Crystal structure, spectroscopic and thermal properties of the coordination compounds M(1,3-diethyl-2-thiobarbiturate) M = Rb+, Cs+, Tl+ and NH4+

Article abstract of DOI:10.1016/j.poly.2015.05.048

Four new compounds of 1,3-diethyl-2-thiobarbituric acid (C₈H₁₁N₂O₂S, Hdetba) with Rb⁺, Cs⁺, Tl⁺ and NH₄⁺ ions were prepared by Hdetba neutralization with the metal carbonates or ammonium hydroxide in aqueous solution. The colorless crystals have been investigated using X-ray diffraction techniques, differential scanning calorimetry, thermogravimetry and infrared spectroscopy. The coordination compounds of MDetba with M = Rb, Cs and Tl crystallize in the orthorhombic space group P2₁2₁2₁, but compound NH₄Detba crystallizes in the triclinic space group P1ˉ. The MDetba structures were compared at the molecular and supramolecular levels. The Detba^- ion in the NH₄⁺ compound forms conformer (A) with two diethyl groups on one side of the ion ring, whereas the Detba^- ion in the Rb(I), Cs(I) and Tl(I) compounds forms conformer (B) with two diethyl groups on different sides of the ring. The results of IR spectroscopy and thermal analysis are consistent with the X-ray data.

Full text of DOI:10.1016/j.poly.2015.05.048

Polyhedron 98 (2015) 113–119
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Crystal structure, spectroscopic and thermal properties of the
coordination compounds M(1,3-diethyl-2-thiobarbiturate) M = Rb+, Cs+,
Tl+ and NH+4
c
d
e,f,g
Maxim S. Molokeev a,b, , Nicolay N. Golovnev , Sergey N. Vereshchagin , Victor V. Atuchin
⇑
a Laboratory of Crystal Physics, Kirensky Institute of Physics, SB RAS, bld. 38 Akademgorodok 50, Krasnoyarsk 660036, Russia
b Department of Physics, Far Eastern State Transport University, 47 Serysheva Str., Khabarovsk 680021, Russia
c Department of Chemistry, Siberian Federal University, 79 Svobodny Aven., Krasnoyarsk 660041, Russia
d Laboratory of Catalytic Conversion of Small Molecules, Institute of Chemistry and Chemical Technology, SB RAS, bld. 24 Akademgorodok 50, Krasnoyarsk 660036, Russia
e Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, 13 Lavrentiev Aven., Novosibirsk 630090, Russia
f Functional Electronics Laboratory, Tomsk State University, 36 Lenin Aven., Tomsk 634050, Russia
g Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, 2 Pirogov Str., Novosibirsk 630090, Russia
a r t i c l e i n f o
a b s t r a c t
Four new compounds of 1,3-diethyl-2-thiobarbituric acid (C8H11N2O2S, Hdetba) with Rb+, Cs+, Tl+ and
NH+4 ions were prepared by Hdetba neutralization with the metal carbonates or ammonium hydroxide
in aqueous solution. The colorless crystals have been investigated using X-ray diffraction techniques, dif-
ferential scanning calorimetry, thermogravimetry and infrared spectroscopy. The coordination com-
pounds of MDetba with M = Rb, Cs and Tl crystallize in the orthorhombic space group P212121, but
Article history:
Received 28 March 2015
Accepted 31 May 2015
Available online 14 June 2015
Keywords:
ꢀ
compound NH4Detba crystallizes in the triclinic space group P1. The MDetba structures were compared
1,3-Diethyl-2-thiobarbituric acid
Alkali ion, thallium(I) and ammonium
cations
Coordination compounds
X-ray diffraction
at the molecular and supramolecular levels. The Detbaꢀ ion in the NH4+ compound forms conformer (A)
with two diethyl groups on one side of the ion ring, whereas the Detbaꢀ ion in the Rb(I), Cs(I) and Tl(I)
compounds forms conformer (B) with two diethyl groups on different sides of the ring. The results of
IR spectroscopy and thermal analysis are consistent with the X-ray data.
