Synthesis, characterization, thermogravimetry, and structural study of uranium complexes derived from dibasic S-alkylated thiosemicarbazone ligands

Article abstract of DOI:10.1080/00958972.2014.936860

Two pentagonal bipyramidal complexes, ethanol-(S-ethyl-N¹,N ⁴-bis(3-methoxy-2-hydroxybenzaldehyde)-isothiosemicarbazide-N,N',O, O')-dioxidouranium(VI) (1) and ethanol-(S-ethyl-N¹-(2- hydroxyacetophenone)-N⁴-(5-bromo-2-hydroxybenzaldehyde)- isothiosemicarbazide-N,N',O,O')-dioxidouranium(VI) (2), have been prepared and characterized. Their structures have been determined by X-ray crystallography, and the structural parameters are discussed with those observed in related complexes. Electronic absorption, proton magnetic resonance, and FT-IR spectra have been recorded and analyzed. In both complexes, the U(VI) centers are surrounded by N₂O₂ donor ligands, two oxido groups, and one ethanol in a distorted pentagonal bipyramid. The thermal stability of the new complexes has also been determined. 2014

Full text of DOI:10.1080/00958972.2014.936860

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Synthesis, characterization,
thermogravimetry, and structural study
of uranium complexes derived from
dibasic S-alkylated thiosemicarbazone
ligands
Ahad Fasihizada, Tahere Baraka, Mehdi Ahmadia, Michal Dusekb &
Michaela Pojarovab
a Research and Development Division of Maral Corporation,
Mashhad, Iran
b Institute of Physics of the ASCR, Prague, Czech Republic
Accepted author version posted online: 20 Jun 2014.Published
online: 18 Jul 2014.
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To cite this article: Ahad Fasihizad, Tahere Barak, Mehdi Ahmadi, Michal Dusek & Michaela
Pojarova (2014) Synthesis, characterization, thermogravimetry, and structural study of uranium
complexes derived from dibasic S-alkylated thiosemicarbazone ligands, Journal of Coordination
Chemistry, 67:12, 2160-2170, DOI: 10.1080/00958972.2014.936860
To link to this article: http://dx.doi.org/10.1080/00958972.2014.936860
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Journal of Coordination Chemistry, 2014
Vol. 67, No. 12, 2160–2170, http://dx.doi.org/10.1080/00958972.2014.936860
Synthesis, characterization, thermogravimetry, and structural
study of uranium complexes derived from dibasic S-alkylated
thiosemicarbazone ligands
AHAD FASIHIZAD†, TAHERE BARAK†, MEHDI AHMADI*†, MICHAL DUSEK*‡
and MICHAELA POJAROVA‡
†Research and Development Division of Maral Corporation, Mashhad, Iran
‡Institute of Physics of the ASCR, Prague, Czech Republic
(Received 11 March 2014; accepted 4 May 2014)
Two pentagonal bipyramidal complexes, ethanol-(S-ethyl-N1,N4-bis(3-methoxy-2-hydroxybenzalde-
hyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (1) and ethanol-(S-ethyl-N1-(2-hydroxy-
acetophenone)-N4-(5-bromo-2-hydroxybenzaldehyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidourani-
um(VI) (2), have been prepared and characterized. Their structures have been determined by X-ray
crystallography, and the structural parameters are discussed with those observed in related complexes.
Electronic absorption, proton magnetic resonance, and FT-IR spectra have been recorded and ana-
lyzed. In both complexes, the U(VI) centers are surrounded by N2O2 donor ligands, two oxido groups,
and one ethanol in a distorted pentagonal bipyramid. The thermal stability of the new complexes has
also been determined.
Keywords: Uranium complex; Isothiosemicarbazone; Crystallography; Spectra; Thermal stability
1. Introduction
Schiff base ligands have attracted much consideration in coordination chemistry because of
the application of their complexes in medicine, catalysis, nonlinear optics, magnetism, and
luminescence [1, 2]. Among the Schiff base ligands, tetradentate N2O2 donor Salen-type
compounds show applications in the fields of catalysis and nonlinear optical properties
[3, 4].
*Corresponding authors. Email: mehdieahmadi@ymail.com (M. Ahmadi); dusek@fzu.cz (M. Dusek)
© 2014 Taylor & Francis

