Comparison of non-covalent interactions and spectral properties in 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium mono- and tetraiodide crystals

Article abstract of DOI:10.1007/s11224-019-01372-3

The reaction of 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium (MTPT) iodide with diiodine in a solution leads to monoiodide crystal structure that in excess of iodine gives the unusual tetraiodide anion with two central iodine atoms in disorder. The bonding within the anion has been characterized as I^–…I₂…I^–; the existence of the bound iodine molecule inside has been proven by the characteristic band in experimental and calculated Raman spectra. Non-covalent interactions of MTPT in considered crystal structures are different. Monoiodide anion as a strong electron donor allows the formation of the S…I chalcogen bonds that are absent in tetraiodide structure. The features of halogen bonds within the I₄ ^2– anion are?also performed.

Full text of DOI:10.1007/s11224-019-01372-3

Structural Chemistry
https://doi.org/10.1007/s11224-019-01372-3
ORIGINAL RESEARCH
Comparison of non-covalent interactions and spectral properties
in 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium mono-
and tetraiodide crystals
1
1
1,2,3
1
Irina D. Yushina & Boris V. Rudakov & Adam I. Stash
& Ekaterina V. Bartashevich
Received: 12 April 2019 /Accepted: 3 June 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The reaction of 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium (MTPT) iodide with diiodine in a solution leads to
monoiodide crystal structure that in excess of iodine gives the unusual tetraiodide anion with two central iodine atoms
–
–
in disorder. The bonding within the anion has been characterized as I …I …I ; the existence of the bound iodine molecule
2
inside has been proven by the characteristic band in experimental and calculated Raman spectra. Non-covalent interactions
of MTPT in considered crystal structures are different. Monoiodide anion as a strong electron donor allows the formation
2
–
of the S…I chalcogen bonds that are absent in tetraiodide structure. The features of halogen bonds within the I4 anion
are also performed.
.
.
.
.
Keywords 1,2,4-Triazine 1,2,4-Triaziniumoligoiodide Tetraiodide Halogen bond Chalcogen bond
Introduction
and estrogen receptor modulators [7], so, for a long time, they
have attracted the attention of researchers. The anticonvulsant
6-(2,3-dichlorophenyl)-1,2,4-triazine-3,5-diamine (known by
the trade name “Lamotrigine”) is used in the treatment of bipolar
disorder [8, 9].
The sulfur-containing derivatives of 1,2,4-triazines, in ad-
dition to this, are the important classes of organic compounds
which exhibit a wide range of biological activities. For exam-
ple, the thio-indolotriazine derivative is used as a fungicide,
5,6-diphenyle-1,2,4-triazine possessing the thiosemicarbazide
moiety is a bactericidal agent, and 3-thio-5-cyclohexenyl-6-
oxo-1,2,4-triazine is a pesticide. Herbicidal activity is shown
by 4-amino-6-tert-butyl-3-methylsulfanyl-1,2,4-triazin-
The N-alkyltriazinium iodides are an attractive object of theoret-
ical and practical interest since both the cationic and anionic
components of these substances possess a number of various
unusual and beneficial properties. On the one hand,
heteroaromatic compounds with the 1,2,4-triazine moiety pos-
sess a wide spectrum of biological activities such as antifungal
[1], anticancer [2], analgesic and antihypertensive [3], antimalar-
ial [4], antiparasitic [5], and anti-inflammatory [6] activities; they
are also known as potential blood platelet aggregation inhibitors
Electronic supplementary material The online version of this article
5
(4H)-one, sold under the trade names “Sencor” or
(https://doi.org/10.1007/s11224-019-01372-3) contains supplementary
material, which is available to authorized users.
“Metribuzin,” widely used herbicide [7]. 5,6-Diphenyl-1,2,4-
triazine-3-thiol is one of the triazine derivatives that possess
anti-inflammatory activity [10].
