow block crystals suitable for single crystal X-ray
diffraction after 15 days.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
167
X-ray data collection and structure determination
Crystals of four compounds were mounted on glass fibers for geometry and intensity data
collection with a Bruker SMART Apex II CCD area detector [21] at room temperatures. The
structures were solved with the direct methods and refined by full matrix least square meth-
ods based on F2, using the structure determination and graphics package SHELXTL [22]. All
non-hydrogen atoms were refined with anisotropic displacement parameters, and all H atoms
bonded to C atoms were introduced in idealized dispositions. The H atoms bonded to O atoms
were located in the difference maps and refined with the riding model with the fixed distance
˚
of 0.86 A. The crystallography information was tabulated in Table 1 and selected bond lengths
and angles were in Table 2.
Results and discussion
Crystal structure description
Crystal structure of  (CH)N+·CHOS−·HO
Compound 1 belongs to orthorhombic system, in which there are one DTSA2− anion, two
tetramethylammonium cations and one independent water molecule in its asymmetric unit.
Observing the configuration of DTSA2− anion, the interplanar angle between two terminal
benzene rings that are coplanar (the mean deviation values from the least-square planes are
˚
˚
0.0060 A and 0.0104 A) is 76.5° and the related dihedral angles between two deprotonated
carboxyl groups and the neighboring rings are 43.6° and 25.1° separately. Obviously, two car-
boxyl groups retort to some degree, which is inconsistent with the normal planar conjugate
structure of benzoate, and it can be concluded that the interactions between water molecule
and DTSA2− anion result in the distortion mentioned above to adapt the needs during the
˚
crystal packing. Additionally, S←O hypervalent bonds of the host anion are 2.835 A and
˚
2.634 A, in which the weaker one can be attributed to the carboxyl group that has a smaller
retorting angle and the stronger one is the carboxyl group of greater torsion angle.
Due to the total deprotonation, DTSA2− anion can just act as the proton donor to inter-
act with some proton acceptor such as water molecule. From the hydrogen-bonded linking
diagram of compound 1 (Fig. 1b), DTSA2− anion connects with water molecule by O-H …O
hydrogen bonds to generate the long waving anionic chain along the b axis and two neighbor-
ing 21-related chains fit each other to yield undulating double hydrogen-bonded layers that
are repeatedly assigned along the a axis, then two guest cations are orderly accommodated
between the double layers to form the stable sandwich-like structure as shown in Fig. 1a.
Clearly, water molecule is a very important linking unit in this structure. It is these two
O-H …O hydrogen bonds of water and DTSA2− anion that lead to the formation of the long
anionic chain which is the elementary unit of forming the host layers of compound 1.
Crystal structure of  (CH)N+·COHS−·.HO
Compound 2 crystallizes in monoclinic system. Its asymmetric unit contain one independent
DTSA− ion, one tetraethylammonium ion and one position-disordered water molecule with
the occupancy of 0.25. Compared with compound 1, the dihedral angle of two benzene rings
˚
˚
(the mean deviation values of the rings are 0.0024 A and 0.0094 A) is also 76.5°, but the torsion
angles of two carboxyl groups related to their rings are very different with the corresponding
values of 3.7° and 3.6°. That is to say, two carboxyl groups of the host anion in this compound
are almost coplanar with the abut rings. By calculation, S←O distance existing between S

