Uranyl Complexes with Aroylbis(N, N-dialkylthioureas)

Article abstract of DOI:10.1021/acs.inorgchem.8b01918

The reaction of isophthaloylbis(N,N-diethylthiourea), H₂L¹, with UO₂(CH₃COO)₂·2H₂O and NEt₃ as a supporting base gives a tetranuclear, anionic complex of the composition [{UO₂(L¹)}₄(OAc)₂]^2-, in which the uranyl ions are S,O-chelate bonded. Each two of them are additionally linked by an acetato ligand. Similar reactions of various uranyl starting materials (uranyl acetate, uranyl nitrate, (NBu₄)₂[UO₂Cl₄]) with corresponding pyridine-centered ligands (pyridine-2,6-dicarbonylbis(N,N-dialkylthioureas), H₂L²) yield mononuclear, neutral compounds, in which the thiourea derivatives are coordinated as S,N,N,N,S-five-dentate chelators. The equatorial coordination spheres of the formed hexagonal bipyramidal complexes [UO₂(L²)(solv)] are completed by solvent ligands (H₂O, MeOH, or DMF). Attempted reactions without a supporting base result in decomposition of the organic ligands and the formation of hexanuclear uranyl complexes with pyridine-2,6-dicarboxylato ligands, while the use of an excess of base results in condensation and the formation of dinuclear [{UO₂(L²)(μ-OMe)}₂]^2- complexes. A stable complex of the composition [UO₂(L³)] results from reactions of common uranyl starting materials with 2,2′-bipyridine-6,6′-dicarbonylbis(N,N-diethylthiourea) (H₂L³). The equatorial coordination sphere of the neutral, hexagonal bipyramidal complex is occupied by an SN₄S donor atom set, which is provided by the hexadentate organic ligand. While the uranium complexes with {L¹}^2- and {L²}^2- are labile and rapidly decompose in acidic solutions, [UO₂(L³)] is stable over a wide pH range, and the ligand readily extracts uranyl ions from aqueous solutions into organic solvents.

Full text of DOI:10.1021/acs.inorgchem.8b01918

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Uranyl Complexes with Aroylbis(N,N‑dialkylthioureas)
Christelle Njiki Noufele,† Chien Thang Pham,‡ Adelheid Hagenbach,† and Ulrich Abram*,†
†
̈
Institute of Chemistry and Biochemistry, Freie Universitat Berlin, Fabeckstrrasse 34/36, D-14195 Berlin, Germany
‡Department of Inorganic Chemistry, VNU University of Science, 19 Le Thanh Tong, Hoan Kiem, 10021 Hanoi, Vietnam
S
* Supporting Information
ABSTRACT: The reaction of isophthaloylbis(N,N-diethyl-
thiourea), H2L1, with UO2(CH3COO)2·2H2O and NEt3 as a
supporting base gives a tetranuclear, anionic complex of the
composition [{UO2(L1)}4(OAc)2]2−, in which the uranyl ions
are S,O-chelate bonded. Each two of them are additionally linked
by an acetato ligand. Similar reactions of various uranyl starting
materials (uranyl acetate, uranyl nitrate, (NBu4)2[UO2Cl4]) with
corresponding pyridine-centered ligands (pyridine-2,6-
dicarbonylbis(N,N-dialkylthioureas), H2L2) yield mononuclear,
neutral compounds, in which the thiourea derivatives are
coordinated as S,N,N,N,S-five-dentate chelators. The equatorial
coordination spheres of the formed hexagonal bipyramidal
complexes [UO2(L2)(solv)] are completed by solvent ligands
(H2O, MeOH, or DMF). Attempted reactions without a supporting base result in decomposition of the organic ligands and the
formation of hexanuclear uranyl complexes with pyridine-2,6-dicarboxylato ligands, while the use of an excess of base results in
condensation and the formation of dinuclear [{UO2(L2)(μ-OMe)}2]2− complexes. A stable complex of the composition
[UO2(L3)] results from reactions of common uranyl starting materials with 2,2′-bipyridine-6,6′-dicarbonylbis(N,N-
diethylthiourea) (H2L3). The equatorial coordination sphere of the neutral, hexagonal bipyramidal complex is occupied by
an SN4S donor atom set, which is provided by the hexadentate organic ligand. While the uranium complexes with {L1}2− and
{L2}2− are labile and rapidly decompose in acidic solutions, [UO2(L3)] is stable over a wide pH range, and the ligand readily
extracts uranyl ions from aqueous solutions into organic solvents.
uranium in the oxidation state +4 or +3.23 This includes, e.g.,
INTRODUCTION
■
chalcogenocarbamates,24,25 thiosemicarbazones,26,27 imidodi-
During the past three decades, significant progress has been
made in the molecular chemistry of the actinides. Typically,
the improvement and development of separation techniques
for actinide elements in the management and processing of the
phosphinochalcogenides, and bis(thiophosphinoyl)-
methanediides.28−35
Surprisingly, there are no reports about the coordination
chemistry of uranium with benzoylthioureas (HL0). These
nuclear fuel cycle is in the focus of interest, but also a deeper
versatile ligands form stable complexes with almost all d-block
insight into their biological distribution patterns with regard to
elements and many main group metals.36−38 They commonly
the increasing bioavailability of the elements in mining regions
is highly desirable. In recent years, the versatile coordination
chemistry particularly of the thorium and uranium has opened
a number of new fields of interest. Because uranium is
act as monoanionic S,O chelators39−49 but can also stabilize
thiophilic metal ions as neutral S-coordinated ligands.50−52
There are only two technical reports related to uranium. They
describe the functionalization of absorbent materials such as
frequently accessible in various oxidation states and has a
activated carbon or resin with benzoylthioureas for the solid-
versatile coordination chemistry, it is also interesting with
phase extraction of uranyl ions.53,54 But there is no information
regard to its general structural chemistry; catalytic, electronic,
about the chemistry involved.
and magnetic properties of their compounds; and novel
reactivity patterns.1−20
Here, we describe the formation of uranyl complexes with
the bipodal aroylthioureas H2L1, H2L2, and H2L3 (see Chart 1)
Although ligand systems combining “hard” and “soft” donor
atoms have been proven to increase and control the selectivity
as a part of a more comprehensive study about the chemistry of
uranium and thorium with such ligands.55 Such ligands have
of the complexation of metal ions, the coordination chemistry
been shown to extend the coordination abilities of acylthio-
of uranium, particularly that of uranyl compounds, is
ureas significantly. Meta-disubstituted, phenyl-centered ligands
frequently devoted to ligands with hard donor atoms. The
(e.g., H2L1) of this type form binuclear complexes, while
Cambridge Structural Database21 contains only one entry of a
uranyl compound with a uranium−phosphorus bond22 and less
than 60 with U−S bonds, while a larger variety of complexes
with soft or mixed hard/soft donor ligands is known for
Received: July 13, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Chart 1. Aroylthioureas Used Throughout This Paper
during approximately 30 min to a cold mixture of 2,2′-bipyridine-
N,N′-dioxide (11.2 g, 60 mmol) and potassium cyanide (22.5 g, 345
mmol) in 200 mL of deionized water. The reaction mixture was
stirred for 4 h, and the obtained precipitate was filtered off,
thoroughly washed with ethanol, and dried in vacuum. Yield: 70%
(8.8 g). Elemental analysis: Calcd for C12H6N4: C, 69.90; H, 2.93; N
27.17%. Found: C, 69.97; H, 2.80; N, 27.23%. IR (KBr, cm−1): 3080
(w), 2972(w), 2929(w), 2236 (m), 2010(w), 1576 (s), 1433 (s),
trinuclear assemblies are established when the chelating units
are in para-position to each other.56−60 The variation of the
central “spacer” (the phenyl ring in H2L1) increases the
flexibility of the ligand framework and its denticity. Recently,
several bimetallic complexes with the pyridine-based ligand
H2L2 have been described,61,62 while a corresponding pyrrole-
based ligand does not accommodate metal ions.63 The
bipyridine-centered, dianionic ligand {L3}2− is potentially
hexadentate and tailor-made for the formation of a
hexagonal-bipyramidal complex with a {UO2}2+ unit.64
1
1209 (w), 1156 (s), 1080 (m), 989 (s), 801 (s), 734 (m). H NMR
((CD3)2SO, ppm): 8.03−7.98 (m, 2H, bipy); 7.78 (t, 2H, J = 7.2 Hz,
bipy); 7.52−7.43 (m, 2H, bipy). 13C NMR ((CD3)2SO, ppm): 154.9
(CN); 138.7, 131.9, 128.9, 124.2, 116.6 (bipy).
2,2′-Bipyridine-6,6′-dicarboxylic Acid. 6,6′-Dicyano-2,2′-bipyri-
dine (5.5 g, 26.5 mmol) was added to a solution of NaOH (9.5 g,
238.3 mmol) in H2O/EtOH (100 mL/100 mL) and stirred at 80 °C
for 3 days. After cooling, the reaction mixture was neutralized with
conc HCl. The obtained precipitate was filtered off and washed
thoroughly with EtOH. A pure product was obtained after
recrystallization from EtOH/H2O. Yield: 80% (5.1 g). Elemental
analysis: Calcd for C12H8N2O4: C, 59.02 H, 3.30; N, 11.47%. Found:
C, 58.84; H, 3.36; N, 11.00%. IR (KBr, cm−1): 3095(w), 2982(w),
2838(w), 2555(w), 1692(vs), 1583(s), 1452(m), 1398(s), 1313(s),
EXPERIMENTAL SECTION
■
Materials. All chemicals were reagent grade and used without
further purification unless otherwise stated. (NBu4)2[UO2Cl4] was
prepared following a standard procedure from uranyl nitrate dissolved
in aqueous HCl and (NBu4)Cl. H2L1 and H2L2 were synthesized
according to the literature.62,65 THF was distilled from sodium wire
and benzophenone, and NEt3 was distilled over CaH2. All reactions
with air- and moisture-sensitive compounds were performed under an
argon atmosphere using standard Schlenk techniques unless otherwise
stated.
1
1265(m), 1172(w), 1080(m), 938(m), 824(m), 762(vs), 692(s). H
Physical Measurements. Infrared spectra were taken on a
Shimadzu FTIR spectrometer between 400 and 4000 cm−1 from KBr
pellets. NMR spectra were recorded at 300 K on a JEOL or ASC64
400 MHz multinuclear spectrometers. ESI mass spectra were
measured with an Agilent 6210 ESI-TOF mass spectrometer (Agilent
Technologies, Santa Clara, CA, United States). The solvent flow rate
was adjusted to 4 μL/min. The spray voltage was set to 4 kV, and the
drying gas flow rate to 15 psi (1 bar). All other parameters were
adjusted for a maximum abundance of the relative [M + H]+ or [M]¯
ions. Calibration salts are the source for the alkaline ions of the Na+
and K+ cluster ion peaks. All MS results are given in the form: m/z,
assignment. Because of radiation safety, not all the radioactive
compounds were measured. For a series of complexes, some
representatives were selected. Elemental analyses of carbon, hydrogen,
nitrogen, and sulfur were determined using a Heraeus Vario EL
elemental analyzer. UV/vis spectra were recorded on a SPECORD 40
instrument (Analytik Jena). The uranium contents of the samples
were measured by a HIDEX 300 SL liquid scintillation counter. An
aliquot (0.2 mL) of each sample was added to 10 mL of a scintillation
cocktail (Rotiszint ecoplus, Carl Roth), and the net count rates were
measured over 1024 channels with a counting time of 120 s.