*
Ekaterina V. Bartashevich
bartashevichev@susu.ru
Quaternary triazinium salts possess high reactivity, are attrac-
tive for researchers, and exhibit a series of transformations that
are unusual for N-alkylazinium salts. For example, 1-ethyl-3-
alkylthio-5-phenyl-1,2,4-triazinium under the action of
triethylamine forms 4a,4b,9,10-tetrahydro-1,3,6,8,8a,10a-
hexaazaphenanthrenes [11]. The derivatives of 1-alkyl-5-phe-
nyl-1,2,4-triazinium iodides have been found to undergo oxida-
tive dequaternization reaction easily, on treatment with
1
2
3
South Ural State University, Lenin Pr., 76, Chelyabinsk, Russia
4
54080
L.Ya. Karpov Institute of Physical Chemistry, Vorontsovo Pole 10,
Moscow, Russia 105064
A. N. Nesmeyanov Institute of Organoelement Compounds of
Russian Academy of Science, Vavilov st., 28, Moscow, Russia
119991

Struct Chem
triethylamine in alcohol or acetone solutions at room temperature
12], while other N-alkylazinium salts require significantly more
severe conditions.
tetraiodide anion I42−. The similar type of polyiodide anion
organization was previously described in the series of works
[
−
[27–31]. Tetraiodides can be either symmetric with equal I …
On the other hand, the area of practical use of the com-
pounds containing molecular iodine is rather large [13]. The
iodine-saturated compounds composed of an organic cation
and a polyiodide anion can be used as iodophors for water
disinfection [14]. It is important for the search for efficient
and safe bacteriostatic [15] and X-ray contrast compounds
I distances or asymmetric with non-equivalent distances.
2
−
−
Such structures are intermediate on the way to the I …I type
3
of tetraiodide; such reversible phase transition has been previ-
ously observed in the solid state under cooling for
dipirazolium salt and has been thoroughly discussed in the
work [28]. From the theoretic standpoint, the authors of the
paper [26] identify the following factors controlling asymme-
try of the tetraiodide anion: the crystal surrounding, especially
the localization and the value of positive charges nearby and
the possibility of electron delocalization.
[16]. The contemporary practical tasks stimulate permanent
interest in studies of the structural and physicochemical prop-
erties of new iodine-containing compounds [17].
Some of organic polyiodide compounds are able to exhibit
the conductive [18] and nonlinear optical properties [19].
Such crystals usually contain several polyiodide units, such
as tri- and oligoiodide anions. The diversity of their structural
disposition provides a great variety of polyiodide structures in
the solid state [20]. Polyiodides with organic cations contain-
ing sulfur atoms attract particular interest: they are known as
effective templates for self-assembly of polyiodide networks.
In addition, due to multiple S…I interactions [21] they are
promising for drug design [22] and low-temperature conduc-
Materials and Methods
Synthesis and crystallization
3-Methylthio-5-phenyl-1,2,4-triazine
3-Methylthio-5-phenyl-1,2,4-triazine 1 was synthesized in
two steps from thiosemicarbazide and phenylglyoxal hydrate
via S-methylthiosemicarbazide hydroiodide (Scheme 1).
Stage A. Thiosemicarbazide (4.55 g, 50 mmol) was heated
with methyl iodide (8.52 g, 60 mmol) at reflux in ethanol
(30 mL) for 8 h. The reaction mixture was cooled and the
precipitate was filtered off and dried in air, yielding 10.28 g
–
tors [23]. The unusual charge-assisted I …I halogen bonds are
observed between the asymmetric triiodide and diiodine units,
which include at least two diiodine fragments in some
oligoiodides [24–26].
In our research, we managed to synthesize the product of
N-alkyl-derived 1,2,4-triazinium salt and the rather rare
Scheme 1 Synthesis of 1-
Methyl-3-methylthio-5-phenyl-
1
,2,4-triazinium iodides

Struct Chem
(
88 %) of crude S-methylthiosemicarbazide hydroiodide.
determination, refinements, graphics, and structure reporting.
The structures were solved by direct methods and refined by
the full-matrix least-squares technique against F with the an-
Stage B. The crude S-methylthiosemicarbazide hydroiodide
obtained in stage A (6.44 g, 27.6 mmol) and 4.20 g (27.6
mmol) of phenylglyoxal hydrate were dissolved under mod-
erate heating in 30 mL of water, then 2.52 g (27.6 mmol) of
sodium bicarbonate was added to the resulting solution with
stirring.