168
Y. YANG ET AL.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
169
˚
Table . Selected bond lengths (A) and bong angles (°).
Compound 1
S()-C()
.()
.()
.()
S()-S()
C()-C()
O()-C()
.()
.()
.()
O()-C()
O()-C()
O()-C()
.()
C()-C()
.()
.()
.()
.()
.()
.()
C()-S()-S()
C()-C()-S()
C()-N()-C()
C()-N()-C()
O()-C()-O()
C()-N()-C()
C()-N()-C()
Compound 2
S()-C()
O()-C()
O()-C()
O()-C()
C()-C()
.()
.()
.()
.()
.()
.()
.()
C()-C()-S()
C()-N()-C()
C()-N()-C()
C()-S()-S()
C()-N()-C()
C()-N()-C()
.()
.()
.()
.()
.()
.()
S()-S()
C()-S()
O()-C()
C()-C()
C()-S()
.()
.()
.()
.()
.()
C()-C()
.()
C()-S()-S()
O()-C()-C()
O()-C()-O()
C()-N()-C()
C()-N()-C()
Compound 3
S()-C()
S()-S()
O()-C()
O()-C()
.()
.()
.()
.()
.()
O()-C()-C()
C()-C()-S()
O()-C()-O()
C()-N()-C()
C()-N()-C()
.()
.()
.()
.()
.()
.()
.()
.()
S()-C()
O()-C()
O()-C()
C()-C()
.()
.()
.()
.()
.()
C()-C()
.()
C()-N()-C()
C()-N()-C()
C()-C()-S()
C()-C()-S()
O()-C()-O()
C()-C()-C()
C()-C()-C()
Compound 4
N()-C()
N()-C()
N()-C()
N()-C()
O()-C()
C()-N()-C()
C()-N()-C()
C()-S()-S()
C()-C()-S()
C()-S()-S()
O()-C()-C()
O()-C()-C()
.()
.()
.()
.()
.()
.()
.()
C()-N()-C()
C()-N()-C()
C()-S()-S()
.()
.()
.()
.()
.()
.()
.()
C()-S()-S()
O()-C()-O()
C()-C()-C()
C()-C()-C()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
S()-C()
S()-S()
S()-C()
O()-C()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
O()-C()
C()-N()-C()
C()-N()-C()
C()-C()-S()
O()-C()-O()
O()-C()-O()
O()-C()-C()
O()-C()-C()
.()
˚
atom and the carbonyl O atom of the COOH group is 2.680 A, while another S←O of the
−
˚
deprotonated COO group is just 2.611A. From this, it can be judged that the torsion angle
of the related carboxyl group is not the only affecting factor to S←O hypervalent bond. It
can be imagined that the electron atmosphere of S and O atoms would interact with each
other to form S←O hypervalent bond. To the deprotonated carboxyl group, its carbonyl O
atom should bear dense electron cloud, which may facilitate to get stronger S←O hypervalent
bond. Thus, it can be explained why S atom and the neighboring carbonyl O atom of the
COO− group can produce stronger S←O interaction even though the torsion angles of two
carboxyl groups are so approximate.

170
Y. YANG ET AL.
Figure . (a) The packing diagram of compound 1 (for clarity, tetramethylammonium cations were repre-
sented with the big shaded spheres). (b) The projection diagram of the double hydrogen-bonded layer
along the c axis in compound 1 (all H atoms bonded to C were omitted for simplicity) [A: x,  + y, z;
B:  – x, / + y,  – z].
It can be easily seen that DTSA− anion utilizes the only independent O-H …O con-
tact to obtain the corresponding long anionic chain along the b axis (Fig. 2b), and the
adjacent 21-related chains are orderly arranged along the c axis, which is very similar
with the linking mode of compound 1. Comparatively, DTSA− anion can just be mis-
placed with each other to yield Z-type hydrogen-bonded layer in compound 2 because
the host anion has greater steric effects for the absence of water molecule and cannot
fit each other to produce the packing mode just as compound 1. Ultimately, in com-
pound 2, the greater tetraethylammonium ion and the guest water molecule are col-
lectively contained between the Z-type layers to get the sandwich-like crystal structure
(Fig. 2a).
−
Crystal structure of  (n-CH)N+·CHOS
Similar with compound 1, compound 3 also belongs to orthorhombic system with the extra
sliding planes. In the asymmetric unit, the content is similar with compound 2 except the

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
171
Figure . (a) The packing diagram of compound 2 (for clarity, all H atoms bonded to C atoms and O atoms
of water molecules are omitted and the guest cations are represented with big shaded spheres). (b) The
hydrogen-bonded linking mode of DTSA− anion along the a axis (all H atoms bonded to C are omitted for
clarity) [A: / – x, -/ + y, / – z; B: / – x, / + y, / – z; C:  – x,  – y,  – z; D: -/ + x, / – y, / + z;
E: -/ + x, / – y, / + z].
water molecule. The packing pattern of compound 3 is also approximate to compound 2, in
which the anionic chains of DTSA− anion extending along the c axis are repeatedly placed to
generate the 2D host layers to contain the guest tetrapropylammonium to construct the final
structure (Fig. 3).
Comparatively, two benzene rings of DTSA− anion deviate their least-square planes
˚
˚
with the related values of 0.0045 A and 0.0061 A and the interplanar angle is 81.2°.
Unexpectedly, S←O interaction between S and O derived from COO− group that has
˚
a torsion angle of 6.1° is 2.680 A and another S←O involving COOH group (the
˚
related torsion angle is 12.1°) is 2.677 A, which is not accordant with our estimation
of the former should bear stronger hypervalent bond and it may be attributed to the