Uranium thiosemicarbazone complexes
2161
An important feature of the tetradentate N2O2 donors is their ability to form stable com-
plexes with uranium salts [5]. Due to very strong bonding between donors of these ligands
and the uranyl group, complex formation leads to high precipitation. Thus, these com-
pounds are of importance for separation of actinides of lanthanides from nuclear waste [6].
Some tetradentate N2O2 donors can be synthesized by template reaction of S-alkyl isothi-
osemicarbazones and salicylaldehyde analogs in the presence of transition metal ions Fe
(III), Ni(II), Zn(II), Cu(II), Co(II), Pd(II), VO(II), and UO2(II) [7]. Several studies have
shown that the template synthesis of N2O2 donor isothiosemicarbazone derivatives with
UO2(II) is effective for complex formation [8].
In this study, we report the preparation of two new complexes of UO2(II) from tetraden-
tate bis-isothiosemicarbazone ligands within our search for compounds for possible applica-
tion in the separation of actinides from lanthanides. The crystallization from solution led to
pure solid complexes suitable for X-ray measurements. New complexes were characterized
by molar conductivity, CHN analysis, FT-IR, and UV–vis spectroscopy as well as with
X-ray crystallography. Thermogravimetric analysis is also provided.
2. Experimental
2.1. Experimental and instrumentation
H2L1 (3-methoxy-2-hydroxybenzaldehyde S-ethyl isothiosemicarbazone) was prepared
according to our previous report [9]. Other chemicals were of analytical grade and used
without purification. FT-IR with samples prepared as KBr pellets; UV–vis at 2 × 10−5 M L−1
1
concentration in EtOH; H NMR spectra in DMSO-d6; carbon, hydrogen, and nitrogen
microanalyses; and Electric conductance measurements were carried out, respectively, on a
FT-IR 8400-SHIMADZU spectrophotometer, a SHIMADZU model 2550 UV–vis spectro-
photometer, a Bruker BRX 100 AVANCE spectrometer, a Thermo Finnigan Flash Elemental
Analyzer 1112EA instrument, and a Metrohm 712 Conductometer.
2.2. X-ray single-crystal diffraction
X-ray diffraction data were collected at 120 K with a four-circle diffractometer Gemini of
Oxford Diffraction, Ltd., using a sealed X-ray tube with a copper anode. The primary beam
was monochromated and collimated with mirrors using the Enhance-Ultra collimator; the
diffracted beam was detected with a CCD detector Atlas. Standard data collection strategy
of CrysAlis PRO [Agilent Technologies, (2012) CrysAlis PRO. Yarnton, Oxfordshire, Eng-
land] was used for data collection as well as for data processing. Because of the strong
absorption (μ ~ 20 mm−1), the absorption correction was done carefully combining the cor-
rection based on the crystal shape with the one based on the spherical harmonic functions.
Crystallographic data are provided in table 1.
The structure was solved by charge flipping using the program Superflip [10], which is
part of the program Jana2006 [11]. The structure was refined with ShelXle [12].
Hydrogens attached to carbon were kept in the geometrically derived positions at 0.96 Å
from their parent atoms, with isotropic displacement parameter defined as a 1.5 multiple of
the parent terminal methyl carbon’s Ueq and 1.2 multiple of the other carbons.