The obtained precipitate was filtered off and recrystallized
from ethanol to yield 4.92 g (88 %) of 1 as yellow solid with
m.p. 98-99 C. H NMR in CDC1 : 2.67 (3H, s, methylthio
2
isotropic thermal parameters for all non-hydrogen atoms. The
hydrogen atoms were placed in the geometrically calculated
positions and included in the structure factors calculation in
the riding motion approximation, with the 0.98 Å length for
methylene H atoms with U (H) = 1.5U (C) and 0.95 Å
iso
eq
otherwise, and with U (H) = 1.2U (C). Crystal data, data
iso
eq
o
1
collection and structure refinement details are summarized in
Table 1; CCDC 1909732 and 1909733 contain supplementary
crystallographic data for 2 and 3, correspondently, which can
be obtained free of charge from The Cambridge
Crystallographic Data Centre.
3
groups), 9.32 (1H, s, H-6), 7.53, 8.1 ppm (5H, m, phenyl
groups).
1
-Methyl-3-methylthio-5-phenyl-1,2,4-triazinium iodide
Methyliodide (1.06 g, 7.5 mmol) was added to a suspension of
1.01 g, 5.0 mmol) 3-methylthio-5-phenyl-1,2,4-triazine 1 in
0 mL of ethanol and the reaction mixture was heated at reflux
Spectral experiment
(
2
Raman spectra were recorded with a NT-MDT NTEGRA
Spectra spectrometer using 632.8 nm line of a He-Ne laser
for 15 h. The obtained precipitate was filtered off and recrys-
+
tallized from ethanol to yield 1.2 g (69 %) of 2 as dark red
for spectra excitation. The laser power on the sample surface
was about 0.2 μW or less. We had to take into consideration
that the laser power had to be thoroughly controlled in order to
avoid decomposition under laser exposition, due to decreasing
thermal stability of higher polyiodides.
o
1
prisms with m.p. 185-188 C. H NMR in CD OD: 2.70 (3H,
3
s, methylthio group), 4.80 (3H, s, N-methyl group), 10.25
(
1H, s, H-6), 7.4-7.8, 8.10-8.35 ppm (5H, m, phenyl
group).To obtain the crystals, 0.05 g of 1-methyl-3-
methylthio-5-phenyl-1,2,4-triazinium iodide was dissolved
in 3 mL of acetonitrile. The resulting solution was placed in
a test tube of 15 mm diameter, which was closed with a stop-
per with a 3 mm hole, allowing the solvent to evaporate freely
at room temperature. Two weeks later dark red prisms were
formed. The structure 2 was determined by X-ray analysis.
Theoretical calculations
Periodical boundary conditions methodology implemented in
CRYSTAL17 program [34] was fulfilled during the atom po-
sition optimization with fixed cell parameters for crystal struc-
tures 2 and 3 using the hybrid B3LYP exchange-correlation
functional, TZVP basis set for C, H, N, S atoms [35] and
DZVP for I atoms [36]. K-point sampling was done using a
Monkhorst-Pack grid of 8 × 8 × 8. All optimized structures did
not detect negative modes in the Hessian matrix and thus
could be attributed to energy minimum and equilibrium state.
The calculated Raman spectra were obtained using couple-
perturbed Kohn-Sham procedure as implemented in
CRYSTAL17 [37]. Calculations of the electron density distri-
butions, eigenvalues of electron density Hessian matrix, po-
tential and kinetic energy densities, and the electron localiza-
tion function (ELF) [38] were performed using TOPOND14
1-Methyl-3-methylthio-5-phenyl-1,2,4-triazinium polyiodide
Iodide of 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium
MTPT) 2 (0.172 g, 0.5 mmol) was dissolved under moderate
(
heating in 5 mL of ethanol and mixed with iodine (0.127 g, 0.5
mmol), then the reaction mixture was heated at reflux for 5 h
and left overnight at room temperature. The obtained precip-
itate was filtered off and recrystallized from ethanol with the
yield 0.274 g (91.63 %) of MTPT polyiodide 3 as dark red
needles of good diffraction quality.