172
Y. YANG ET AL.
Figure . (a) The packing diagram of compound 3 (for clarity, all H atoms bonded to C are omitted and the
guest ions are represented with big shaded spheres). (b) The projection diagram of the hydrogen-bonded
patternalongtheaaxisincompound3(forsimplicity, allHatomsbondedtoCareeliminatedandthepurple
line represents C-H …π interaction) [A:  – x,  – y, / + z; B: x,  + y, z].
greater retorting angle between two terminal benzene rings compared with compounds
1 and 2.
−
Crystal structure of  (n-CH)N+·CHOS
Compound 4 has the same crystal system as compound 2 and the content of the asymmetric
unit is approximate to that of 3, and the hydrogen-bonded pattern and the packing mode of
4 is also similar with compound 3 (Fig. 4). Calculating the parameters of the host DTSA−
anion, the dihedral angle between two rings is 87.1°, in which the−related deviation values of
˚
˚
the rings are 0.0090 A and 0.0061 A. The distortion angle of COO group is just 0.6° and the
˚
related S1←O2 bond distance is 2.547 A, and another torsion angle of COOH is 8.1° and the
−
˚
corresponding S2←O3 is 2.682 A. It is explicit that the COO group with smaller torsion
angle takes part in the construction of the stronger S←O hypervalent bond in compound 4.
Disccusion
Compounds1–4 are prepared with DTSA and different tetraalkylammonium hydroxides with
the same molar ratio of 1:2 under room temperature. By analyzing the crystallography results,
it can be seen that compounds 1 and 3 belong to orthorhombic system with high symmetry

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
173
Figure . (a) The packing diagram of compound 4 (for clarity, all H atoms bonded to C are omitted and tetra-
butylammonium is represented with the big shaded circle). (b) The projection diagram of the hydrogen-
bonded pattern along the b axis in compound 4 (for simplicity, all H atoms bonded to C are eliminated
and the purple line represents C-H …π interaction) [A: /+x,/−y,−/−z; B: −/+x,/−y,/+z; C:
/+x,/−y,/+z].
and 2 and 4 are monoclinic system. Noticeably, S←O hypervalent bond is a three-center four-
electron bond to effectively stabilize the configuration of DTSA. As reported in the literatures,
˚
˚
the distance of S←O varies from 2.561A to 2.787A [6], and the related values in the title com-
˚
˚
˚
˚
pounds are 2.547 A∼2.835 A. In compound 1, S←O bonds are 2.634 A and 2.835A, and the
stronger bond belongs to the COO− group with a smaller torsion angle of 25.1°; in com-
˚
˚
pound 2, S←O distances are 2.680 A and 2.611 A, in which two torsion angles of the related
carboxyl groups are very approximate to 4° and the interplanar angle between two rings is the
same as that in compound 1, and the stronger S←O is also generated by the COO− group; in
˚
˚
compound 4, S←O values are 2.547A and 2.682A, and the stronger S←O also exists in the
COO− group with smaller torsion angle of 0.6°. Only in compound 3, the hypervalent bonds
of S←O don’t display the same tendency as in compounds 1, 2 and 4. The related distances are
˚
˚
2.677 A and 2.680 A, which may be attributed to the larger interplanar angle of two rings and
the larger torsion angles of two carboxyl groups. However, in the cases of DTSA, the hyperva-
lent bond generated between S atom and the deprotonated carboxyl group should be stronger
and if two protons are both eliminated, the torsion angle between the carboxyl group and the
neighboring ring should be another crucial factor to affect the S←O interaction. Analyzing
the corresponding data of 38 organic crystals of DTSA found in CSD database [6], between