2162
A. Fasihizad et al.
Table 1. Crystallographic data.
Crystal data
Chemical formula
Mr
C21H25N3O7SU
701.53
C20H22BrN3O5SU
734.41
Crystal system, space group
Temperature (K)
a, b, c (Å)
Triclinic, P-1
120
8.9722(2), 10.6284(3), 13.4283(3)
Triclinic, P-1
120
9.5571(3), 11.6509(4),
12.1926(4)
71.762(3), 67.775(3),
67.697(3)
α, β, γ (°)
68.272(3), 76.474(2), 76.785(2)
V (Å3)
Z
1142.16(5)
2
1139.77(6)
2
Radiation type
Cu Kα
21.28
Cu Kα
23.27
μ (mm−1
)
Crystal size (mm)
0.30 × 0.20 × 0.10
0.20 × 0.11 × 0.06
Data collection
Diffractometer
Absorption correction
Xcalibur, Atlas, Gemini ultra diffractometer
Numerical + Multi-scan; CrysAlis PRO, Agilent
Technologies, Version 1.171.36.32
0.241, 1.000
Tmin, Tmax
0.00085, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
Rint
18,743, 4010, 3970
19,211, 4004, 3818
0.052
0.597
0.054
0.597
(sin θ/λ)max (Å−1
)
Refinement
R[F2 > 2σ(F2)], wR(F2), S
No. of reflections
No. of parameters
No. of restraints
0.032, 0.085, 1.20
4010
256
8
0.024, 0.062, 1.05
4004
287
0
H-atom treatment
H atoms treated by constrained refinement
H atoms treated by
constrained refinement
1.28, −1.65
Δρmax, Δρmin (e Å−3
)
1.65, −2.32
For 1, the disorder of the central bridge was modeled. Two different positions with partial
site occupancies 0.8 and 0.2 were found in the maps of electron density. Disordered frag-
ments were then placed in appropriate positions, and all distances between neighboring
atoms were restrained as well as angles. Site occupancies were refined for the different parts
with the same thermal parameters for the same atoms in various fragments.
2.3. Synthesis of 2-hydroxyacetophenone S-ethylisothiosemicarbazone (H2L2)
Thiosemicarbazide (0.91 g, 10 mM) and ethyl iodide (1.71 g, 11 mM) were refluxed in etha-
nol for 3 h until a colorless solution was obtained. Five milliliters ethanolic solution of
2-hydroxyacetophenone (1.36 g, 10 mM) was added and the reflux continued for an extra
hour. Finally, Na2CO3·10H2O (5.72 g, 20 mM) dissolved in 10 mL water was added to
neutralize the produced hydrogen iodide. The neutralization reaction was controlled by pH
paper. The light yellow precipitate that separated was washed several times with cold ethanol.
Yield: 2.13 g (90%). M.p. 198 °C. Anal. Calcd for C11H15N3OS (237.32 g M−1): C,
55.67; H, 6.37; N, 17.71. Found (%): C, 54.24; H, 6.34; N, 17.34. IR (KBr) cm−1:
ν
asy(NH2) 3341vs; νsy(NH2) 3234 ms; ν(OH) 3002vs; ν(CH) 2935–3000vw; ν(C=N) +
ν(C=C)1624s, 1582vs, 1543s; ν(C=C) + δipb(OH) + δ(NH2) 1465s, 1415m; ν(CO) 1253s;
1
ν(N=C–N) 1234m; δoopb(OH) 743m; δoopb(CH)aromatic 698w; ν(CSC) 613w. H NMR (100