X-ray diffraction study
[39].
Single-crystal X-ray diffraction experiments were carried out
with a Bruker SMART APEX DUO diffractometer equipped
with an Oxford cryosystem Cobra (graphite monochromated
Mo-Kα radiation, λ = 0.71073 Å, ω-scan technique, T = 120
K). The APEX II software [32] was used for collecting frames
of data, indexing reflections, determination of lattice con-
stants, integration of intensities of reflections, scaling and ab-
sorption correction while the SHELXTL program package
Discussion
Crystal structure and description of non-covalent
interactions
Non-covalent interactions and crystal packing of MTPT with
[
33] was applied for the space group and structure
iodine moieties in monoiodide 2 and triiodide 3 differ: in 2 the

Struct Chem
Table 1 Crystallographic data
and experimental details for the
structure of compounds 2 and 3
Compound
2
3
Crystal data
Chemical formula
C H
11 12
N
3
S, I
11 12 3 2
C H N S, I, 0.5·I
Molecular weight
345.20
880.09
Crystal system, space group
Triclinic, P-1
120(2)
1
Monoclinic, P2 /n
Temperature (K)
a (Å)
10.2809(4)
10.7753(4)
13.5905(5)
68.010(1)
69.096(1)
77.617(1)
1298.44(9)
4
10.2363(4)
7.0620(3)
20.9001(9)
90
b (Å)
c (Å)
α (°)
β (°)
102.8811(8)
90
γ (°)
3
V (Å )
1472.82(11)
4
Z
Radiation type
α
Mo-K , λ = 0.71073 Å
-
1
μ (mm )
2.600
4.396
Crystal size (mm)
0.439 × 0.378 ×
.344
0.486 × 0.102 ×
0.080
0
Data collection
Diffractometer
Bruker SMART APEX II
Numerical (SADABS-2014/5. Bruker, 2013)
Absorption correction
Tmin, Tmax
0.448, 0.586
0.188, 0.778
No. of measured, independent and observed [I > 2σ(I)]
25,981, 9591, 8931
28,618, 5591, 4619
reflections
R
int
0.0157
0.781
0.0289
0.781
−1
(sinθ/λ)max (Å )
Refinement
2
2
2
R[F > 2σ(F )], wR(F ), S
0.0179, 0.0412,
0.0275, 0.0658,
1.038
1
.074
No. of reflections
No. of parameters
H-atom treatment
9591
294
5591
166
H-atom parameters constrained
−3
Δρmax, Δρmin (e Å )
0.579, − 0.515
1.329, − 1.585
MTPT cations form almost planar sheets, while in 3 the pack-
ing slightly more reminds the wave-like layers.
triazinium heterocycle. Although, I(1)…S(1) and I(2)…
S(1A) interactions are longer than the sum of Van der Waals
radii (3.939 Å and 4.149 Å), and in the equilibrium crystal
structure these distances are slightly increased but still the
corresponding bond critical point (bcp) and bond path for
the chalcogen bond are observed (Fig. 2). As it can be seen
from Fig. 2, the monoiodide anion also participates in a hy-
In the crystal structure of compound 2 (Fig. 1) the
monoiodide anions and MTPT cations have symmetrically
inequivalent positions in the asymmetric part of a crystal cell.
The most evident difference in crystal surrounding can be
observed in interatomic distances for the I(1) and I(2) anions
(
Fig. 1a). Two symmetrically inequivalent positions remain in
drogen bond with the atom of the CH -group.
3
the calculated structure after the equilibrium state localization:
A chalcogen bond is observed only in the case of
monoiodide 2 while in tetraiodide 3 structure the anion
is shifted away from the sulfur atom and the cation…an-
ion interactions are implemented mainly via I…H
interactions.