Health Precautions. All work with radioactive material was done
in a well-ventilated cupboard in a lab approved for the handling of
uranium compounds.
NMR ((CD3)2SO, ppm): 8.74 (d, 2H, J = 7.2 Hz, bipy); 8.19−8.13
(m, 4H, bipy). 13C NMR ((CD3)2SO, ppm): 165.9 (CO); 154.4,
148.1, 139.0, 125.3, 124.2 (bipy).
2,2′-Bipyridine-6,6′-dicarbonyl Dichloride. 2,2′-Bipyridine-6,6′-
dicarboxylic acid (5 g, 20.5 mmol) was mixed with an excess of
SOCl2 (25 mL) and 2 drops of DMF and heated on reflux for 6 h.
The solvent was then removed under reduced pressure, and the
resulting colorless solid was dried under vacuum. Yield: 99% (5.7 g).
IR (KBr, cm−1): 3085 (w), 2972(w), 2929(w), 1748 (vs), 1575 (w),
1439 (w), 1242 (s), 1157 (m), 954 (m), 864 (s), 733 (s), 623 (s). 1H
NMR (CDCl3, ppm): 8.98 (dd, 2H, J1 = 1.1 Hz, J2 = 7.8 Hz, bipy);
8.18 (dd, 2H, J1 = 1.1 Hz, J2 = 7.8 Hz, bipy); 8.10 (t, 2H, J = 8.0 Hz,
bipy). 13C NMR (CDCl3, ppm): 169.7 (CO); 154.4, 149.3, 139.4,
125.3, 124.2 (bipy).
H2L3. A solution of N,N-diethylthiourea (Et2tu) (5.2 g, 40 mmol)
in 100 mL of dry THF was added dropwise to a solution of 2,2′-
bipyridine-6,6′-dicarbonyl dichloride (5.6 g, 20 mmol) in 100 mL of
dry THF at room temperature. After being stirred for 1 h, dry
triethylamine (4.2 mL, 30 mmol) was added, and the reaction mixture
was stirred at 50 °C for an additional 45 min. The formed colorless
precipitate (HNEt3Cl) was filtered off, and the remaining solvent was
removed under reduced pressure. The yellow product was recrystal-
lized from methanol/chloroform (5:1). Yield: 65% (6.3 g). Elemental
analysis: Calcd for C22H28N6O2S2: C, 55.91; H, 5.97; N, 17.78; S,
13.57%. Found: C, 55.92; H, 5.97; N, 17.72; S, 13.59%. IR (KBr,
cm−1): 3375(m), 3318(m), 3190(m), 3082(w), 2972(m), 2929(w),
1707(vs), 1627(m), 1581(m), 1521(s), 1467(w), 1419(s), 1363(m),
Synthesis of H2L3. 6,6′-Dicyano-2,2′-bipyridine. The compound
was synthesized according to the method outlined by Sharmoukh and
Allam with some modifications.66 A solution of benzoyl chloride (24
mL, 208 mmol) in 80 mL of dichloromethane was added dropwise
B
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1280(m), 1219(m), 1126(m), 1074(m), 1014(w), 931(w), 861(w),
756(m), 667(w). H NMR (CDCl3, ppm): 10.21 (s, 2H, NH); 8.54
998(m), 943(m), 922(s), 862(s), 764(s), 682(m). UV/vis (CH2Cl2,
nm): 230 (ε = 3.2 × 103 L mol−1cm−1), 260 (ε = 4.4 × 103 L mol−1
cm−1), 368 (ε = 0.4 × 103 L mol−1 cm−1).
1
(dd, 2H, J1 = 1.2 Hz, J2 = 8.0 Hz, bipy); 8.26 (dd, 2H, J1 = 1.1 Hz, J2 =
8.0 Hz, bipy), 8.08 (t, 2H, J = 8.0 Hz, bipy): 4.06−4.04 (m, 4H,
CH2); 3.71−3.68 (m, 4H, CH2); 1.37−1.20 (m, 12H, CH3). 13C
NMR (CDCl3, ppm): 178.6 (CS); 159.8 (CO); 153.8, 148.1,
139.1, 124.7, 123.9 (bipy); 47.9, 45.6, (CH2); 13.5, 12.5 (CH3). ESI+
MS (m/z): 511.1364 (calcd. 511.1352) [M+K]+; 495.1625 (calcd.
495.1613) [M + Na]+; 473.1806 (calcd. 473.1793) [M + H]+. UV/vis
(CH2Cl2, nm): 218 (ε = 43.6 × 103 L mol−1cm−1), 246 (ε = 59.5 ×
103 L mol−1 cm−1), 280 (ε = 49.1 × 103 L mol−1cm−1), 354 (ε = 3.5
× 103 L mol−1cm−1).
[UO2(L2a)(MeOH)]. H2L2a (39.5 mg, 0.1 mmol) was dissolved in
MeOH (3 mL) and added to a stirred solution of (NBu4)2[UO2Cl4]
(90 mg, 0.1 mmol) or UO2(CH3COO)2·2H2O (42.4 mg, 0.1 mmol)
in MeOH (3 mL). Two drops of NEt3 were added, and the reaction
mixture was stirred for 1 h. Single crystals for X-ray diffraction were
obtained after slow evaporation of the mother solution at room
temperature. Yield: 70% (48 mg). Elemental analysis: Calcd for
C18H27N5O5S2U: C, 31.08; H, 3.91; N, 10.07; S, 9.22%. Found: C,
31.09; H, 3.90; N, 10.05; S, 9.21%. IR (KBr, cm−1): 3211(w),
2972(w), 2935(w), 2873(w), 1654(vs), 1591(s), 1523(s), 1429(s),
1396(s), 1348(m), 1313(w), 1263(m), 1205(w), 1151(m), 1078(m),
1016(m), 945(m), 912 (vs), 850(m), 763(m), 680(w). 1H NMR
((CD3)2SO, ppm): 8.51 (d, 2H, J = 8.4 Hz, py); 8.43 (t, 1H, J = 8.4
Hz, py); 3.97−3.91 (m, 4H, CH2); 3.55−3.50 (m, 4H, CH2); 1.24 (t,
6H, J = 7.0 Hz, CH3); 1.01 (t, 6H, J = 7.0 Hz, CH3). 13C NMR
((CD3)2SO, ppm): 191.3 (CS); 174.8 (CO); 142.4, 139.6, 125.9
(py); 45.1, 46.1 (CH2); 12.3, 13.5 (CH3). ESI+ MS (m/z):
1365.3036 (calcd. 1365.3036) [{2M−MeOH}+K]+; 702.1331
(calcd. 702.1336) [{M−MeOH}+K]+. UV/vis (CH2Cl2, nm): 232
(ε = 4.1 × 103 L mol−1cm−1), 281 (ε = 3.3 × 103 L mol−1cm−1), 397
(ε = 0.4 × 103 L mol−1cm−1).
Syntheses of the Complexes. (NBu4)2[{UO2(L1)}4(OEt)2(HOEt)2].
H2L1 (39.4 mg, 0.1 mmol) was dissolved in EtOH (3 mL) and added
to a stirred solution of (NBu4)2[UO2Cl4] (90 mg, 0.1 mmol) in EtOH
(3 mL). After 10 min, 3 drops of NEt3 were added, and the reaction
mixture was stirred at room temperature for 1 h. The orange-red
precipitate was collected by filtration, washed with EtOH, and dried in
vacuum. Single crystals for X-ray diffraction were obtained after slow
evaporation of a CH2Cl2/EtOH 1:1 (v/v) solution at room
temperature. Yield: 40% (33 mg). Elemental analysis: Calcd for
C112H190N18O20S8U4: C, 40.55; H, 5.77; N, 7.60; S, 7.73%. Found: C,
40.54; H, 5.59 N, 7.88; S, 8.25%. IR (KBr, cm−1): 3446 (m), 2966
(m), 2931 (m), 2873 (w), 1595 (w), 1500 (vs), 1423 (s), 1394 (s),
1309 (w), 1251 (w), 1140 (m), 1078 (m), 910 (s), 825 (m), 729 (m),
[UO2(L2a)(DMF)]. Yellow needles of the compound were synthe-
sized by dissolving [UO2(L2a)(MeOH)] (35 mg, 0.05 mmol) in DMF
(1 mL) and slow evaporation of the solvent at room temperature.
Yield: 90% (36 mg). Elemental analysis: Calcd for C23H37N7O6S2U
([UO2(L2a)(DMF)]·DMF): C, 34.12 H, 4.61; N, 12.11; S, 7.92%.
Found: C, 34.11; H, 4.61; N, 12.10; S, 7.89%. IR (KBr, cm−1):
3429(w), 2972(w), 2933(w), 2872(w), 1668(w), 1629(vs), 1593(w),
1517(m), 1429(m), 1373(s), 1317(w), 1286(w), 1259(m), 1205(w),
1149(m), 1091(m), 1014(m), 948(m), 904(vs), 842(m), 761(m),
677(w), 653(w), 638(w). 1H NMR ((CD3)2SO, ppm): 8.48 (d, 2H, J
= 8.0 Hz, py); 8.40 (t, 1H, J = 8.0 Hz, py); 7.86 (s, 2H, CH_DMF);
3.97−3.91 (m, 4H, CH2); 3.55−3.49 (m, 4H, CH2); 2.83 (s, 12H,
CH3_DMF); 1.23 (t, 6H, J = 7.0 Hz, CH3); 1.00 (t, 6H, J = 7.0 Hz,
CH3). 13C NMR ((CD3)2SO, ppm): 191.4 (CS); 163.2 (C
O_DMF); 158.4 (CO); 121.5, 125.9, 142.4 (py); 45.1, 46.1,
(CH2); 31.3, 36.3 (CH3_DMF); 12.2, 13.4 (CH3). ESI+ MS (m/z):
2012.4997 (calcd. 2012.4996) [3{M−DMF}+Na]; 1349.3322 (calcd.
1349.3296) [2{M−DMF}+Na]; 686.1625 (calcd. 686.1597) [{M−
DMF}+Na].