Uranium thiosemicarbazone complexes
2163
MHz, DMSO-d6): δ = 11 (s, 1H, OH; exchanges with D2O), 7.9 (d, 1H, C5), 7.6 (dd, 1H,
C3), 7.2 (dd, 1H, C4), 6.8 (d, 1H, C2), 4 (s, 2H, NH2; exchanges with D2O), 3.1 (q, 2H,
C10), 1.3 (t, 3H, C11), 0.9 (s, 3H, C8). UV/vis (ethanol) λmax nm (log ε, L M−1 cm−1): 232
(4.95), 304 (4.81), 343 (4.96). Molar conductivity (1.0 × 10−3 M; EtOH): 12 Ω−1 cm2 M−1.
2.4. Synthesis of ethanol-(S-ethyl-N1,N4-bis(3-methoxy-2-hydroxybenzaldehyde)-
isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (1)
Five milliliters ethanolic solution of 3-methoxy-2-hydroxybenzaldehyde S-ethyl isothiose-
micarbazone (0.253 g, 1 mM) and 3-methoxy-2-hydroxybenzaldehyde (0.15 g, 1 mM) was
mixed for 30 min. To the mixture, UO2(OAC)2·2H2O (0.424 g, 1 mM) was added as solid.
The red solution was obtained immediately and was refluxed for 30 min at 60 °C. Crystals
suitable for X-ray analysis were obtained by slow evaporation of the solution in the refriger-
ator after one week.
Yield: 0.53 g (75%). M.p. 234 °C. Anal. Calcd for C21H25N3O7SU (701.53 g M−1): C,
35.95; H, 3.59; N, 5.99. Found (%): C, 36.04; H, 3.43; N, 5.87. IR (KBr) cm−1:
ν(OH)alcohol 3213 m; ν(CH) 2935–3000w; ν(C=N) + ν(C=C) 1612vs, 1543s; ν(C=C) 1464m,
1435s; ν(CO) 1241 m; ν(N=C–N) 1234ms; νasy(trans-UO2) 910s; νsy(trans-UO2) 877m;
1
δ
oopb(CH)aromatic 710m; ν(CSC) 613w. H NMR (100 MHz, DMSO-d6): δ = 13 (s, 1H, OH;
exchanges with D2O), 8.6 (s, 1H, CH=N), 8.3 (s, 1H, CH=N), 7.9–6.7 (m, 6H, aromatic
protons), 4.3 (q, 2H, CH2, alcohol), 3.8 (s, 3H, CH3, alcohol), 3.5 (s, 6H, OCH3), 3.2
(q, 2H, CH2, S-ethyl), 1.3 (t, 3H, CH3, S-ethyl). UV/vis (ethanol) λmax nm (log ε,
L M−1 cm−1): 235 (4.82), 312 (4.13), 360 (3.38), 421 (4.43), 456 (3.45). Molar conductivity
(1.0 × 10−3 M; EtOH): 4 Ω−1 cm2 M−1.
2.5. Synthesis of ethanol-(S-ethyl-N1-(2-hydroxyacetophenone)-N4-(5-bromo-2-
hydroxybenzaldehyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (2)
Five milliliters ethanolic solution of 2-hydroxyacetophenone S-ethylisothiosemicarbazone
(0.237 g, 1 mM) and 5-bromo-2-hydroxybenzaldehyde (0.2 g, 1 mM) was mixed for 30 min.
To the mixture, UO2(OAC)2·2H2O (0.424 g, 1 mM) was added as solid. The red solution
was obtained immediately and was refluxed for 30 min at 60 °C. Crystals suitable for X-ray
analysis were obtained by slow evaporation of the solution in the refrigerator after one
week.
Yield: 0.46 g (62%). M.p. 223 °C. Anal. Calcd for C20H22BrN3O5SU (734.40 g M−1): C,
32.71; H, 3.02; N, 5.72. Found (%): C, 32.04; H, 3.14; N, 5.47. IR (KBr) cm−1:
ν(OH)alcohol 3213m; ν(CH) 2935–3000w; ν(C=N) + ν(C=C)1602s, 1562s; ν(C=C) 1453 m,
1423s; ν(CO) 1235m; ν(N=C–N) 1221ms; νasy(trans-UO2) 919s; νsy(trans-UO2) 885m;
1
δ
oopb(CH)aromatic 698m; ν(CSC) 613w. H NMR (100 MHz, DMSO-d6): δ = 12.8 (s, 1H,
OH; exchanges with D2O), 8.2 (s, 1H, CH=N), 7.8–6.65 (m, 7H, aromatic protons), 4.2
(q, 2H, CH2, alcohol), 4 (s, 3H, CH3, alcohol), 3.2 (q, 2H, CH2, S-ethyl), 1.3 (t, 3H, CH3,
S-ethyl), 1.1 (s, 3H, C16H3). UV/vis (ethanol) λmax nm (log ε, L M−1 cm−1): 238 (4.86), 308
(4.43), 355 (4.02), 402 (4.12), 460 (3.96). Molar conductivity (1.0 × 10−3 M; EtOH):
6 Ω−1 cm2 M−1.