174
Y. YANG ET AL.
Figure . After optimization of the DTSA− anion structure.
Table . WBI, OWBO and NLMO are three different bond orders.
˚
Distance(A)
WBI
OWBO
NLMO
SꢀO
SꢀO
.
.
.
.
.
.
.
.
−
˚
S atoms and the neighboring COO groups, the shortest distance is 2.561 A and the related
˚
torsion angle is 3.7° and the longest one is 2.787 A and the angle is 33.5°; between S atoms and
the adjacent COOH groups, the shortest value is 2.567 A and the torsion angle is 4.3° and the
longest one is 2.759 A and the angle is 21°. From this, we can see that, due to complicated inter-
˚
˚
actions among the crystals, the weakest S←O contact occurs in COO− group unexpectedly,
but from the data mentioned above, we also can conclude that if the COO− group in DTSA
anion has a smaller torsion angle, then the related S←O interaction should be stronger under
normal conditions. Interestingly, analysising structure of four crystals shows that the config-
uration of the host molecules are very similar, we found that C14H10O4S2 stably exist with
special structure, and a certain interaction between the carboxyl oxygen and sulfur atoms
in the same benzene ring connected in a certain condition meta-position. As an example,
we optimize the molecular structure of compound 1 (Fig 5.). The molecule was optimized
using BP86 method, SVP basis set, and compute the key stage (Table 3: WBI, OWBO and
NLMO are three different key level) and orbit interaction (Table 4: LP-lone pair orbital, BD∗-
anti-bonding orbital, SOIE-second-order orbital interaction energy) of S1 …O3 and S4 …O9.
There are three key stage results show that S1 …O3 and S4 …O9 becoming the weak force,
respectively. The results of the analysis showed that, O3 or O9 lone electron pair have the inter-
action between anti-bonding orbital of S1 and S4, this result show that S1 …O3 and S4 …O9
becoming the weak force, too. Whether it is from the key level or orbit interaction, it has an
effect between O and S.
Compared with other similar V-shaped molecules that have two terminal hydroxyl groups
(or carboxyl groups), the S-S bond in DTSA can rotate more flexibly to adjust its molecular
configuration to meet different needs. And DTSA also can easily lose its protons to generate
Table . LP-lone pair orbital, BD∗-anti-bonding orbital, SOIE-second-order orbital interaction energy.
donor/acceptor
SOIE (K cal/mol)
LP(O)/BD∗(S-S)
LP(O)/BD∗(S-S)
.
.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
175
Table . Hydrogen-bonding geometry.
O …O
distance (A)
O …O
distance (A)
˚
˚
Hydrogen bonds
Hydrogen bonds
Compound 1
OW -H …OA
C -H …OC
C- H …OE
C -H …OF
C -H …OE
.
.
.
.
.
OW -H …O
C -H …OD
C-H …O
.
.
.
.
C -H …OWG
C: /+x, /−y, −z; D: /+x, /−y, −z; E: x, −+y, z; F: +x, y, z; G: +x, y, z
Compound 2
O -H …OA
Compound 3
OA -H …O
C -H …OC
C -H …OD
.()
C -H …OD
.()
.
.
.
C -H …OC
C-H …OE
.
.
C: x, −+y, z; D: −x, −y, /+z; E: −x, −y, −/+z
Compound 4
O-H …OB
.
.
C-H …OD
C-H …OE
.
.
C-H …OC
D: /−x, −/+y, /−z; E: +x, y, z
different anions under basic conditions. As shown here, DTSA− tends to yield the hydrogen-
bonded chain and DTSA2− needs some hydrogen bond donor (such as water molecule) to
participate the construction of the host layer. Obviously, both of the anions display similar
linear configuration, which have the tendency of forming 1D hydrogen-bonded chains that
can be orderly assigned to obtain 2D host layers without the existence of other ancillary host
molecules. It can be imagined that various crystal structures with different packing patterns
can be obtained if other auxiliary host molecules that can form varied hydrogen bonds can
take part in the formation of the host layers.
In addition, it can be calculated with PLATON [23] that the crystal packing coefficients
of compounds 1–4 are 0.681, 0.656, 0.673 and 0.647 sequentially, which means the packing
coefficients decrease when the volumes of the guest tetraalkylammonium cations increase.
Clearly, guest molecules have concrete affection on the intensity packing of host-guest inclu-
sion compounds. Among the four title compounds, the unique coefficient of compound 2 may
be attributed to the occupation of the water molecule that is also regarded as a guest molecule
here.
Conclusion
In conclusion, four tetraalkylammonium inclusion compounds with the host molecule of
DTSA were synthesized and characterized by single X-ray single crystal diffraction. As shown
in the results, the host DTSA anions of compounds 1–4 all generate long similar hydrogen-
bonded chains that will produce approximate 2D host layers to accommodate the related
guest cations with varied magnitudes to finally form sandwich-like crystal structures. Also,
the packing coefficients of 1, 3 and 4 are decreasing with the increasing of the volumes of the
related guest molecules, which show the definite effects of the guest molecules in host-guest
system. Interestingly, although the carbon chains of the guest templates are different, the final
packing modes of the crystal structures are very approximate, which means the host molecule
of DTSA is a more important factor during the crystal packing. Additionally, in these four
structures, there always exist weak C-H …O hydrogen bonds between the guest ions and the

176
Y. YANG ET AL.
host layers, which enforce the interdependence of host-guest system to form the final stable
inclusion compounds.
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