1
669 (w). H NMR (CD2Cl2, ppm): 11.30 (s, 2H, OH_EtOH); 8.43
(m, 4H, Ph), 8.34 (d, 8H, J = 7.6 Hz, Ph), 7.49 (m, 4H, Ph); 4.26−
4.05 (m, 32H, CH2); 2.55−2.41 (m, 24H, CH2_NBu4, CH2_EtOH),
1.48−1.24 (m, 32H, CH2_NBu4); 1.01−0.92 (m, 48H, CH3); 0.82 (t,
12H, J = 7.1 Hz, CH3_EtOH); 0.65−0.61 (m, 18H, CH3_NBu4). 13
C
NMR (CD2Cl2, ppm): 184.2 (CS); 173.3 (CO); 137.2, 132.9,
131.1, 127.6 (Ph); 57.8 (CH2_EtOH); 47.6, 46.3 (CH2); 45.9
(CH2_NBu4); 23.2 (CH2_NBu4); 19.2 (CH2_NBu4); 13.2
(CH3_EtOH); 13.4, 12.3 (CH3); 8.9 (CH3_NBu4). UV/vis
(CH2Cl2, nm): 232 (ε = 12.5 × 103 L mol−1cm−1), 283 (ε = 11.5
× 103 L mol−1cm−1), 368 (ε = 1.8 × 103 L mol−1cm−1).
(HNEt3)2[{UO2(L1)}4(OAc)2]. H2L1 (39.4 mg, 0.1 mmol) was
dissolved in EtOH (3 mL) and added to a stirred solution of
UO2(CH3COO)2·2H2O (42.4 mg, 0.1 mmol) in EtOH (3 mL). After
10 min, 3 drops of NEt3 were added, and the reaction mixture was
stirred at room temperature for 1 h. The orange-red precipitate was
collected by filtration, washed with MeOH, and dried in vacuum.
Single crystals for X-ray diffraction were obtained after slow
evaporation of a CH2Cl2/MeOH 1:1 (v/v) solution at room
temperature. Yield: 68% (52 mg). Elemental analysis: Calcd for
C90H138Cl4N18O20S8U4 ((HNEt3)2[{UO2(L1)}4(OAc)2]·2CH2Cl2):
C, 34.40; H, 4.43; N, 8.02; S, 8.16%. Found: C, 34.42; H, 4.40; N,
8.01; S, 8.27%. IR (KBr, cm−1): 3062(w), 2976 (w), 2931 (w), 2872
(w), 1680 (w), 1587 (w), 1500 (vs), 1426 (s), 1382 (s), 1311 (w),
1251 (w), 1138 (m), 1078 (m), 1010 (w), 910 (s), 827 (m), 729 (m),
653 (w). 1H NMR (CDCl3, ppm): 10.23 (s, 4H, Ph), 8.44 (dd, 8H, J1
= 8.0 Hz, J2 = 2.0 Hz, Ph), 7.46 (t, 4H, J = 8.0 Hz, Ph); 4.35−3.74
(m, 32H, CH2); 3.00 (s, 6H, CH3_OAc); 2.26 (m, 6H,
CH2_HNEt3), 1.37−1.08 (m, 48H, CH3); 0.63 (t, 18H, J = 7.7 Hz,
CH3_HNEt3). 13C NMR (CDCl3, ppm): 184.8 (CS); 173.1 (C
O_OAc); 170.4 (CO); 137.2, 132.8, 131.6, 127.8 (Ph); 47.7, 46.1
(CH2); 45.6 (CH2_HNEt3); 25.6 (CH3_OAc); 13.6, 12.6 (CH3); 8.4
[UO2(L2b)(OH2)]. H2L2b (42.3 mg, 0.1 mmol) was dissolved in
MeOH (3 mL) and added to a stirred solution of (NBu4)2[UO2Cl4]
(90 mg, 0.1 mmol) or UO2(CH3COO)2·2H2O (42.4 mg, 0.1 mmol)
in MeOH (3 mL). After 10 min, 2 drops of NEt3 were added and the
reaction mixture was stirred for 1 h. The light-yellow precipitate was
collected by filtration, washed with MeOH, and dried in vacuum.
Single crystals for X-ray diffraction were obtained after slow
evaporation of a CH2Cl2/MeOH 1:1 (v/v) solution at room
temperature. Yield: 60% (42 mg). Elemental analysis: Calcd for
C17H21N5O7S2U: C, 28.78; H, 2.98; N, 9.87; S, 9.04%. Found: C,
28.78 H, 2.98; N, 9.89; S, 9.04%. IR (KBr, cm−1): 3229(m), 2972(w),
2920(w), 2854(w), 1606(vs), 1516(s),1429(m), 1386(s), 1298(m),
1236(w), 1105(m), 1024(m), 912 (vs), 846(m), 766(w), 698(w),
1
551(w). H NMR ((CD3)2SO, ppm): 8.50 (d, 2H, J = 6.8 Hz, py);
(CH3_HNEt3). UV/vis (CH2Cl2, nm): 232 (ε = 12.5 × 103
L
8.44 (t, 1H, J = 6.8 Hz, py); 3.81−3.51 (m, 16H, CH2). 13C NMR
((CD3)2SO, ppm): 192.1 (C = S); 162.8 (CO); 158.2, 142.4, 126.1
(py); 66.4 (CH2−O); 46.2 (CH2−N). ESI+ MS (m/z): 2096.3828
(calcd. 2096.3751) [{M−H2O}3+Na]+; 1405.2538 (calcd.
1405.2467) [2{M−H2O}+Na]+; 730.0963 (calcd. 730.0922) [{M−
H2O}+K]+; 714.1232 (calcd. 714.1182) [{M−H2O}+Na]+. UV/vis
(CH2Cl2, nm): 230 (ε = 3.4 × 103 L mol−1cm−1), 269 (ε = 2.6 × 103
L mol−1cm−1), 370 (ε = 0.4 × 103 L mol−1cm−1).
mol−1cm−1), 283 (ε = 11.5 × 103 L mol−1cm−1), 368 (ε = 1.8 × 103 L
mol−1cm−1).
[UO2(dipicolinate)(H2O)]6. H2L2a (39.5 mg, 0.1 mmol) was
dissolved in MeOH (3 mL) and added to a stirred solution of
(NBu4)2[UO2Cl4] (90 mg, 0.1 mmol) or UO2(CH3COO)2·2H2O
(42.4 mg, 0.1 mmol) or UO2(NO3)2·6H2O (50.2 mg, 0.1 mmol) in
MeOH (3 mL), and the reaction mixture was stirred for 1 h. Single
crystals for X-ray diffraction were obtained after slow evaporation of
the mother solution at room temperature. Yield: 60% (27 mg). IR
(KBr, cm−1): 3267(s), 3070(w), 2972(m), 2934(m), 2874(w),
1628(vs), 1522(vs), 1470(vs), 1445(vs), 1417(vs), 1377(m),
1343(w), 1274(m), 1225(s), 1169(m), 1130(m), 1101(m),
[UO2(L2b)(DMF)]. The compound was synthesized by dissolving
[UO2(L2b)(OH2)] (35 mg, 0.05 mmol) in DMF (1 mL) and slow
evaporation of the solvent at room temperature. Yield: 92% (35 mg).
Elemental analysis: Calcd for C20H26N6O7S2U: C, 31.42; H, 3.43; N,
10.99; S, 8.39%. Found: C, 31.40; H, 3.44; N, 10.99; S, 8.37%. IR
C
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(KBr, cm−1): 3446(w), 2960(w), 2924(w), 2856(w), 1631(s),
1595(w), 1500(vs),1423(m), 1371(s), 1298(m), 1232(w),
1111(m), 1066(w), 1033(m), 908 (vs), 844(m), 759(w), 677(w),
634(w), 607(w), 553(w), 505(w). 1H NMR ((CD3)2SO, ppm): 8.50
(d, J = 7.0 Hz, 2H, py), 8.45 (t, J = 7.0 Hz, 1H, py), 7.86 (s, 1H,
CH_DMF), 3.88−3.55 (m, 16H, CH2), 2.86 (s, 6H, CH3_DMF).
13C NMR ((CD3)2SO, ppm): 192.1 (CS), 164.5 (CO_DMF),
159.7 (CO), 148.6, 133.2, 126.1 (py), 66.7 (CH2−O), 46.2 (CH2−
N), 36.3, 31.5 (CH3_DMF). ESI+ MS (m/z): 1405.2505 (calcd.
1405.2467) [{M−DMF}2+Na]+; 730.1010 (calcd. 730.0922) [{M−
DMF+K]+; 714.1219 (calcd. 714.1182) [{M−DMF}+Na]+; 692.1401
(calcd. 692.1363) [{M−DMF+H]+.
182.0 (CS), 161.6 (CO), 156.8, 155.9, 143.2, 127.3, 127.0
(bipy), 47.1, 46.1, (CH2), 12.9, 12.8 (CH3). ESI+ MS (m/z):
779.1550 (calcd. 779.1602) [M+K]+; 763.1816 (calcd. 763.1862) [M
+ Na]+; 741.1991 (calcd. 741.2043) [M + H]+. UV/vis (CH2Cl2,
nm): 230 (ε = 2.4 × 103 L mol−1cm−1), 260 (ε = 2.2 × 103 L
mol−1cm−1), 305 (ε = 1.7 × 103 L mol−1cm−1).
Stability Tests. The complexes (HNEt3)2[{UO2(L1)}4(OAc)2],
[UO2(L2a)(MeOH)], [UO2(L2b)(H2O)], and [UO2(L3)] were used
for the two-phase extraction experiments. They were performed at
room temperature in microcentrifuge tubes (5 mL) with a phase ratio
V(org):V(aq) of 2:2 mL. The pH of the aqueous phase was adjusted with
nitric acid, and a constant ionic strength was maintained by the
addition of (NEt4)NO3 (0.5 mM). The organic phase (0.4 mM) was
prepared by dissolving the complexes in CH2Cl2. The samples were
shaken for 30 min. The aqueous phase was separated from the organic
one, and the depletion of the uranyl ions was monitored in suitable
aliquots (usually 200 μL), measuring the concentration of the uranyl
ions radiometrically using a liquid scintillation counter. The remaining
organic phase was analyzed by UV/vis spectroscopy.