2164
A. Fasihizad et al.
3. Results and discussion
The template reactions of H2L1 and 3-methoxy-2-hydroxybenzaldehyde as well as H2L2
and 2-hydroxyacetophenone with hydrated dioxidouranium(II) acetate in ethanol gave two
new complexes of uranium(VI). The complexes are stable in air, fairly soluble in methanol,
ethanol, DMF, and DMSO; sparingly soluble in acetone and diethyl ether; and insoluble in
water and n-hexane. The analytical data are in accord with the proposed structures. The
molar conductivity data are consistent with the nonelectrolytic nature of the compounds
[13].
3.1. X-ray crystallography
Single-crystal X-ray diffraction provided insight into the structure of the complexes. Their
plots with the atom labeling are shown in figures 1 and 2. Selected bond lengths and angles
are given in table 2. In both complexes, the bis-isothiosemicarbazone ligands coordinate as
tetradentate N2O2 donors, chelating to the uranyl ions. The equatorial positions are occupied
by the tetradentate ligands and oxygen of coordinated solvent. The apical positions of the
strongly distorted pentagonal-bipyramid are completed by uranyl oxygens.
Figure 1. View of 1 showing the atomic numbering and 50% probability displacement ellipsoids.

Uranium thiosemicarbazone complexes
2165
Figure 2. View of 2 showing the atomic numbering and 50% probability displacement ellipsoids.
Table 2. Selected bond distances (Å) and angles (°) of 1 and 2.
Type
1
2
Type
1
2
U1–O1
U1–O2
U1–O3
U1–O4
U1–O5
U1–N1
U1–N3
N1–C7
N3–C9
N2–C8
N1–C8
N3–N2
C1–O3
C15–O4
C20–O5
S–C8
1.787(6)
1.800(6)
2.284(4)
2.232(4)
2.454(4)
2.54(1)
2.49(4)
1.30(1)
1.30(2)
1.31(2)
1.773(4)
1.777(4)
2.255(4)
2.263(4)
2.410(4)
2.588(5)
2.535(4)
1.315(7)
1.300(6)
1.287(7)
1.413(5)
1.416(7)
1.305(7)
1.339(5)
1.446(5)
1.758(6)
1.811(5)
1.487(8)
1.432(6)
1.415(8)
1.471(8)
1.420(8)
O1–U1–O2
N3–U1–N1
N1–U1–O3
O3–U1–O5
O5–U1–O4
O4–U1–N3
O1–U1–N3
O1–U1–N1
O1–U1–O3
O1–U1–O5
O1–U1–O4
O2–U1–N3
O2–U1–N1
O2–U1–O3
O2–U1–O5
O2–U1–O4
N3–U1–O5
N1–U1–O5
O3–U1–O4
U1–O3–C1
U1–O4–C15
177.4(2)
62.4(4)
70.7(3)
77.8(2)
78.8(2)
70.6(3)
87.5(4)
91.2(3)
88.5(2)
89.7(2)
91.6(2)
92.9(4)
86.7(3)
89.4(2)
91.3(2)
91.0(2)
149.1(3)
148.4(3)
156.6(2)
134.5(4)
147.2(3)
176.4(2)
62.9(1)
70.8(1)
78.9(1)
80.1(1)
70.1(1)
84.3(2)
98.5(2)
86.2(2)
94.5(1)
89.5(2)
92.8(2)
82.0(2)
97.4(2)
86.9(1)
87.5(2)
150.2(1)
145.9(1)
158.1(1)
145.4(3)
121.5(3)
1.42(2)
1.41(1)
1.305(7)
1.335(6)
1.427(9)
1.73(1)
1.802(8)
1.53(2)
1.435(8)
1.409(9)
1.451(7)
1.389(5)
S–C17
C17–C18
C7–C6
C6–C1
C9–C10
C10–C15
The U1–O3 and U1–O4 bond distances in the complexes are shorter than U1–N1 and
U1–N3 distances, whereas the deprotonated oxygen is typically a stronger donor than the
azomethine nitrogen. This may also be due to the electronic influence imposed by the