–
–
I(1) and I(2) have different Mulliken charges: − 0.88 e and −
.91 e, respectively. The common feature of both monoiodide
0
anions is that they form the short contacts with a great number
of hydrogen atoms (Fig. 1). Moreover, both monoiodide an-
ions are located in front of sulfur atoms, on the extension of
the C–S covalent bond of the thiol group and form the chal-
cogen bonds. Note that the most pronounced σ-hole of sulfur
manifests itself on the extension of the covalent bond with
–
Monoiodide I(1) is situated above and below C(4) and
C(4A) atoms of triazinium ring (Fig. 1b), but the position
–
–
of I(2) is shifted, so that I(2) interacts with the hydrogen
located above and below the atoms of CH -groups instead.
3

Struct Chem
Fig. 1 MTPT monoiodide: a in-layer and b inter-layer interactions in crystal structure 2
The I(1)…C(4) and I(1)…C(4A) interactions are presented
in experimental geometry with distances 3.305 and 3.415
Å, respectively. In the calculated structure these interac-
tions are aligned to 3.263 and 3.292 Å.

Struct Chem
Fig. 2 Gradient lines of electron
density, atomic basin boundaries,
bond paths in the plane I(1)-S(1)-
H(11A) of 2 illustrating the
chalcogen and hydrogen bonds
2
–
In the crystal structure of 3 (Fig. 3), oligoiodide anions I4
closed-shell interactions and covalent bonds. The descriptor
based on the ratio of maximal and minimal eigenvalues of
electron density Hessian |λ (r )|/λ (rbcp) [44] for all studied
are stretched along MTPT, and the H(4) and H(10) atoms, just
as in compound 2, form the short contacts with I(1) . The
–
1
bcp
3
interlayer interactions between the oligoiodide anion and
MTPT are represented by interactions I(2)…N(1) and I(1)…
C(4) (Fig. 3b).
polyiodide subunits give values much less than 1 (typical for
closed-shell interactions), which is consistent with the previ-
ously given interpretation for halogen bonding [45].
2–
For the oligoiodide I4 anion of 3, the central atoms have
two alternative positions. The symmetry and disorder of the
I(2) and I(3) atoms are revealed using X-ray diffraction data.
According to the literature data concerning typical
Strong covalent interaction index, SCI [46], which is the
1
/2
reciprocal value of [(1–η(rbcp))/η(rbcp)] , where η(rbcp
)
corresponds to ELF in the bond critical point, allows us
to distinguish the I–I bonding in diiodine from the I–I bond
2–
–
–
–
I4 structures [40, 41], we can interpret it as I(1) …I …I(1)
in symmetric I3 and especially from the I…I bonding in
2
with the inversion in the middle of the central I(2)–I(3) bond.
The problem of an unambiguous model of crystal structure 3
is as follows: if we treat edge positions of central iodine atoms,
we get unreal I–I bond lengths for a diiodine molecule in both
cases: firstly, 2.301 Å, which is extremely short; secondly,
asymmetric triiodide or tetraiodide anions. In Fig. 4, in
terms of the ELF distribution in the plane of a polyiodide
anion, the typical representatives of the symmetric
triiodide and the studied tetraiodide are considered. It can
clearly be seen (Fig. 4b) that the bonding between the cen-
tral I(2) and I(2A) atoms is significantly stronger than that
between the atoms in triiodide (Fig. 4a) resulting in the
3
.340 Å, which is very long. Thus, we perform spectral inves-
2–
tigation in order to reveal structural units within the I4 anion,
as well as theoretic simulation in order to achieve reasonable
atomic positions corresponding to the equilibrium state, and
then analyze the resulting electronic and spectral
characteristics.