Computational Details. DFT (density functional theory)
calculations were performed with the high-performance computing
system of the ZEDAT (SOROBAN)67 using the program packages
GAUSSIAN 09 and GAUSSIAN 16.68,69 The gas phase geometry
optimizations were performed using coordinates derived from the X-
ray crystal structures or by modification of the structures using
GAUSSVIEW. The calculations for the ligand molecules H2L1, H2L2a,
and H2L2b were performed without any restrictions on the structures
by using the hybrid density functional B3LYP together with the
standard basis set 6-311G for all atoms.70−72 For molecules
containing uranium, the calculations were also performed without
any restrictions on the structures by using the hybrid density
functional B3LYP,70−72 together with the basis sets obtained from the
EMSL database 6-311++G for all atoms excluding uranium. For
uranium, the pseudopotential LANL2DZ was used.73,74
X-ray Crystallography. The intensities for the X-ray determi-
nations were collected on STOE IPDS 2T or Bruker D8 Venture
instruments with Mo Kα or Cu Kα radiation. The space groups were
determined by the detection of systematical absences. Absorption
corrections were carried out by SADABS or X-RED32.75−77 Structure
solutions were performed with the programs SHELXS 86, SHELXS
97, and SHELXS 2014; structure refinements were done with the
SHELXL 2014 program.78,79 Hydrogen atoms were placed at
calculated positions and treated with the “riding model” option of
SHELXL. For [UO2(L2a)(MeOH)] and [UO2L2b(H2O)], the hydro-
gen atoms of the solvent molecules (methanol and water) were
located on the basis of the electron density of the Fourier map and
refined. Details about the measurement and refinement data are
summarized in the Supporting Information. The structures of the
representation of molecular structures was done using the programs
DIAMOND 4.2.2.80 Because ball and stick presentations of the
molecules are used in most of the figures of this paper for reasons of
clarity, ellipsoid representations of all compounds are contained in the
Supporting Information.
(HNEt3)2[{UO2(L2a)(μ2-OMe)}2]. (a) [UO2(L2a)(MeOH)] (69.5 mg,
0.1 mmol) was dissolved in 5 mL of warm methanol and NEt3 (2
drops) was added. Orange-yellow crystals precipitated after cooling
and partial evaporation of the solvent. Yield: 80% (64 mg). (b) H2L2a
(19.8 mg, 0.05 mmol) was dissolved in MeOH (3 mL) and added to a
stirred solution of (NBu4)2[UO2Cl4] (90 mg, 0.1 mmol) or
UO2(CH3COO)2·2H2O (42.4 mg, 0.1 mmol) in MeOH (3 mL).
Two drops of NEt3 were added, and the reaction mixture was stirred
for 1 h. The obtained precipitate was filtered off, washed with MeOH,
and dried under vacuum. Single crystals for X-ray diffraction were
obtained after slow evaporation of a CH2Cl2/MeOH 1:2 (v/v)
solution at room temperature. Yield: 74% (59 mg).
Elemental analysis: Calcd for C48H84N12O10S4U2: C, 35.76; H,
5.17; N, 10.65; S, 8.12%. Found: C, 35.55; H, 5.27; N, 10.41; S,
8.10%. IR (KBr, cm−1): 3429(m), 3070(w), 2974(m), 2933(w),
2874(w), 2681(w), 1589 (vs), 1497(m), 1462(w), 1425(m), 1382(s),
1309(m), 1278(m), 1247(s), 1201(w), 1145(m), 1120(m), 1070(m),
1016(m), 950(w), 912 (vs), 868(w), 766(s), 678(w), 638(m). UV/
vis (CH2Cl2, nm): 230 (ε = 8.3 × 103 L mol−1cm−1), 265 (ε = 7.8 ×
103 L mol−1cm−1), 304 (ε = 4.9 × 103 L mol−1cm−1), 368 (ε = 1.2 ×
103 L mol−1cm−1).
(HNEt3)2[{UO2(L2b)(μ2-OMe)}2]. (a) [UO2(L2a)(OH)2] (71, mg, 0.1
mmol) was dissolved in 5 mL of warm methanol and NEt3 (2 drops)
was added. Yellow crystals deposited after cooling and partial
evaporation of the solvent. Yield: 71 mg (58 mg). (b) H2L2b (84.6
mg, 0.2 mmol) was dissolved in MeOH (3 mL) and added to a stirred
solution of (NBu4)2[UO2Cl4] (90 mg, 0.1 mmol) or
UO2(CH3COO)2·2H2O (42.4 mg, 0.1 mmol) in MeOH (3 mL).
Two drops of NEt3 were added, and the reaction mixture was stirred
for 1 h. The obtained precipitate was filtered off, washed with MeOH,
and dried under vacuum. Single crystals for X-ray diffraction were
obtained after slow evaporation of a CH2Cl2/MeOH 1:1 (v/v)
solution at room temperature. Yield: 77% (76 mg).
Elemental analysis: Calcd for C48H76N12O14S4U2: C, 34.95; H,
4.64; N, 10.19; S, 7.77%. Found: C, 35.17; H, 5.09; N, 9.53; S, 7.62%.
IR (KBr, cm−1): 3428(w), 2976(w), 2922(w), 2855(w), 2683(w),
1587(vs), 1475(m), 1427(s), 1381(m), 1280(s), 1229(m), 1111(m),
1064(w), 1026(m), 951(m), 901 (s), 841(m), 777(m), 760(m),
702(w), 629(m). UV/vis (CH2Cl2, nm): 230 (ε = 3.4 × 103
L
mol−1cm−1), 269 (ε = 2.6 × 103 L mol−1cm−1), 370 (ε = 0.4 × 103 L
mol−1cm−1).
The structure measurements of (NBu4)2[{UO2(L1)}4(OEt)2-
(HOEt)2 are not of sufficient quality to justify a detailed discussion
of bond lengths and angles or the deposit in the crystallographic
database. For this reason, they are not included in the crystallographic
material. But, they doubtlessly confirm the structures of the
compounds and are used as such in the following discussion.
Additional information on the structure determinations is contained
in the Supporting Information and has been deposited with the
Cambridge Crystallographic Data Centre.
[UO2(L3)]. H2L3 (42.3 mg, 0.1 mmol) was dissolved in MeOH (3
mL) and added to a stirred solution of (NBu4)2[UO2Cl4] (90 mg, 0.1
mmol) or UO2(CH3COO)2·2H2O (42.4 mg, 0.1 mmol) in MeOH (3
mL). Two drops of NEt3 were added, and the reaction mixture was
stirred for 1 h. The light-yellow precipitate was collected by filtration,
washed with MeOH, and dried under vacuum. Single crystals for X-
ray diffraction were obtained after slow evaporation of a CH2Cl2/
MeOH 1:1 (v/v) solution at room temperature. Yield: 90% (67 mg).
Elemental analysis: Calcd for C22H26N6O4S2U: C, 35.68; H, 3.54; N,
11.35 S, 8.66%. Found: C, 35.67; H, 3.61; N, 11.36; S, 8.63%. IR
(KBr, cm−1): 2972(w), 2937(w), 2873(w), 1637(vs), 1598(m),
1517(vs), 1458(m), 1409(m), 1371(s), 1330(w), 1284(w), 1244(m),
1149(m), 1087(m), 1014(m), 908(vs), 819(m), 761(m), 671(w). 1H
NMR ((CD3)2SO, ppm): 9.13 (d, 2H, J = 8.0 Hz, bipy), 8.68 (t, 1H, J
= 8.0 Hz, bipy), 8.61 (d, 2H, J = 8.0 Hz, bipy), 4.13−4.08 (m, 4H,
CH2), 3.84−3.79 (m, 4H, CH2), 1.40−1.36 (t, 6H, J = 7.3 Hz, CH3),
1.23−1.19 (t, 6H, J = 7.3 Hz, CH3). 13C NMR ((CD3)2SO, ppm):
RESULTS AND DISCUSSION
■
The synthesis of the bipodal isophthaloylbis(N,N-diethyl-
thiourea), H2L1, was done in a one-pot reaction from
isophtaloyl chloride, (NH4)SCN, and diethylamine as has
been reported by Koch et al.56 Such an approach works
perfectly for the phenyl-centered ligand but cannot be applied
D
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Synthesis of H2L2
Scheme 2. Synthesis of H2L3
Figure 1. Molecular structure of H2L3.
for the ligands H2L2 and H2L3, which possess pyridine
functionalities. They require a presynthesis of N,N-dialkylth-
ioureas,81 which can then be coupled to the appropriate
carboxylic acid chloride (Scheme 1).62 The use of THF instead
of acetone as solvent for such reactions improves the yields to
up to 90% because H2L2a and H2L2b are slightly soluble in
acetone. The morpholine-derivative H2L2b was added to this
work because the additional oxygen donor atoms may generate
interesting inter- or intramolecular interactions, as has been
shown in a previous work.61
protons. The resonances of the aromatic protons are observed
at 8.56, 8.26, and 8.08 ppm. The hindered rotation around the
C(S)-NEt2 bond, which is found in many benzoylthioureas,49
is also observed in H2L3. This results in a magnetic
inequivalence of the two diethyl residues. Two multiplets at
4.04 and 3.68 ppm for the CH2 protons and one multiplet at
1.20 ppm for the CH3 protons are observed. The composition
of the ligand is also confirmed by its ESI+ mass spectrum with
the molecular ion [M + H]+ peak at m/z = 473.1806.
Single crystals of H2L3 were obtained after recrystallization
from a CH2Cl2/diethyl ether (1:5) mixture. Figure 1 shows the
molecular structure of the compound. Only half of the
molecule is contained in the asymmetric unit. The complete
ligand is produced by an inversion center being located
between C25 and C25′. The C−O bond length of 1.214(2) Å
and the C−S bond length of 1.673(2) Å are within the
expected ranges of corresponding double bonds. The C2−N3
and C4−N3 bond lengths are 1.406(2) and 1.380(2) Å,
respectively, and reflect a partial double bond character,
suggesting a delocalization of π-electron density. Similarities
with these observed values were previously reported for other
bipodal aroylthioureas.63,82 More bond lengths and angles are
given in the Supporting Information.
For the synthesis of 2,2′-bipyridine-6,6′-dicarbonylbis(N,N-
diethylthiourea), the dichloride of 2,2′-bipyridine-6,6′-dicar-
boxylic acid was synthesized prior to the coupling reaction with
Et2tu (N,N-diethythiourea) as is shown in Scheme 2. First, 2,2-
bipyridine is converted into 2,2′-bipyridine-N,N′-dioxide,
followed by its functionalization with a cyanide groups. The
resulting 6,6′-dicyano-2,2′-bipyridine is then hydrolyzed, and
the dicarboxylic acid is obtained as a colorless precipitate with
a final yield of about 50%. It is converted into the
corresponding dichloride by heating with an excess of thionyl
chloride. H2L3 is obtained from the reaction of the dichloride
with two equivalents of Et2tu in the presence of triethylamine.
The colorless product is soluble in solvents such as THF,
acetone, CH2Cl2, or CHCl3. The IR spectrum of H2L3 shows a
band at 3375 cm−1, which corresponds to the N−H stretch.