2166
A. Fasihizad et al.
anionic trans ligands [7]. The U–O(phenolic) and U–N(imine) bond lengths are similar to
the previously observed values in this class of uranium(VI) complexes. The U=O bond dis-
tances are from 1.746(5) to 1.770(8) Å, much shorter than the equatorial U–O bond lengths,
indicating multiple bond order. The U=O bond distances are in accord with the average
value [8]. N2 and C8 are significantly out of the pentagonal plane, as indicated by the tor-
sion angle N1C8N2N3 = 3.55° in 1 and 2.98° in 2. N2 and C8 deviate, respectively, from
this plane by 0.344 and 0.257 Å in 1, and 0.551 and 0.342 Å in 2. The central ions in 1 and
2 deviate from the pentagonal plane by 0.013 and 0.032 Å, respectively.
The angles around U are not equivalent and are 62.4(4)°–78.8(2)° for 1 and 62.9
(1)°–80.1(1)° for 2, thus departing from the angle 72° in an ideal pentagon. The distortion
of ideal pentagonal-bipyramidal geometry is also manifested by the O(oxo)–U–O,N angles
ranging from 86.7(3)° to 92.9(4)° for 1 and 82.0(2)° to 98.5(2)° for 2. The dihedral angle
between the UN2O3 plane and the plane including the metal and the two axial O atoms is
89.78° for 1 and 89.48° for 2.
The dihedral angles 22.33° and 52.38° for the phenolic parts of the ligands show propel-
ler-like conformation of these moieties. These values are higher than the earlier reported
values [13]. Such distortion in the uranium complexes, including bis-isothiosemicarbazones,
may occur due to the large radius of uranium without putting significant strain on the back
bone of the ligand [14].
The intermolecular hydrogen bonds present in the complexes are summarized in table 3.
In both cases, the molecules have donor and acceptor groups and form centrosymmetric
dimers, through an interaction between O–H donors of the coordinated solvent and the
phenolato O– acceptor. The ring patterns are R2 (14) for 1 (figure 3) and R2 (8) for 2
2
2
(figure 4).
3.2. Spectral properties
Asymmetric and symmetric vibrations of the NH2 groups are observed at 3234–3521 cm−1
in the infrared spectra of the ligands. Their absence in FT-IR spectra of the complexes sug-
gests successful template reactions [15]. FT-IR spectra of the ligands display a broad band
at 3000–3132 cm−1, due to ν(OH). After coordination, the stretching vibration of the OH
also disappears. The coordination of the azomethinic nitrogens to the metal centers is
accompanied with a shift of ν(C=N) + ν(C=C) in the IR spectra to lower frequency [16].
The ν(CO) band is also shifted to lower frequency, indicating that the phenolic oxygens
take part in coordination. Finally, bands due to νasy(trans-UO2) and νsy(trans-UO2) are at
910 and 877 cm−1 in 1 and at 919 and 885 cm−1 in 2 [8].
1H NMR spectra of the compounds were recorded in DMSO-d6. The signals of the
azomethinic protons of the complexes are at lower fields than the ligands, showing
increased electron density after complexation. The chemical shift of the OH of ethanol in
1
the H NMR spectra of the complexes shows that the solvents are coordinated. Signals due
to phenolic protons are not observed in the spectra of the complexes, indicating that the
Table 3. Hydrogen bond distances (Å) and angles for 1 and 2.
D–H…A
d(D–H)
d(H…A)
\(DHA)
Complex 1
Complex 2
O–H…O
O–H…O
2.787
2.616
0.793
0.769
2.060
1.869
152.47
163.33