Ó 2015 Elsevier Ltd. All rights reserved.
Thermal analysis
1. Introduction
Due to the presence of several potential donors, such as two
amine nitrogens, two carbonyl oxygens and a thione sulfur atom,
2-Thiobarbituric acid (H2Tba) and its derivatives from the gen-
eral class of barbiturates are known as thiobarbiturates [1]. They
have long been used as efficient depressants because of their phar-
maceutical properties [2]. The most famous of them are thiobarbi-
tal (5,5-diethyl-2-thiobarbituric acid) and thiobutabarbital (5-(2-
butyl)-5-ethyl-2-thiobarbituric acid) [3], which are used as antihy-
perthyroid and anesthetic agents, respectively. As compared to
oxybarbiturates, the specific activity of thiobarbiturates is largely
due to a higher pronounced hydrophobic nature of the sulfur atom,
as compared to the oxygen atom. The presence of a sulfur atom in
thiobarbiturate results in higher fat solubility, short duration of
action, increased hypnotic potency and accelerated metabolic
degradation [4–6].
thiobarbiturates are very interesting polyfunctional ligands in
coordination chemistry [7–25]. Thiobarbiturate coordination com-
pounds of alkali ions are used in the synthesis of pharmacologically
active organic thiobarbiturates [1,2] and may find application in
materials science [16,26]. However, up to now, they have been
poorly investigated [9,11,12,17,18,25]. According to structural
studies of alkali ion coordination compounds with 2-thiobarbituric
acid [9,12,17], the following rules are observed when progressing
down group I of the periodic system from light to heavier ele-
ments: (1) a more active trend for metal-sulfur bond formation;
(2) an increase of the alkali ion coordination number; (3) a
decrease in number of coordinated water molecules; (4) an
increase in the number of chemical bonds formed by the ligand
Htbaꢀ with metal ions. The structures of the compounds are stabi-
lized by numerous hydrogen bonds, NꢀH. . .O, NꢀH. . .S, OꢀH. . .O
and OꢀH. . .S, and
p p interactions. The coordination compounds
ꢀ
⇑
Corresponding author at: Laboratory of Crystal Physics, Kirensky Institute of
Physics, SB RAS, bld. 38 Akademgorodok 50, Krasnoyarsk 660036, Russia. Tel.: +7
391 249 45 07.
of Li+, Na+, K+ with 1,3-diethyl-2-thiobarbituric acid (C8H11N2O2S,
HDetba) [25] appreciably differ from the corresponding 2-thiobar-
biture coordination compounds. The presence of ethyl substituents
E-mail address: msmolokeev@gmail.com (M.S. Molokeev).
http://dx.doi.org/10.1016/j.poly.2015.05.048
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

114
M.S. Molokeev et al. / Polyhedron 98 (2015) 113–119
near two nitrogen atoms affects both the coordination environ-
ment of the metal ions and the supramolecular interactions.
In the present study, four new compounds, MDetba (M = Rb, Cs,
Tl and NH4), are considered their crystal structures are solved, and
their IR and thermal decomposition are analyzed. The principle
interest of the observation is to investigate the solid-state structure
variation of 1,3-diethyl-2-thiobarbiturate compounds on alkali-
metal (or NH4, Tl) substitution, and to give a comparison with
the corresponding structures of the 2-thiobarbiturate compounds.
acetone and dried in the air. The colorless crystals of 1–4, suitable
for single crystal X-ray diffraction analysis, were grown by contin-
uous filtrate evaporation at room temperature.