The strong absorption band at 1707 cm−1 can be assigned to
The three bipodal thiourea ligands H2L1, H2L2 and H2L3
were reacted with common uranyl starting materials such as
UO2(CH3COO)2·2H2O or (NBu4)2[UO2Cl4]. In some cases
(particularly when the acidic (NBu4)2[UO2Cl4] was used), the
addition of NEt3 as a supporting base was required to
1
the CO vibration. The H NMR spectrum in CDCl3 is
characterized by a singlet at 10.21 ppm belonging to the N−H
E
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 3. Reactions of Uranyl Salts with the Bipodal Aroylthioureas under Study and Their Products
Figure 2. Structure of the [{UO2(L1)}4(OAc)2]2− anion.
deprotonate the organic ligands and avoid decomposition of
the ligands. A summary of the performed reactions and the
obtained products is given in Scheme 3.
spectrum of the compound, where no signals for the N−H
protons are observed. A tetranuclear structure of the
compound was confirmed by X-ray diffraction. The compound
Treatment of UO2(CH3COO)2·2H2O with an equivalent
amount of H2L1 in EtOH at room temperature gave an orange-
red solution, from which a solid precipitated after the addition
of two drops of NEt3. Yellow crystals of (HNEt3)2[{UO2-
(L1)}4(μ2-OAc)2]·CH2Cl2 were obtained after recrystallization
from CH2Cl2/EtOH. The IR spectrum of the complex shows
the νUO band at 910 cm−1. A weak band at 1680 cm−1 can be
assigned as the νCO stretch of the acetato bridges. The νCO
stretching frequency of the organic ligand appears in the
complex at 1500 cm−1. A bathochromic shift of 180 cm−1 is
observed in comparison to the position of this band in the
uncoordinated H2L1. This indicates a chelate formation with a
strong degree of electron delocalization. Such strong bath-
ochromic shifts of the carbonyl frequencies have also been
observed in benzoyl(N,N-dialkylthioureato) complexes with
other metal ions.37,38,57,59 The absence of a band above 3000
cm−1 indicates the deprotonation of the ligands during the
complex formation, which is confirmed by the 1H NMR
̅
crystallizes in the triclinic space group P1 with an asymmetric
unit, which contains half of a complex molecule, one
triethylammonium cation, and a half dichloromethane
molecule. Figure 2 shows the structure of the
[{UO2(L1)}4(OAc)2]2− anion.
The tetranuclear complex contains four uranyl units, four
deprotonated {L1}2− ligands, and two acetato ligands. Each
uranyl moiety is coordinated equatorially by two S,O-bonded
aroylthiourea units coming from two different ligands. This is a
relatively rare coordination mode for uranyl ions, and a similar
S,O chelate formation has hitherto been observed only for
some complexes with monothiocarbamates,83−85 heterocyclic
thionates,86,87 or substituted phosphine sulfides.88 The high
flexibility of the isophthaloylbis(thiourea) ligand allows the
coordination of the equatorial coordination spheres of the
uranyl cations in the present structure.
The coordination environments of the uranium atoms are
pentagonal-bipyramids resulting from the cis S,O-coordination
F
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 1. Selected Bond Lengths (Å), Distances (Å), and Bond Angles (deg) in (HNEt3)2[{UO2(L1)}4(OAc)2]
distances
U1−O1
U1−O2
U1−S1
U1−S21
U1−O5
U1−O25
U1−O71
C2−S1
1.776(9)
1.788(9)
2.844(4)
2.841(4)
2.275(8)
2.339(8)
2.402(8)
1.70(1)
C4−O5
1.27(2)
1.71(2)
1.36(2)
1.28(2)
1.26(2)
1.76(1)
1.78(1)
2.847(4)
2.844(8)
2.286(8)
U2−O35
U2−O72
C12−N13
N13−C14
C14−O15
C32−N33
N33−C34
C34−O35
U1···U2
2.336(8)
C22−S21
C22−N23
N23−C24
C24−O25
U2−O11
U2−O12
U2−S11
U2−S31
U2−O15
2.415(8)
1.36(2)
1.28(2)
1.26(2)
1.36(2)
1.28(2)
1.26(2)
6.85(1)
C2−N3
N3−C4
1.38(2)
1.31(2)
U1···U2′
11.74(1)
angles
O1−U1−O2
O1−U1−O5
O1−U1−O71
O11−U2−O12
178.5(4)
90.8(4)
92.9(4)
O1−U1−O25
O2−U1−O25
O2−U1−O5
88.9(4)
90.8(3)
90.8(4)
O1−U1−S1
O2−U1−S1
O1−U1−S21
90.3(4)
90.9(4)
88.7(7)
177.3(5)
a
Symmetry operator: (′) −x+1,−y+1,−z+1.
of two deprotonated {L1}2− ligands and an additional acetato
ligand. Selected bond lengths and angles are listed in Table 1.
The uranyl bond lengths are between 1.776(1) and 1.788(9)
Å, which is unexceptional and in line with published values.21
The O−U−O angles are 178.5(4) and 177.3(5)°. Two
conformation types of the ligand are established in the
[{UO2(L1)}4(OAc)2]2− anion: the linear conformation A and
the hitherto unprecedented conformation B (Chart 2). The
Chart 2. Two Relevant Conformations of H2L1
Figure 3. (a) Chelate rings in the [{UO2(L1)}4(OAc)2]2− anion and
(b) visualization of the π−π interactions.
bond lengths between the uranium atoms and the oxygen
donor atoms of the organic ligand with the conformation A are
around 2.28(1) Å and slightly shorter than the U−O bond
lengths to the ligand with the conformation B with
approximately 2.34(1) Å. The U−S bonds are almost equal
with approximately 2.84 Å. The S,O chelate rings exhibit the
typical extended delocalized π-systems with a slight elongation
of the C−O and C−S bonds and a shortening of the C−N
bonds, reflecting some double bond character.
To quantify the formation of two conformers of the organic
ligand, DFT calculations on different conformations of H2L1
were performed (for details, see Supporting Information).
They confirm conformation A as the most stable conformation
with an energy difference of 28 kJ/mol to the conformation B.
Such a small difference in energy does not prevent the
formation of metal complexes with the other conformations
but may explain the preference of A in most of the hitherto
known compounds, where no additional intramolecular
interactions play a role. This is slightly different in the
[{UO2(L1)}4(OAc)2]2− anion, for which two interesting
features are briefly discussed. As is illustrated in Figure 3a,
the S,O chelate rings belonging to the conformation B strongly
deviate from planarity (rms: 0.3556, maximum deviation for
0.543(7) Å for S21), while the S,O chelates resulting from the
ligand with conformation A are planar with a maximum
deviation of 0.210(9) Å for O5 (rms: 0.139). The latter values
are in agreement with the situation in the chelate rings of other
transition metal complexes with aroylthiourea ligands.36−49
Surprisingly, the distortions do not significantly influence the
bond lengths inside the chelate rings and the previously
mentioned C−N bond length equalization, but they allow
additional weak attractive intramolecular π−π interactions via
the central phenyl rings. The two rings are coplanar, and the
C53−C53′ distance is 3.31(3) Å (see Figure 3b).
Each two uranium atoms in the [{UO2(L1)}4(OAc)2]2−
anion are linked by an acetato bridge. Their oxygen atoms
occupy the fifth positions of the pentagonal bipyramidal
coordination spheres of the metal atoms. The established
bridge, however, is obviously not mandatory for the
stabilization of the tetrameric complex. The reaction of
(NBu4)2[UO2Cl4] with H2L1 in EtOH gives a similar product
but with EtO−/EtOH ligands instead of acetate ligands (see
Scheme 3). The obtained orange-red precipitate has a
composition of (NBu4)2[{UO2(L1)}4(OEt)2(HOEt)2]. The
IR spectrum of the product shows a broad signal at 3446 cm−1,
which can be assigned to O−H vibrations. The absence of a
vibration at 3100 cm−1 indicates the deprotonation of H2L1.
G
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 4. Molecular structure of the [{UO2(L1)}4(OEt)2(HOEt)2]2− anion.
Chart 3. Selected Conformations of H2L2a with Energy Differences between the Conformers
The formation of a uranyl complex is confirmed by the
presence of the strong band at 910 cm−1. As in
(HNEt3)2[{UO2(L1)}4(OAc)2], a bathochromic shift of the
νCO stretch is observed. The presence of two (O−H) protons
At first, reactions of H2L2a and H2L2b with uranyl nitrate
hexahydrate or uranyl acetate dihydrate were performed in
MeOH at 50 °C without the addition of a supporting base.
Such reactions ended in a decomposition of the ligands and the
formation of dipicolinic acid. This hydrolysis product finally
forms a hexanuclear uranyl complex of the composition
[UO2(dipicolinate)(H2O)]6 (see Scheme 3), which has
already been described by Immirizi et al.89 Obviously, the
thiourea derivatives are sensitive against the strong acidic
conditions in such solutions. Similar observations were made
by Gatto during the reaction of a monosubstituted
diacetylresorcinol thiosemicarbazone ligand and uranyl ni-
trate.90 During the reaction, the CN bond of the
thiosemicarbazone was cleaved. The remaining ligand partially
hydrolyzed under formation of 4,6-diacetylresorcinol, which
coordinated to the uranyl ions under the formation of a
tetrameric, macrocyclic compound.
1
was confirmed by their H NMR signal at 11.30 ppm. Single
crystals of (NBu4)2[{UO2(L1)}4(OEt)2(HOEt)2] were ob-
tained from a CH2Cl2/EtOH mixture. Unfortunately, due to
unsatisfactory crystal quality, the refinement stopped at an R1
value of 0.11. Thus, a detailed discussion of the bond lengths
and angles is not be done here. But, general bonding features
and the molecular structure of the compound can certainly be
derived. The coordination sphere of each uranyl moiety is
completed by two S,O chelates and each one ethanolato and/
or one ethanol ligand. The previously discussed intramolecular
π−π interactions between the central phenyl units are also
found in the [{UO2(L1)}4(OEt)2(HOEt)2]2− anion, the
structure of which is shown in Figure 4.
While the reactions of uranyl compounds with ligand H2L1
push the actinide into the less favored S,O coordination, the
pyridine-centered ligands H2L2 provide more coordination
modes, which may also include tri- or pentadentate arrange-
ments, as is shown for the conformations B and C (see Chart
3). DFT calculations on H2L2a were performed to determine
the preferred conformation of the ligand (for details, see
Supporting Information). Unlike the situation at ligand H2L1,
the bifunctional conformation A is disfavored and the chelator-
type conformations B and C are preferred. This preference
may have to do with the opportunity of the formation of
intramolecular hydrogen bonds, but it will at least support the
formation of metal chelates under participation of the central
pyridine ring.