Uranium thiosemicarbazone complexes
2167
Figure 3. Centrosymmetric H bonded dimer in 1. H bonds are represented by dashed thick lines.
coordination takes place through oxygen. The aromatic proton signals are observed as mul-
tiplets at 7.9–6.7 ppm in 1 and at 7.8–6.65 ppm in 2. The signals related to S-ethyl moieties
appear at the same chemical shifts in both spectra of the ligands and complexes, since sulfur
does not participate in complexation.
Electronic spectra of the compounds were recorded in ethanol. The UV–vis spectra of
the ligands show the π→π* transitions near 230 nm. This band displays red shift in the
spectra of the complexes [17]. The azomethine and isothioamide n→π* transitions are at
300 and 340 nm in spectra of the free ligands. The complexes display these peaks at 310
and 360 nm with red shifts ascribed to coordination of azomethine fragment. The charge
transfer bands assigned to N→M and O→M occur at 421 nm (4.43) and 456 nm (3.45) for
1 and at 402 nm (4.12) and 460 nm (3.96) for 2 [15].
3.3. TGA study
TG analyses were performed from 27 to 1000 °C. Thermal decompositions of 1 and 2 occur
at 245–494 °C and 220–507 °C, respectively, with the proposed mechanisms shown in
scheme 1.
The thermal decomposition of 1 takes place in four steps (theoretical values in parentheses).
The 6.3% (6.5%) weight loss corresponding to loss of ethanol occurs at 245–263 °C. The

2168
A. Fasihizad et al.
Figure 4. Centrosymmetric H bonded dimer in 2. H bonds are represented by thick lines.
second step with weight loss of 8.7% (8.7%) at 263–312 °C is attributed to loss of the
S-ethyl moiety. Two OMe fragments separate at 342–368 °C with weight loss of 9%
(8.8%). Finally, the remainder of the organic part is lost at 408–494 °C (weight loss of
38.5% (40%)). The residue is U3O8 with the residual weight 38.5% (40%), which is stable
above 494 °C.
The TGA shows that 2 decomposed in three stages. Simultaneous, losses of S-ethyl frag-
ment and ethanol occur at 220–341 °C with a weight loss of 14.9% (14.6%). The halide
with a weight loss of 10.9% (10.9%) takes place at 367–383 °C. The third stage is a slow
process occurring at 392–507 °C, which is due to loss of the remainder of the ligand with a
weight loss of 41% (40.2%). The final residue is U3O8 as indicated by the residual weight
of 39% (38.2%), which is stable above 507 °C.

Uranium thiosemicarbazone complexes
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Scheme 1. The proposed mechanisms for the thermal decomposition of uranium complexes.

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A. Fasihizad et al.
4. Conclusion
Two new uranium(VI) complexes were prepared by template reactions of UO2(OA-
C)2·2H2O, isothiosemicarbazone, and an aldehyde. The complexes were air-stable and non-
electrolytes in EtOH. The complexes were characterized by CHN, FT-IR, UV–vis, 1H
NMR, and TGA as well as X-ray crystallography. It was found that the complexes were
[UO2L·EtOH], where L is dibasic N2O2 donor. The ligands are ONNO quadridentate and
coordinated to metal centers as dianion chelates. The thermal decomposition of the
complexes by TGA analyses showed that the complexes were stable to 230 °C, and after
complete decomposition, metal oxide U3O8 remained as the residue above 500 °C.
Supplementary material
CCDC 990588 and 990589 contain the supplementary crystallographic data of the com-
plexes. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Center, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: (+44) 1223 336 033; or E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
We would like to thank the project 14-03276S of the Grant Agency of the Czech Republic
for supporting the X-ray structure analysis and the Maral Corporation for helpful assistance.
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