2.2. X-ray diffraction analysis
The intensity patterns were collected from single crystals of 1–4
at 25 °C using a SMART APEX II X-ray single crystal diffractometer
(Bruker AXS) equipped with a CCD-detector, graphite monochro-
mator and Mo K
a radiation source. Absorption corrections were
2. Experimental
applied using the SADABS program. The structures were solved by
direct methods using the package SHELXS and refined with an aniso-
tropic approach for non-hydrogen atoms using the SHELXL program
[27]. All the hydrogen atoms of the Detba– ligands in 1–3 were
positioned geometrically as riding on their parent atoms, with
d(C–H) = 0.93 Å for the C5–H5 bond, d(C–H) = 0.97 Å for all other
C–H bonds and Uiso(H) = 1.2Ueq(C). All hydrogen atoms of the
NH+4 ion in NH4Detba compound 4 were found via Fourier differ-
ence maps and refined without any constrains. The structural tests
for the presence of missing symmetry elements and possible voids
were produced using the PLATON program [28]. The DIAMOND program
was used for the crystal structure plotting [29].
2.1. Reagents and synthesis
1,3-Diethyl-2-thiobarbituric acid [CAS 5217-47-0] was com-
mercially available from Sigma–Aldrich. Rubidium and cesium car-
bonates, thallium(I) nitrate and ammonium hydroxide (analytical
grade, Acros) were used without further purification. Initially, the
thallium(I) carbonate was prepared by precipitation on addition
of excess Na2CO3 to an aqueous solution of TlNO3.
Compounds 1–4 (Table 1) were prepared by the neutralization
of 1,3-diethyl-2-thiobarbituric acid with the corresponding metal
carbonate or ammonium hydroxide in aqueous solution. The crys-
tallization of 1 and 2 was carried out from small volumes of con-
centrated aqueous solutions (pH 4–5) obtained by neutralization
of 1,3-diethyl-2-thiobarbituric acid with the corresponding metal
carbonate. For the synthesis of 3 and 4, the ligand (5.0 mmol)
was mixed with thallium(I) carbonate (2.5 mmol) or ammonium
hydroxide (5 mmol) in water (5 cm3). The mixtures were stirred
for 5 h at 22 °C to complete the reaction and precipitate the prod-
ucts. All the powders were removed by filtration, washed with
The powder X-ray diffraction data were obtained using a D8
ADVANCE (Bruker) diffractometer coupled with a VANTEC detector
and a Ni filter. The measurements were made using Cu K
a radia-
tion. The structural parameters obtained by single crystal analysis
were used as a base in the powder pattern Rietveld refinement. The
refinement was performed using the program TOPAS 4.2 [30]. The
low R-factors and good refinement results shown in Figs. 1S–4S
indicate the crystal structures of the powder samples to be repre-
sentative of the bulk structures of 1–4, respectively.
Table 1
Crystal structure parameters for 1–4.
Single crystal
RbDetba (1)
CsDetba (2)
TlDetba (3)
NH4Detba (4)
Moiety formula
Dimension (mm)
Color
Molecular weight
Temperature (K)
Space group, Z
a (Å)
C8H11N2O2RbS
0.4 ꢁ 0.07 ꢁ 0.07
Colorless
284.72
C8H11CsN2O2S
0.4 ꢁ 0.07 ꢁ 0.07
Colorless
332.16
C8H11N2O2STl
0.3 ꢁ 0.1 ꢁ 0.1
Colorless
403.62
C8H15N3O2S
0.45 ꢁ 0.45 ꢁ 0.1
Colorless
217.29
298
P-1, 2
8.472(2)
8.853(4)
8.964(2)
98.436(4)
116.059(3)
109.916(4)
531.8(3)
1.357
298
298
298
P212121, 4
4.3730(9)
14.789(3)
16.923(3)
90
90
90
1094.5(4)
1.728
4.691
P212121, 4
4.5236(9)
14.739(3)
16.937(4)
90
90
90
1129.3(4)
1.954
3.441