The decomposition of H2L2a and H2L2b can be avoided
when a supporting base is added. This allows the
deprotonation of the ligands and their coordination in favor
of their hydrolysis. Chelate coordination of {L2a}2− and {L2b}2−
with uranyl ions was obtained when two drops of triethylamine
were added to the reaction mixtures. A compound of the
composition [UO2(L2a)(MeOH)] was obtained from the
reaction of H2 L2 a
, a uranyl source such as
[UO2 (CH3 COO)2 ]·2H2 O, (NBu4 )2 [UO2 Cl4 ], or
[UO2(NO3)2]·6H2O and NEt3 in methanol. Slow evaporation
of the reaction mixtures at room temperature gave single
crystals of the compound (Scheme 3). Dissolution of the
complex in a coordinating solvent such as DMF led to an
exchange of the coordinated methanol ligand, and [UO2(L2a)-
H
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(DMF)]·(DMF) was obtained after the slow evaporation of
the solvent at room temperature. The IR spectrum of
[UO2(L2a)(MeOH)] shows the strong asymmetric νUO
band at 912 cm−1 and the νOH band at 3211 cm−1, while the
spectrum of [UO2(L2a)(DMF)]·(DMF) shows the νUO
stretch at 904 cm−1. The carbonyl bands appear at 1654
cm−1 for [UO2(L2a)(MeOH)] and at 1629 cm−1 for
[UO2(L2a)(DMF)]·(DMF). This corresponds to a batho-
chromic shift of only 26 and 51 cm−1 with respect to the values
in H2L2a. These values strongly indicate that the CO
functionality is not involved in the coordination. The absence
of the N−H vibration suggests the deprotonation of the ligand,
which is confirmed by the 1H NMR spectrum. The ESI+ mass
spectra show the fragments [{M-solv}+K]+ at m/z = 702.1331
and [{M-solv}+Na]+ at m/z = 686.1625. Interestingly, the
cluster fragments [{M-solv}2+K]+ at 1365.3036 and [{M-
solv}2+Na]+ at 1349.3322 were observed. Figure 5 shows the
Table 2. Selected Bond Lengths (Å) and Angles (deg) in
[UO2(L2a)(MeOH)], [UO2(L2a)(DMF)],
a
[UO2(L2b)(H2O)], and [UO2(L2b)(DMF)]
[UO2(L2a-) [UO2(L2a)- [UO2(L2b)- [UO2(L2b)-
(MeOH)]
(DMF)]
(H2O)]]
(DMF)]
U1−O1
U1−O2
U1−S1
U1−S11
U1−N3
U1−N13
U1−N26
U1−O31
O1−U1−O2
O31−U1−S1
O31−U1−N3
O31−U1−N26
O31−U1−N13
O31−U1−S11
N26−U1- N3
N26 −U1-S1
N26−U1−N13
N26−U1−S11
1.776(2)
1.782(2)
2.9796(9)
2.9685(9)
2.508(3)
2.438(3)
2.600(3)
2.490(2)
178.1(1)
66.44(6)
121.31(8)
161.61(8)
122.19(8)
66.94(6)
60.32(8)
114.06(6)
60.68(9)
114.67(6)
1.748(7)
1.760(6)
2.939(2)
2.913(3)
2.514(8)
2.515(8)
2.624(7)
2.440(6)
178.2(3)
65.4(2)
120.3(2)
168.8(2)
120.3(2)
65.2(2)
61.1(2)
114.3(2)
61.1(2)
1.772(3)
1.779(3)
2.882(1)
2.933(1)
2.512(3)
2.538(3)
2.601(3)
2.490(3)
179.7(1)
64.72(8)
120.7(1)
165.1(1)
120.6(1)
64.72(8)
61.0(1)
1.768(5)
1.758(5)
2.924(2)
2.932(2)
2.512(5)
2.536(6)
2.608(5)
2.435(5)
179.6(5)
64.9(1)
120.3(2)
166.5(2)
121.0(2)
65.9(1)
60.4(2)
114.6(1)
61.1(2)
114.93(8)
60.9(1)
114.93(8)
114.2(2)
114.2(1)
a
The atomic labeling scheme of the latter two compounds has been
adopted from the {L2a}2− complexes in Figure 5.
mode as is observed in [UO2(L2a)(MeOH)] with a
coordinated water molecule instead of methanol. [UO2(L2b)-
(H2O)] crystallizes in the orthorhombic space group Pbca.
Also here, the water molecule can be replaced by the
dissolution of the compound in DMF. The resulting
[UO2(L2b)(DMF)] crystallizes in the monoclinic space
group P21/c. The structures of the complexes with the
{L2b}2− ligand are virtually identical to those with the diethyl
amine-substituted ones. Thus, no extra figures are included
with the molecular structures of these compounds. They can
be found in the Supporting Information. Selected bond lengths
and angles, however, are compared with the values obtained for
[UO2(L2a)(MeOH)] and [UO2(L2a)(DMF)] in Table 2.
Similarly to the complexes with {L2a}2−, analyses of the mass
spectra of the mononuclear complexes [UO2(L2b)(H2O)] and
[UO2(L2b)(DMF)] indicate the loss of the solvent molecules
during the measurements and the formation of dimeric
fragments [{M-(solv)}2+Na]+ with a mass peak at m/z =
1405.2538 and even trimeric fragments [{M-(solv)}3+Na]+
(m/z = 2096.3828). Although the structures of the resulting
complexes formed in the gas phase are not clear, their
formation describes the trend of such compounds to form
oligomeric units.
Oligomerization of the mononuclear uranyl complexes is
also observed, when the reaction of uranyl salts is done with an
equivalent amount of H2L2 or when the [UO2(L2)(MeOH/
H2O)] complexes are treated with an additional amount of
NEt3. This is exemplarily discussed for (HNEt3)2[{UO2(L2a)-
(μ2-OMe)}2], which was obtained as a yellow solid from the
treatment of a solution of [UO2(L2a)(MeOH)] in methanol
with two drops of NEt3. The IR spectrum of the compound
shows the absence of NH vibrations, which confirms the
deprotonation of the organic ligand in the compound. A strong
absorption observed at 1589 cm−1 can be assigned to the νCO
stretching vibration. In comparison, the νCO stretch of the
noncoordinated ligand is observed at 1680 cm−1, and the νCO
Figure 5. Molecular structures of (a) [UO2(L2a)(MeOH) and (b)
[UO2(L2a)(DMF)]. Hydrogen atoms except for the coordinated
methanol were omitted for clarity.
molecular structures of [UO2(L2a)(MeOH)] and [UO2(L2a)-
(DMF)]. Selected bond lengths and angles are given in Table
2. The uranium atoms in both structures have a distorted
hexagonal-bipyramidal coordination sphere with the oxido
ligands in the axial positions. The ligands {L2a}2− coordinate
pentadentate with three nitrogen and two sulfur atoms. The
hexagonal base is completed by the coordination of a solvent
molecule. The uranyl bond lengths with values between
1.748(7) and 1.782(2) Å and with OUO bond angles of
178.1(1) and 178.2(3)° are unexceptional. The U−N bond
lengths are in the range of 2.438(3)−2.514(8) Å for the
thiourea sites and between 2.600(3) and 2.624(7) Å for the
pyridine rings.
Reactions of H2L2b with uranyl acetate or (NBu4)2[UO2Cl4]
in the presence of 2 drops of triethylamine give yellow
precipitates, which were recrystallized from a 1:1 mixture of
CH2Cl2/MeOH (v/v) and characterized as [UO2(L2b)(H2O)]
(Scheme 2). [UO2(L2b)(H2O)] shows the same coordination
I
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
stretch of the monomeric complex [(UO2(L2a)(MeOH)] is
observed at 1654 cm−1. The significant bathochromic shift
strongly suggests the coordination via the carbonyl oxygen
atoms. Similar shifts have also been observed for other metal
complexes after chelate formation of H2L2a, which indicates
strong electron delocalization inside the chelate rings.60,61 The
presence of uranyl ions is confirmed by νUO stretching
vibrations observed at 912 cm−1.
Yellow crystals suitable for X-ray diffraction analysis were
obtained from a 1:1 mixture of CH2Cl2/MeOH (v:v) at room
temperature. The analysis of the X-ray data as well as the
results of the elemental analysis confirm the composition of the
complex as (HNEt3)2[{UO2(L2a)(μ2-OMe)}2]. Figure 6 shows
the structure of the complex anion [{UO2(L2a)(μ2-OMe)}2]2−.
Selected bond lengths and angles are listed in Table 3.
bonded {L2a}2− ligand. The subunits are connected by two
methanolato ligands. Thus, each uranium atom is sevenfold
coordinated with a pentagonal-bipyramidal geometry. The
uranyl bond lengths are in the range of 1.765(6)−1.783(6) Å.
The U−O bond lengths in the equatorial plane are in the range
of 2.348(6)−2.376(5) Å, while the U−N bonds are between
2.579(7) and 2.564(7) Å. The carbonyl bonds of 1.31(1) Å are
significantly longer than the distance of 1.223(5) Å, which is
observed in the noncoordinated ligand H2L2a and therefore in
the expected range for chelate complexes. The equatorial
positions of the pentagonal-bipyramidal coordination spheres
of the uranium atoms are almost perfectly planar. The
maximum deviation from the equatorial mean least-squares
plane of 0.142 Å is observed for N46.
An interesting structural feature of the [{UO2(L2a)(μ2-
OMe)}2]2− anion is the orientation of the bridging
methanolato ligands and the sulfur atoms with regard to the
equatorial plane. Both point to the same direction and, thus,
form the syn,syn-conformer of the complex as is depicted in
Figure 6.
The experiments described above show that the [{UO2(L2)-
(solv)] complexes are not stable in solution and readily replace
their H2O or MeOH ligands. Even a complete rearrangement
of the coordination mode of the {L2}2− ligands from
pentadentate S,N,N,N,S chelates to an O,N,O coordination
was observed during the formation of the [{UO2(L2)(μ2-
OMe)}2]2− anions, and also, the latter dimeric ions seems to
be unstable in solutions. This was first concluded from the 1H
NMR spectra of the compound measured in CDCl3 and
(CD3)2SO. The signals of the deprotonated ligand {L2a}2− and
the signals corresponding to the counterions {HNEt3}+ were
readily observed in both solvents. Those of the bridging
methanolato ligand, however, could not be resolved in CDCl3.
This may indicate a decomposition of the dimeric complex in
solution, the formation of (most probably monomeric) species
with solvent molecules (e.g., MeOH, H2O). The missing signal
for the coordinated methanolato ligands indicates a fast
exchange with other donor ligands (e.g., OH−/H2O). The H
1
NMR spectrum of (HNEt3)2[{UO2(L2a)(μ2-OMe)}2] in
(CD3)2SO, however, shows a signal at 3.13 ppm, which can
be assigned to noncoordinated methanol, resulting from a
complete replacement of these ligands in the coordination
sphere of uranium. These findings are supported by the
negative-mode ESI mass spectrum of the complex, which has
been measured in CHCl3/MeOH. The peak of the molecular
ion [{UO2(L2a)(μ2-OMe)}2]2− was not observed, but different
peaks were observed, which indicate the decomposition of the
complex in solution or in the gas phase. The two main peaks
observed at m/z = 680.1775 and 694.1932 can be assigned to
the monomeric anions [UO2(L2a)(OH)]¯ and [UO2(L2a)-
(OMe)]¯.
Figure 6. Structure of the complex anion of (HNEt3)2[{UO2(L2a)(μ2-
OMe)}2] with a depiction of the found syn,syn-arrangement of the
methanolato ligands and the sulfur atoms of the thiourea units.