existence of the separate I unit in the center of the
2
tetraiodide anion (Fig. 4b), while two I–I bonds in the
triiodide anion (Fig. 4a) are almost identical. The terminal
I(1) and I(1A) atoms in the tetraiodide anion (Fig. 4b) tend
to be spherically symmetric like the iodide anion and dem-
onstrate anisotropy of electronic shells only at the inner
side, due to formation of the halogen bond with the iodine
molecule. A similar question of differentiation between I–I
and I…I bonding has recently been considered for the
halogen-bonded complexes from the standpoint of electron
delocalization indices [47]. The SCI values for the bound
diiodine give significantly higher values than for the
The experimental and theoretical observations concerning
the existence of a bound diiodine molecule inside the
tetraiodide anion can be supplemented by the values of bond
descriptors based on calculated electron density at the bond
critical points, rbcp, in crystals for the typical oligoiodide sub-
units (Table 2). The distances and the values of electron den-
sity ρ(rbcp) obtained within one theoretical level of calcula-
a
b
tions allow us to characterize the shorter I –I bond in the
a
b
tetraiodide anion as the one close to the shorter I –I bond in
the asymmetric triiodide unit, and it can definitely be charac-
terized as the elongated bond of the diiodine molecule.
abovementioned cases and thus help to define the I mol-
2
ecule as the separate unit within complex oligoiodides of
different stoichiometry and composition. The identification
b
a
However, the longer I …I bond in the tetraiodide anion is
of the I subunit within oligoiodides is a very important
2
longer and weaker than the one in asymmetric triiodide
question in tasks of interpretation of experimental and cal-
culated Raman spectra, as tri- or pentaiodides demonstrate
spectral behavior that is significantly different from the
(
Table 2). One of the reasons for this fact may be formation
of two halogen bonds instead of one bond in the asymmetric
triiodide unit.
bound iodine [19]. Moreover, the existence of I dictates
2
According to [43] the ratio of potential and kinetic energy
densities, |V(rbcp)/G(rbcp)|, the relations for all considered I…I/
I–I bonds can be interpreted as intermediate ones between
the features of thermal stability and decomposition paths
[48], which is important in the design of organic matrices
for dye-sensitized solar cells.

Struct Chem
Fig. 3 MTPT tetraiodide: a in-layer and b inter-layer interactions in crystal structure 3
Experimental and calculated Raman spectra
luminescence under excitation by 632.8 or 488 nm laser lines
Fig. 5).
Unlike previously analyzed quinolinium tri- and
polyiodides [49], here a series of low-wavenumber bands
(
Experimental Raman spectra of both single crystal triazinium
salts were intense and did not demonstrate any significant

Struct Chem
Table 2 Iodine-iodine bonding characteristics in the typical oligoiodide
subunits obtained from calculations of electron density for equilibrium
geometry of listed crystals
Symmetric triiodide anion in IVOVOG [42]
a
b
a –
[
I –I –I ]
a
b
b
a
Bond
I –I
I –I
Distance
2.9875
0.0440
0.297
1.441
0.940
2.9875
0.0440
0.297
1.441
0.940
ρ(rbcp
(rbcp)|/λ
V(rbcp)|/G(rbcp)|
)
|λ
1
3
(rbcp)
|
SCI
Asymmetric triiodide anion in SEJQAC [23]
a
b
a –
[
I –I …I ]
a
b
b
a
Bond
I –I
I …I
Distance
2.8666
0.0538
0.345
1.597
1.121
3.1174
0.0344
0.247
1.266
0.731
ρ(rbcp
(rbcp)|/λ
V(rbcp)|/G(rbcp)|
)
Fig. 5 Experimental Raman spectra of monoiodide 2 and tetraiodide 3 of
MTPT
|λ
1
3
(rbcp
)
|
SCI
–
1
comparison to crystalline I with the band at 180 cm .
2
Symmetric tetraiodide anion in 3 (this work)
b
a
b
a 2–
Other low-wavenumber bands are observed nearly at the
same wavenumbers for structures 2 and 3 and in general
can be attributed to cation…anion, anion…anion and cat-
ion…cation librations as well as deformational vibrations
of some structural fragments of an organic cation. A more
detailed description has been made using calculated
Raman data for crystals 2 and 3, the comparison of exper-
imental and calculated modes, as well as their detailed
assumption, is presented in Table 3.