P212121, 4
4.3767(4)
14.7003(14)
16.6064(16)
90
b (Å)
c (Å)
a
(°)
b (°)
90
90
c
(°)
V (Å3)
1068.44(17)
2.509
15.288
qcalc (g/cm3)
l
(mmꢀ1
)
0.285
Reflections measured
8922
10638
10410
4901
Reflections independent
2265
2951
2880
2598
Reflections with F > 4
r
(F)
1853
2572
2530
2112
2hmax (°)
52.92
59.32
59.74
56.94
h, k, l - limits
ꢀ5 6 h 6 5
ꢀ18 6 k 6 17
ꢀ21 6 l 6 21
0.0586
ꢀ6 6 h 6 6
ꢀ19 6 k 6 20
ꢀ23 6 l 6 23
0.0303
ꢀ6 6 h 6 6
ꢀ19 6 k 6 20
ꢀ23 6 l 6 22
0.0353
ꢀ11 6 h 6 11
ꢀ11 6 k 6 11
ꢀ11 6 l 6 11
0.0206
Rint
Refinement results
The weighed refinement of F2
w = 1/
w = 1/
w = 1/
w = 1/
[r
2(F2o)+(0.006P)2 + 0.0P]
[r
2(F2o)+(0.0185P)2 + 0.0P]
[r
2(F2o)+(0.0P)2 + 0.0P]
[r
2(F2o)+(0.0642P)2 + 0.089P]
where P = max(F2o + 2Fc2)/3
Number of refinement
parameters
129
129
130
142
R1 [Fo > 4
wR2
r
(Fo)]
0.0343
0.0588
1.001
0.0233
0.0428
1.008
0.0263
0.0436
0.999
0.0390
0.1071
1.045
Goof
D
D
qmax (e/Å3)
0.423
0.369
0.724
0.383
qmin (e/Å3)
ꢀ0.285
ꢀ0.492
ꢀ0.806
ꢀ0.235
(D/r)
0.001
0.003
0.002
0.001
max

M.S. Molokeev et al. / Polyhedron 98 (2015) 113–119
115
2.3. Physical measurements
The C2—S bond lengths in 1–3 are in the range of 1.687–1.694 Å
(Table 1S), which exceeds the range previously found for HDetba
(1.658–1.681 Å) [31,32], and this indirectly confirms the participa-
tion of the S atom in the ligand coordination. All three compounds
have similar O1—C4, O2—C6 and C4—C5, C5—C6 bond lengths
(Table 1S), which indicates charge delocalization in the
O@CꢀCHꢀC@O group. Such delocalization was observed in alkali
and other metal compounds of 2-thiobarbiturates [9–25].
Simultaneous thermal analysis (STA) measurements were per-
formed on a Netzsch STA Jupiter 449C device with an Aeolos
QMS 403C mass-spectrometer under a dynamic argon-oxygen
atmosphere (20% O2, 50 ml minꢀ1 total flow rate). Platinum cru-
cibles with perforated lids were used and the sample masses taken
for the STA experiments were 3.9–4.1 mg for (Rb, Cs, Tl)Detba and
5.2 mg for NH4Detba. The measurement procedure consisted of a
temperature stabilization segment (30 min at 40 °C) and a dynamic
segment at a heating rate of 10 °C minꢀ1. The qualitative composi-
tion of the evolved gases was determined by on-line QMS in the
Multiple Ion Detection mode. The following predefined ions were
scanned: m/z = 18 (H2O), 28 (N2, CO), 30 (NO), 32 (O2), 44 (CO2)
and 64 (SO2). The IR absorption spectra of the compounds were
recorded over the range of 400–4000 cmꢀ1 at room temperature
on a VECTOR 22 Fourier spectrometer. The spectral resolution dur-
3.2. Comparison of the structures 4, 1–3 and MDetba (M = Na, Li, K)
The main structural characteristics of 4 are shown in Table 1.
The main obtained bond lengths are shown in Table 1S. The asym-
metric unit of the unit cell of NH4Detba contains one NH+4 ion and
one Detbaꢀ ion (Figs. 1b and 2d). The NH+4 ion is connected to four
Detbaꢀ ions by three intermolecular N–H. . .O hydrogen bonds and
one N–H. . .S bond (Table 2S, Fig. 2d). They form 2D-layers through
two C22(8) chains along the a and b axes and the rings R22(8) and
R44(16) (Fig. 3). The pattern consists of chains whose links contain
R22(8) rings. Therefore, the extended notation for this pattern is
C22(8)[R22(8)] [33]. These layers lie in the ab plane (Figs. 3, 5S) and
there are only Van-der-Waal forces between the layers. The struc-
ing the measurements was 5 cmꢀ1
.