Hydrogen atoms were omitted for clarity.
Table 3. Selected Distances (Å) and Angles (deg) in syn,syn-
(HNEt3)2[{UO2(L2a)(μ2-OMe)}2]
U1−O1
U1−O2
U1−O5
U1−O15
U1−N46
U1−O61
U1−O62
U1···U2
O1−U1−O2
O1−U1−N46
O1−U1−O5
O1−U1−O15
O1−U1−O61
O1−U1−O62
1.765(6)
1.770(6)
2.357(6)
2.376(5)
2.579(7)
2.348(6)
2.365(5)
3.772(5)
178.5(3)
90.7(3)
U2−O11
U2−O12
U2−O25
U2−O35
U2−N56
U2−O61
U2−O62
1.776(6)
1.783(6)
2.380(6)
2.372(6)
2.564(7)
2.336(6)
2.344(5)
The spectroscopic results are supported by the isolation of
orange-yellow crystals from a methanol/DMSO mixture of
(HNEt3)2[{UO2(L2a)(μ2-OMe)}2]. They consist of a mono-
nuclear compound of the composition [UO2(L2a)(DMSO)2]
as could be confirmed by a preliminary X-ray diffraction study.
The quality of the single crystals, however, was not suitable for
a detailed discussion of the bond lengths and angles. But the
molecular structure of the compound could be derived
unambiguously. It is shown in Figure 7. The {L2a}2− ligand
coordinates tridentate to the uranyl unit through an O,N,O
donor set and the coordination environment of the uranyl unit
is completed by two O-bonded dimethyl sulfoxide ligands.
O11−U2−O12
O11−U2−N46
O11−U2−O25
O11−U2−O35
O11−U2−O61
O11−U2−O62
179.0(3)
91.4(3)
88.2(3)
91.6(3)
91.7(3)
90.4(2)
89.1(3)
89.6(3)
91.2(3)
89.5(3)
The structure of [{UO2(L2a)(μ2-OMe)}2]2− consists of two
uranyl units, which are coordinated by each one O,N,O-
J
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 7. Molecular structure of [UO2(L2a)(DMSO)2].
Figure 8. Molecular structure of [{UO2(L3)]. Hydrogen atoms were
omitted for clarity.
Although the central pyridine ring of H2L2 considerably
changes the coordination properties of the bipodal aroyl-
thiourea ligands with uranyl ions compared to the behavior of
H2L1, the resulting complexes suffer from an inherent
instability, which is caused by the coordination of additional
solvent ligands and/or the pH-dependent formation of
binuclear species. A more stable complex is formed with
H2L3, which has a central bipyridine unit and, thus, should be
able to act as a hexadentate ligand.
distances observed in the compound (NBu4)2[{(UO2(L1)}4-
(OAc)2] with {L1}2− showing the S,O coordination pattern.
Liquid−liquid extraction processes play an important role in
the treatment of actinides and other heavy metals in waste
solutions and in recovery procedures. Well-established solvent
extraction methods for nuclear fuel recovery are processes such
as PUREX (plutonium and uranium recovery by extraction),
TALSPEAK (trivalent actinides lanthanides separation by
phosphorus-reagent extraction from aqueous complexes), or
SANEX (selective actinide extraction).91−93 Most of the
ligands used in such separation processes are phosphorus-
based derivatives, but research on the development of new
ligand systems to optimize selective extraction and back
extraction of actinides from their lanthanide counterparts is
still ongoing. Recently, a variety of ligand systems based on the
2,6-pyridine and 6,6′-(2,2′-bipyridine) scaffolds were success-
fully studied as extractants in the above-mentioned meth-
ods.94,95
To prove the potential suitability of the ligands discussed
above as possible extraction agents for uranyl ions, the stability
of (HNEt3)2[{UO2(L1)}4(OAc)2], [UO2(L2a)(MeOH)],
[UO2(L2b)(H2O)], and [UO2(L3)] in aqueous solutions was
studied. For this, CH2Cl2 solutions of the complexes were
mixed with the aliquots of aqueous solutions, the pH values of
which were adjusted with nitric acid. After vigorous shaking for
30 min, the phases were separated, and the distribution of the
uranyl ions between the two phases were determined
radiometrically.
Reactions of H2L3 with uranyl acetate or (NBu4)2[UO2Cl4]
in the presence of 2 drops of triethylamine give yellow
precipitates of [UO2(L3)] with yields of about 90%. The IR
spectrum of the product shows a strong νUO vibration at 908
cm−1 and the νCO stretch is detected at 1637 cm−1. The latter
frequency corresponds to a bathochromic shift of 70 cm−1 with
respect to the value in H2L3, which is slightly more than the
shift observed between [UO2(L2a)(MeOH)] and H2L2a. The
observed shift does not necessarily imply that the coordination
is established via the carbonyl group because in such cases the
bathochromic shift of the carbonyl band is more considerable
with values larger than 100 cm−1.60,61 Nevertheless, a strong
electron delocalization involving the CO group is indicated.
The absence of an NH vibration suggests the deprotonation of
the coordinated ligand. The positive-mode ESI mass spectrum
shows the expected molecular fragments [M + H]+ at m/z =
741.1991, [M + Na]+ at m/z = 763.1816 and [M + K]+ at m/z
= 779.1550. No dimerization or trimerization was detected,
indicating a higher stability of the compound compared to the
chelates formed with H2L2.
Single crystals suitable for X-ray analysis were obtained from
a solution of a 1:1 mixture of CH2Cl2/MeOH (v/v). Figure 8
shows the molecular structure of [UO2(L3)]. Selected bond
lengths and angles are listed in Table 4. Expectedly, the organic
ligand coordinates as a hexadentate ligand to the uranyl moiety
via four nitrogen and two sulfur atoms, giving a hexagonal-
bipyramidal coordination of the metal ion. The uranyl bond
lengths are 1.769(2) and 1.772(2) Å and the OUO bond
angle is 176.0(1). The hexagonal plane of [UO2(L3)] is almost
perfectly planar, with a maximum deviation of 0.17 Å for atom
N3 from the mean least-squares plane formed by the donor
atoms of the equatorial plane of U1. The U−N bond lengths
are between 2.517(3) and 2.518(3) Å for the thiourea sites and
2.609(3) and 2.610(3) Å for the bipyridine nitrogen atoms.
The U−S distances are 2.88(1) Å. This value is 0.05 Å shorter
than the value of the U−S bond lengths observed in
[UO2(L2a)(MeOH)], where {L2a}2− shows the same coordi-
nation pattern. However, it is equal to the value of the U−S
(HNEt3)2[{UO2(L1)}4(OAc)2], [UO2(L2a)(MeOH)], and
[UO2(L2b)(H2O)] are not stable in acidic aqueous solutions.
They rapidly decompose, and the released uranyl ions move to
the aqueous phase. Optically, in the case of the complexes
[UO2(L2a)(MeOH)] and [UO2(L2b)(H2O)], the solvent
mixtures became turbid, which indicates the formation of
less soluble hydrolyzed species.
The extraction of uranyl ions into the aqueous phase
increases with decreasing pH (see Figure 9). (HNE-
t3)2[{UO2(L1)}4(OAc)2], where the uranyl ion is bounded
via the bidentate S,O coordination, is the most unstable
complex with a uranyl nitrate formation of 60% already at pH 7
and 98% at pH 1. The monomeric complexes [UO2(L2a)-
(MeOH)] and [UO2(L2b)(H2O)] show a similar behavior
with extraction rates at neutral pH of around 20% and >70% at
pH 1. Such a behavior is not unexpected, keeping in mind the
reaction of H2L2 with uranyl nitrate, which results in an
immediate ligand cleavage and the formation of
K
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 4. Selected Bond Lengths (Å) and Angles (deg) in [UO2(L3)]
bond lengths
U1−O1
U1−O2
U1−S1
U1−S11
U1−N3
C14−N13
1.769(2)
1.772(3)
2.88(1)
2.88(1)
2.517(3)
1.353(5)
U1−N13
U1−N26
U1−N36
C2−S1
2.518(3)
2.609(3)
2.610(3)
1.706(4)
1.718(4)
C4−O5
C14−O15
C2−N3
C4−N3
C12−N13
1.232(4)
1.229(4)
1.380(5)
1.346(5)
1.370(5)
C12−S11
bond angles
O1−U1−O2
O1−U1−N36
O2−U1−N36
N3−U1−S11
N3−U1−N26
176.0(1)
92.0(1)
85.0(1)
119.9(7)
62.0(9)
N13−U1−S1
120.0(7)
83.0(1)
93.0(1)
88.9(9)
93.9(8)
O1−U1−N13
O2−U1−N13
N13−U1−N36
O1−U1−S11
O2−U1−S11
87.0(1)
92.0(1)
61.8(9)
94.5(9)
89.4(9)
O1−U1−N26
O2−U1−N26
O1−U1−S1
O2−U1−S1
Figure 9. (a) Uranyl extraction from the synthesized complexes into an aqueous nitric acid solution at different pH values. Concentration of the
complexes: 0.4 mM (in CH2Cl2); T = 23 °C. (b) pH dependence of the uranyl extraction from [UO2(L3)] at high acidic concentrations.
[UO2(dipicolinate)(H2O)]6 (vide supra). More stable is
[UO2(L3)]. It shows almost no release of the metal ion from
pH 7 to pH 1 with extraction values ≤1% (see Figure 9). The
formation of uranyl ions from the organic phase of [UO2(L3)]
was observed only at high acid concentrations. In half-
concentrated HNO3 solution, a uranyl extraction of 80% was
observed after 30 min. A complete extraction of the uranyl ions
from [UO2(L3)] was obtained in concentrated nitric acid
(Figure 9).
The release of the uranyl ions from the ligand frameworks
1
was also monitored spectroscopically with H NMR and UV/
vis. A comparison of the UV/vis spectra of the organic and
aqueous phases before and after the extraction procedure
clearly show that the extracted uranium species are not
L
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
identical with the used chelates (HNEt3)2[{UO2(L1)}4-
(OAc)2], [UO2(L2a)(MeOH)] or [UO2(L2b)(H2O)]. This
(2) Organometallic and Coordination Chemistry of the Actinides;
Albrecht-Schmitt, T. E., Ed.; Springer: Berlin, Heidelberg, 2008; Vol.
127.
1
behavior was confirmed by the H NMR spectra. In contrast,
the spectra of the extracted organic phase of [UO2(L3)] from
pH 7 to 1 show no differences to the spectrum of the
[UO2(L3)]. Decomposition was observed only in the spectra of
solutions with high acid concentrations.
(3) Hayton, T. W. Recent developments in actinide−ligand multiple
bonding. Chem. Commun. 2013, 49, 2956−2973.