[
I …I –I …I ]
b
a
b
a
Bond
I –I
I …I
Distance
2.8924
0.0529
0.358
1.626
1.168
3.3690
0.0230
0.201
1.091
0.537
ρ(rbcp
(rbcp)|/λ
V(rbcp)|/G(rbcp)|
SCI
)
|λ
1
3
(rbcp)
|
Geometry optimization of crystal structure 3 also results
–
–
in the monoiodide structure is considered, thus the spec-
trum of tetraiodide 3 can be interpreted only in comparison
with corresponding monoiodide 2, as some of the bands lie
in anion organization of the I …I …I type, which is in
2
agreement with the experimental Raman data, where only
the characteristic band of the bound diiodine is observed
and no typical triiodide bands are present in the Raman
spectrum of 3.
Thus, experimental, calculated Raman spectra as well as
the descriptors based on calculated electron density allow
us to consistently characterize the bonding within the dis-
ordered tetraiodide anion. The combination of experimen-
tal and computational data identifies the existence of the
–
in the range of typical polyiodide vibrations 100–180 cm
1
.
In Fig. 5, the upper red curve corresponds to the spec-
–
1
trum of compound 3, the characteristic band at 170 cm
belonging to the I–I vibration is marked by an asterisk. It
can evidently be attributed to the region of bound diiodine
–
1
vibration (140–180 cm ) according to the literature data
19], which allows us to characterize this molecule as rath-
[
–
1
er weakly bound: 10 cm shift to lower wavenumbers in
bound I unit within the tetraiodide anion.
2
–
–
2
Fig. 4 ELF distribution in the symmetric triiodide anion in IVOVOG (a) and in the tetraiodide anion I …I …I 3 (b)

Struct Chem
Table 3 Low-frequency
experimental and calculated
modes for crystals 2 and 3
2
3
Assumption
Experiment
Calculation
112 and 119
Experiment
116
Calculation
113 and 119
119
δ of phenyl- and triazine rings with respect
to each other + δ C–S–C fragment
1
53
155
153
152
Out-of-plane δ of phenyl- and triazine
rings with respect to each other—
wave-like distortion of cation layers
–
1
2
–
170 (s)
–
163
–
υ
I-I molecule (central)
80 (w)
00
185
204
Rotation of N-CH
3
196
200
Planar δ of phenyl- and triazine rings with
respect to each other
2
30
220 and 244
231
–
–
3 3
δ of N–CH and δ of –S–CH , respectively
–
212
228 and 230
Out-of-plane δ of phenyl- and triazine
rings + δ C–S–C fragment + rotation of
3 3
–S–CH + rotation of N–CH
2
75
282
275
280 and 281
Planar δ of phenyl- and triazine
rings + δ C–S–C
3 3
fragment + δ S–CH + δ N–CH
3
24
47
331 and 334
354
325
349
334 and 336
351 and 353
Planar δ of phenyl- and triazine rings
3
Planar δ of phenyl- and triazine
rings + δ C–S–C
3
98
49
419
453
–
–
δ out-of-plane for phenyl- ring
4
445
454
3
δ C–S–C + δ N–CH + δ out-of-plane
for phenyl- and triazine rings
5
34
57
539 and 544
557
536
558
542 and 543
560 and 561
Out-of-plane δ N–N–C of triazine ring
Planar δ of triazine ring + δ C–S–C
5
Funding information The work was financially supported by the
Ministry of Education and Science of the Russian Federation, grant
Conclusions
4
.1157.2017/4.6, and by the Government of the Russian Federation,
Two crystalline products of the synthesis of 1-methyl-3-
methylthio-5-phenyl-1,2,4-triazinium iodides have made it
possible to analyze the features of non-covalent interactions
of the cation in two different crystalline environments: in
iodine-excessive and iodine-deficient structures. A strong
electron donor, like the monoiodide anion, allows formation
of the S…I chalcogen bonds, while those in the tetraiodide
structure do not exist.
Act 211, contract No. 02.A03.21.0011.
Compliance with ethical standards
Ethical statement All ethical guidelines have been adhered to.
Conflict of interest The authors declare that they have no conflict of
interest.
Joint consideration of X-ray diffraction data together with
experimental and calculated Raman data has helped to de-
scribe and characterize the bonding within the I4 anion with
the disorder of central iodine atoms in 1-methyl-3-methylthio-
2–
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