3. Results and discussion
tural analysis reveals
p–p interactions between the Detba rings
3.1. Crystal structures of 1–3
(Table 3S, Fig. 6S). The Detbaꢀ ions adopt the ‘‘head-to-tail’’ mode
in the crystal packing [34]. The main feature that distinguishes the
Detbaꢀ ion in samples 1–3 from that in 4 is the absolute value of
the torsion angle C8–C7–C9–C10 (Table 1S). Coordination com-
pounds 1–3 have large values of ꢂ150°, but compound 4 has a
small value of ꢂ4°. Previously, such a difference was found
between the LiDetba, NaDetba and KDetba compounds (Table 1S)
[26]. The Detbaꢀ ions were found in two different conformational
states: conformer (A) in LiDetba and NaDetba, with two diethyl
groups on one side of the ion ring, and conformer (B) in KDetba,
with the diethyl groups on different sides of the ring. However,
Hdetba compounds [31,32] exist only as conformer (A). One can
find that compounds 4 and 1–3 present the Detbaꢀ ion in confor-
mational states (A) and (B), respectively.
The asymmetric unit of the MDetba (M = Rb, Cs, Tl) unit cells
contains one M+ ion and one Detbaꢀ ion (Figs. 1a, 2a–c). The crystal
structures are isostructural to that of KDetba reported earlier [25].
The M+ ion is coordinated by six Detbaꢀ ions through four O atoms
and two S atoms, forming a trigonal prism. The trigonal prisms are
linked by the base facets and form an infinite rod along the a axis.
From this analysis, the chemical names for these compounds can
be
presented
as
catena-(l6-1,3-diethyl-2-
thiobarbituratoꢀO,O,O0O0,S,S)-rubidium, cesium and thallium.
There are no intermolecular hydrogen bonds and p–p interactions.
Earlier, it was supposed that the MDetba compounds with large
M+ ions (radii equal or bigger than that of the K+ ion) tend to form
conformer (B) because they can be closer packed [25]. The present
investigation shows that compounds 1–3 also adopt conforma-
tional state (B) and this fact well agrees with the above assumption
(Fig. 7S). Compound 4 cannot be used for this purpose because the
NH+4 and Detbaꢀ ions only interact through intermolecular hydro-
gen bonding. The crystal structure of NH4Detba is different from
those of MDetba (M = Li, Na) due to the absence of a coordination
bond in 4 and differences in the hydrogen bonding. The packing of
the Detbaꢀ ions is, however, very similar for both of them (Fig. 8S).
The crystal structure of Hdetba [31,32] displays conformer (A) of
Detbaꢀ, but the packing of these ions is different from that in
MDetba (M = Li, Na, NH4).
3.3. Comparison of the structures of MDetba and MHtba
The structures of M+ metal cation coordination compounds with
Htbaꢀ and Detbaꢀ correspond to the generalized formula [M(l6
-
LꢀO,O,O0,O0,S,S]n (L = Htbaꢀ, M = K, Rb, Cs; L = Detbaꢀ, M = K, Rb,
Cs, Tl), i.e. the ligand coordination is the same in all these com-
pounds. The difference is in the coordination polyhedron structure.
So, in the compounds with Htbaꢀ it is a distorted octahedron, and
in the compounds with a Detbaꢀ it is a trigonal prism. If, similarly
to KHtba [12], the relatively large distances of Rb–S [3.898(1) Å]
and CsꢀS [3.934(3) Å] are considered in MHtba (M = Rb, Cs) [17]
as chemical bonds, then the corresponding polyhedra take the
square antiprism form (Fig. 8S), like that in KHtba [12]. However,
such long interatomic distances, apparently, should be considered
Fig. 1. MDetba schemes: (a) M = Rb, Cs, Tl (1–3); (b) M = NH4 (4).

116
M.S. Molokeev et al. / Polyhedron 98 (2015) 113–119
Fig. 2. The asymmetric unit of the MDetba unit cell: (a) M = Rb (1); (b) M = Cs (2); (c) M = Tl (3); (d) M = NH4 (4). All atoms in the asymmetric unit are labeled. The directly
neighboring symmetry-generated atoms are represented by principal ellipses with an individual color. The bonds linking asymmetric unit atoms with the symmetry-
generated atoms are represented by dashed lines, except for the intermolecular hydrogen bond in 4, which is shown with dashed lines also. The ellipsoids are drawn at the
50% probability level, except for the hydrogen atoms which are represented by arbitrary spheres. (Color online.)
Fig. 3. Hydrogen bonding in 4. The CH2–CH3 groups are deleted for clarity, the H-bonds are marked by dashed lines, the H-bond motifs are marked by circles and broad lines.
as shortened contacts. The SꢀC2 bond lengths in the compounds
under investigation coincide with the bond lengths in H2tba
[35,36] and Hdetba [31,32] within the esd. That is consistent with
the predominantly electrostatic interactions of an S atom with Cs+
and Rb+ ions, [17] as well as with other alkali ions [9,11,12]. The
C4–O1 and C6–O2 bond lengths are approximately the same,
which indicates electron density delocalization within the
C4(O1)–C5(H)–C6(O2) structural fragment. In the single known
crystalline form of Hdetba, where the molecule exists in the
thionedicarbonyl structure, the C4–O1 bond length is shorter than
the C6–O2(H) bond length by 0.045 Å [31,32]. Comparatively, in
the thionedicarbonyl form of H2tba, the difference is as high as
ꢂ0.07 Å [36].
In MDetba (M = Rb, Cs, Tl), there are no intermolecular hydro-
gen bonds. Comparatively, in MHtba (M = Rb, Cs), there are two
NꢀH. . .O H-bonds which combine Htbaꢀ ions into pairs with the
formation of an 8-membered cycle (motif R22(8)). In NH4Htba [37]
and NH4Detba, all the hydrogen atoms of the NH+4 ions are involved

M.S. Molokeev et al. / Polyhedron 98 (2015) 113–119
117
in hydrogen bond formation. In NH4Detba, there are two NꢀH. . .O
and two NꢀH. . .S hydrogen bonds, but in the NH4Htba, three
NꢀH. . .O and one NꢀH. . .S hydrogen bonds exist. In both com-
pounds, the N–H. . .O hydrogen bonds form 8-membered cycles
(motif R22(8)), which exist as isolated elements in NH4Detba or gen-
erate infinite chains from Htbaꢀ ions in NH4Htba.
is (49.86) (Fig. 4a). To the best of our knowledge, there is no literary
information about polymeric compounds with such a Schläffli
symbol. The 6-connected 3D net (49.66), known as the ‘‘acs’’ net,
which was observed for the ammonium 1,3-dimethylbarbiturate
compound, [39] is the most similar to the net observed for
MDetba (M = Cs, Rb, Tl) (Fig. 4b). However, it should be noted that
the 3D-net in the 1,3-dimethylbarbiturate compound is formed by
H-bonds instead of bonds between a metal ion and an anion.
Similarly, the net of compound 4 can be plotted using the H-bond-
ing (Figs. 3 and 4c). The Detbaꢀ and NH+4 ions act as 4-connected
nodes and topologically they are equivalent. The Schläffli symbol
of this uninodal four-connected 2D net is (43.63) (Fig. 4c). Such a
2D bilayer honeycomb topological network ‘‘hcb’’ was also found
for the compounds Zn(Ata)2 [40] (Hata = 5-amino-1H-tetrazole)
and Zn2(Atz)3(N3)ꢃH2O compound [41] (Atz = 5-amino-tetrazolate),
and the authors wrote that such a 2D arrangement with mixed
polygones had rarely been observed [41]. It is worth mentioning
that a 4-connected 2D net with the (42.64) Schläffli symbol, which
is also rarely observed and close to (43.63), was found for MDetba
(M = Li, Na) (Fig. 4d). Therefore, the compounds under investiga-
tion are significant from a topological point of view, and coordina-
tion compounds of Detba with different metals could be promising
in the search for exotic topological nets.
3.4. Topological analysis
One of the most powerful techniques in crystal engineering is
the reduction of crystal structures to networks (nets), and then
topological analysis can be used to understand the nature of frame-
work [38]. To simplify the analysis and net representation, in the
present analysis all the molecules were considered as spheres
which were located at the molecules’ center of gravity. As com-
pounds 1–3 are isostructural, one net can represent all these com-
pounds. In these compounds, the Cs+, Rb+, Tl+ ions are linked by six
Detbaꢀ ligands and each Detbaꢀ ligand bridges six Cs, Rb or Tl ions.
Therefore, from a topological point of view, the Detbaꢀ ligand acts
as a six connecting node and the Cs+, Rb+ and Tl+ ions act as a six-
connected node. Although the two nodes are chemically different,
in our case the two nodes are topologically equivalent, and thus,
the Schläffli symbol for this uninodal six-connected 3D network
Fig. 4. The schematic representation of the network topology of: (a) MDetba (M = K, Rb (1), Cs (2), Tl (3)); the Detbaꢀ ligand is represented by purple spheres, the M ions are
represented by gray spheres; (b) the ammonium 1,3-dimethylbarbiturate compound, the 1,3-dimethylbarbiturate ligand is represented by purple spheres and NH4 ions are
represented by blue spheres; (c) NH4Detba (4): the Detbaꢀ ligand is represented by gray spheres and NH4 ions are represented by blue spheres; (d) MDetba (M = Li, Na): the
Detbaꢀ ligand is represented by purple spheres, the M ions are represent by gray spheres. (Color online.)

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M.S. Molokeev et al. / Polyhedron 98 (2015) 113–119
3.5. IR spectroscopy
The IR spectra of 1–3 contain two very strong bands in the nar-
row ranges of 1611–1614 and 1655–1658 cmꢀ1, in the region for
C–O stretching vibrations, as shown in Fig. 9S. For pure Hdetba,
the
is consistent with ligand coordination through the oxygen atoms.
The positions of strong
(CO) bands at 1621 and 1596 cmꢀ1 in
m
(CO) bands are located at 1646 and 1521 cmꢀ1. The difference
m
the IR spectrum of 4 are also different from those observed for
Hdetba; but this is due to their participation in N–H. . .O hydrogen
bonds (Fig. 3). The similarity of the IR spectra of compounds 1–3,
particularly in the range of 1700–470 cmꢀ1, confirms that these
compounds are isostructural. Some differences in the m(NH) oscil-
lations of compounds 1–4 can be attributed to the different
strengths of the formed hydrogen bonds. The strong band at
1155 cmꢀ1 in the IR spectrum of Hdetba, which by analogy with
H2tba [42,43] can be attributed to the m(C@S) vibration, is very
weak in the IR spectra of the compounds, in accordance with ligand
coordination through the donor sulfur atom in 1–3. The attenua-
tion of this band intensity in the IR spectrum of compound 4 is
probably due to the participation of the S atom in the NꢀH. . .S
hydrogen bond (Fig. 3), which is absent in Hdetba [31,32].
Therefore, the results of the IR spectroscopy are consistent with
the X-ray data.
3.6. Thermal decomposition of 1–4
Two different decomposition/oxidation patterns were observed
for compounds 1–4.
3.6.1. Thermal decomposition of (Rb, Cs, Tl)Detba
The TG and DSC thermal decomposition curves of 1 and 2
resemble those reported earlier for the K-containing compound
[25] and four main conversion regions located at T > 250 °C are
revealed, as shown in Figs. 5a, b, 10S and Table 4S. An additional
slightly endothermic process occurs for 2 at 120–240 °C; no ion
appearance was observed by means of mass-spectroscopy. Most
probably, this accounts for elimination of unreacted Detba, which
is present in the synthesized sample as an impurity at a level of
ꢂ2.92 wt.%. The total experimental mass loss was found to be
41.36% (including ꢀ2.92 wt.% Hdetba) for the sample heated at
600 °C. To estimate the pure 2 decomposition stoichiometry, the
thermal data were corrected assuming a 97.08% purity of com-
pound 2 (Fig. 5b).
As for TlDetba (3), for safety reasons, the temperature ramp for
TlDetba was restricted to prevent a thallium carry-over and the
experiment was stopped just after the beginning of the decompo-
sition/oxidation at 252 °C (Fig. 11S).
Fig. 5. TG (1), DSC (2) and DTG (3) curves of the thermal decomposition of RbDetba
(a), CsDetba (b) and NH4Detba (c) in a dynamic argon-oxygen atmosphere (20% O2),
b = 10 °C minꢀ1
.
The temperature of the beginning of thermal conversion
decreases in the sequence 1–3; the first two stages are low-
exothermic (Table 4S, stages 1 and 2). These stages proceed as
the thermal decomposition of organic moiety without pronounced
oxidation. Comparatively, the following stages include deep hydro-
carbonaceous and carbonaceous residue oxidation (Table 4S, stages
3 and 4). It should be noted that the carbonaceous matter, which is
oxidized at stage 4, contains an amount of nitrogen and sulfur, but
not hydrogen. The total mass losses for RbDetba and CsDetba can
transformation of 1 and 2 to the corresponding Rb2SO4 and
Cs2SO4 sulfates. This mass unbalance can be provisionally
explained by differences in the thermal treatment conditions for
the bulk and DSC runs and the incomplete transformation in the
case of DSC.
3.6.2. Thermal decomposition of NH4Detba
be
estimated
as
ꢀ50.73%
and
ꢀ39.6%,
respectively
The thermal decomposition process of 4 may be divided into
two stages. The first endothermic mass loss is situated at 100–
(Fig. 5a and b). As was shown earlier, the principle oxidative
decomposition products of Ca/Sr thiobarbiturates [15] and
KDetba [25] are the corresponding metal sulfates. Similar to these
results, XRD analysis of the bulk CsDetba calcination (600 °C, 1 h,
air) residue indicates the formation of Cs2SO4 as a single crystalline
product (Fig. 12S). However, the experimental values of
175 °C (Tm = 160 °C,
D
m is ꢂꢀ14%), as evident from Fig. 5c. The
mass decrease is accompanied by an enhancement of the intensity
of ions with m/z = 17 (Fig. 13S), which is specific for the ammo-
nium mass-spectrum. Therefore, it may be concluded that the first
conversion step is decomposition of 4 to NH3 and free Hdetba,
which partly vaporizes at T > 120 °C, as we have demonstrated ear-
lier [25]. The overlap of these two processes is the reason for a
D
m = ꢀ50.73% and ꢀ39.60% obtained from the TG curve are lower
than the calculated mass losses ꢀ53.12% and ꢀ45.5% for the

M.S. Molokeev et al. / Polyhedron 98 (2015) 113–119
119
substantial excess of the experimental value
ence to the theoretical value
tion of NH3 elimination from 4 on heating.
The second transformation step is most probably the endother-
mic vaporization of the formed acid, accompanied by decomposi-
tion of the organic moiety at high temperatures, as shown in
Figs. 5c and 13S. The endothermic process of the mass loss (about
90%) is observed at 175–240 °C, and the exothermic carbonaceous
D
m ꢂ ꢀ14% in refer-
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
D
m = ꢀ7.8%, calculated for the reac-
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.poly.2015.05.048.
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Appendix A. Supplementary data
CCDC 1, 2, 3, 4 contain the supplementary crystallographic data
for 1043911, 1043909, 1043912, 1043910. These data can be