(4) Ephritikhine, M. Recent Advances in Organoactinide Chemistry
As Exemplified by Cyclopentadienyl Compounds. Organometallics
2013, 32, 2464−2488.
(5) Liddle, S. T. The Renaissance of Non-Aqueous Uranium
Chemistry. Angew. Chem., Int. Ed. 2015, 54, 8604−8646.
(6) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Towards
uranium catalysts. Nature 2008, 455, 341−349.
CONCLUSIONS
■
A series of uranyl complexes with three types of bifunctional
aroylbis(N,N-dialkylthiourea) ligands was prepared and
characterized spectroscopically and by X-ray diffraction.
Mono-, di-, and tetranuclear compounds obtained from the
phenyl- or pyridine-centered ligands (H2L1 and H2L2) are
labile and readily undergo ligand exchange reactions or
hydrolysis. Remarkably stable is the neutral complex
[UO2(L3)] with the bipyridine-centered ligand. This complex
does not decompose even under moderately acidic conditions.
Preliminary experiments indicate that H2L3 does not form
stable complexes with lanthanides, which recommends further
experiments concerning selective uranium extraction from
lanthanide/uranium mixtures. Such studies are currently being
done in our laboratory.
(7) Moro, F.; Mills, D. P.; Liddle, S. T.; van Slageren, J. The
Inherent Single-Molecule Magnet Character of Trivalent Uranium.
Angew. Chem., Int. Ed. 2013, 52, 3430−3433.
(8) Liddle, S. T.; van Slageren, J. Improving f-element single
molecule magnets. Chem. Soc. Rev. 2015, 44, 6655−6669.
(9) Gardner, B. M.; Liddle, S. T. Small-Molecule Activation at
Uranium(III). Eur. J. Inorg. Chem. 2013, 2013, 3753−3770.
(10) Hohloch, S.; Garner, M. E.; Parker, B. F.; Arnold, J. New
supporting ligands in actinide chemistry: tetramethyltetraazaannulene
complexes with thorium and uranium. Dalton Trans. 2017, 46,
13768−13782.
(11) Andrews, M. B.; Cahill, C. L. Uranyl bearing hybrid materials:
synthesis, speciation and solid state structures. Chem. Rev. 2013, 113,
1121−1136.
(12) Frisch, M.; Cahill, C. L. Synthesis, structure and fluorescent
studies of novel uranium coordination polymers in the pyridinedi-
carboxylic acid system. Dalton Trans. 2006, 4679−4690.
(13) Carter, K. P.; Kalaj, M.; Cahill, C. L. Harnessing uranyl oxo
atoms via halogen bonding interactions in molecular uranyl materials
featuring 2,5-diiodobenzoic acid and N-donor capping ligands. Inorg.
Chem. Front. 2017, 4, 65−78.
(14) Lussier, A. J.; Lopez, R. A. K.; Burns, P. C. A Revised and
Expanded Structure Hierarchy of Natural and Synthetic Hexavalent
Uranium Compounds. Can. Mineral. 2016, 54, 177−283.
(15) Zhang, Z.; Senchyk, G.; Liu, Y.; Spano-Franco, T.;
Szymanowski, J.; Burns, P. Porous uranium diphosphonate frame-
works with trinuclear units template by organic ammonium
hydrolyzed from amine solvents. Inorg. Chem. 2017, 56, 13249−
13256.
(16) Qiu, J.; Spano, T.; Dembowski, M.; Kokot, A.; Szymanowski, J.;
Burns, P. C. Sulfate-Centered Sodium-Icosahedron-Templated Uranyl
Peroxide Phosphate Cages with Uranyl Bridged by μ-η1:η2 Peroxide.
Inorg. Chem. 2017, 56, 1874−1880.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01918.
■
S
Ellipsoid representations of the complexes, tables
containing X-ray data, structural parameters, and details
on DFT calculations and the extraction experiments
(PDF)
Accession Codes
CCDC 1549621−1549627 and 1851629 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, by emailing data_request@ccdc.cam.ac.uk, or by contacting
The Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(17) Serezhkina, L. B.; Grigor’ev, M. S.; Shimin, N. A.; Klepov, V.
V.; Serezhkin, V. N. First uranyl methacrylate complexes: Synthesis
and structure. Russ. J. Inorg. Chem. 2015, 60, 672−683.
(18) Serezhkina, L. B.; Vologzhanina, A. V.; Klepov, V. V.;
Serezhkin, V. N. Crystal Structure of R[UO2(CH3COO)3] (R =
AUTHOR INFORMATION
Corresponding Author
*E-mail: ulrich.abram@fu-berlin.de.
ORCID
Ulrich Abram: 0000-0002-1747-7927
Notes
The authors declare no competing financial interest.
■
+
NH4 , K+, or Cs+). Crystallogr. Rep. 2010, 55, 773−779.
(19) Carter, K. P.; Kalaj, M.; Kerridge, A.; Ridenour, J. A.; Cahill, C.
How to Bend the Uranyl Cation via Crystal Engineering. Inorg. Chem.
2018, 57, 2714−2723.
(20) Ridenour, J. A.; Cahill, C. L. Synthesis, structural analysis, and
supramolecular assembly of a series of in situ generated uranyl-
peroxide complexes with functionalized 2,2′-bipyridine and varied
carboxylic acid ligands. New J. Chem. 2018, 42, 1816−1831.
(21) Cambridge Crystallographic Database, vers. 5.39.
(22) Cantat, T.; Graves, C. R.; Scott, B. L.; Kiplinger, J. L.
Challenging the Metallocene Dominance in Actinide Chemistry with
a Soft PNP Pincer Ligand: New Uranium Structures and Reactivity
Patterns. Angew. Chem., Int. Ed. 2009, 48, 3681−3684.
ACKNOWLEDGMENTS
■
We gratefully acknowledge Ph.D. scholarships for C.N.N. from
the Rosa-Luxemburg Foundation and for C.T.P from DAAD
(German Academic Exchange Service). This paper contains
results which are part of the doctoral theses of C.N.N. (Freie
̈
̈
Universitat Berlin, 2018) and C.T.P. (Freie Universitat Berlin,
2016). See also refs 55 and ref 64.
(23) Ephritikhine, M. Molecular Actinide Compounds with soft
chalcogene ligands. Coord. Chem. Rev. 2016, 319, 35−62.
(24) Nief, F. Complexes containing bonds between group 3,
lanthanide or actinide metals and non-first-row main group elements
(excluding halogens). Coord. Chem. Rev. 1998, 178−180, 13−81.
REFERENCES
■
(1) Burns, C. J.; Eisen, M. S.. In The Chemistry of the Actinide and
Transactinide Elements; Morss, L. R., Edelstein, N. M., Fuge, J., Eds.;
Springer: Berlin, Heidelberg, 2006; Vol. 5.
M
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(25) Casellato, U.; Vidali, M.; Vigato, P. A. Actinide complexes with
chelating ligands containing sulfur and amidic nitrogen donor atoms.
Coord. Chem. Rev. 1979, 28, 231−277.
(26) Abram, U.; Schulz Lang, E.; Bonfada, E. Thiosemicarbazonato
Complexes of Uranium. Z. Anorg. Allg. Chem. 2002, 628, 1873−1878.
(27) Garcia Santos, I.; Abram, U. Synthesis and structures of
dioxouranium complexes with 2-pyridineformamide thiosemicarba-
zones. Inorg. Chem. Commun. 2004, 7, 440−442.
(28) Gaunt, A. J.; Scott, B. L.; Neu, M. P. Homoleptic uranium(III)
imidodiphosphinochalcogenides including the first structurally
characterised molecular trivalent actinide−Se bond. Chem. Commun.
2005, 3215−3217.
pyrrolidine-N′-(2-chloro-benzoyl)thiourea. J. Coord. Chem. 2006, 59,
223−228.
(45) Arslan, H.; Kulcu, N.; Florke, U. Synthesis and characterization
̈ ̈
̈
of copper(II), nickel(II) and cobalt(II) complexes with novel thiourea
derivatives. Transition Met. Chem. 2003, 28, 816−819.
(46) Sieler, J.; Richter, R.; Hoyer, E.; Beyer, L.; Lindqvist, O.;
Andersen, L. Kristall- und Molekulstruktur von Tris(1,1-diethyl-3-
̈
benzoyl-thioureato)ruthenium(III). Z. Anorg. Allg. Chem. 1990, 580,
167−174.
(47) Bensch, W.; Schuster, M. Crystal structure of tris(N,N-Diethyl-
N′-benzoylthioureato)cobalt (III), Co(C12H15N2OS)3. Z. Kristallogr.
1995, 210, 68.
(29) Gaunt, A. J.; Reilly, S. D.; Enriquez, A. E.; Scott, B. L.; Ibers, J.
A.; Sekar, P.; Ingram, K. I. M.; Kaltsoyannis, N.; Neu, M. P.
Experimental and Theoretical Comparison of Actinide and
Lanthanide Bonding in M[N(EPR2)2]3 Complexes (M = U, Pu, La,
Ce; E = S, Se, Te; R = Ph, iPr, H). Inorg. Chem. 2008, 47, 29−41.
(30) Gaunt, A. J.; Scott, B. L.; Neu, M. P. A Molecular Actinide−
Tellurium Bond and Comparison of Bonding in [MIII{N-
(TePiPr2)2}3] (M = U, La). Angew. Chem., Int. Ed. 2006, 45,
1638−1641.
(31) Ingram, K. I. M.; Kaltsoyannis, N.; Gaunt, A. J.; Neu, M. P.
Covalency in the f-element−chalcogen bond: Computational studies
of [M(N(EPH2)2)3] (M = La, U, Pu; E = O, S, Se, Te). J. Alloys
Compd. 2007, 444−445, 369−375.
(48) Huy, N. H.; Abram, U. Synthesis and Reactivity of Structurally
Analogous Phenylimido and Oxo Complexes of Rhenium(V) with
N,N-Dialkyl-N′-benzoylthioureas. Z. Anorg. Allg. Chem. 2008, 634,
1560−1564.
(49) Huy, N. H.; Abram, U. Rhenium and Technetium Complexes
with N,N-Dialkyl-N′-benzoylthioureas. Inorg. Chem. 2007, 46, 5310−
5319.
(50) Bensch, W.; Schuster, M. Komplexierung von Gold mit N,N-
Dialkyl-N′-benzoylthioharnstoffen: Die Kristallstruktur von N,N-
Diethyl-N′-benzoylthioureatogold(I)-chlorid. Z. Anorg. Allg. Chem.
1992, 611, 99−102.
(51) Braun, U.; Richter, R.; Sieler, J.; Yanovsky, A. I.; Struchkov, Y.
T. Kristall- und Molekulstruktur von Tris(1,1-diethyl-3-
̈
benzoylthioharnstoff)silber(I)-hydrogensulfid. Z. Anorg. Allg. Chem.
1985, 529, 201−208.
́
̈
(32) Cantat, T.; Arliguie, T.; Noel, A.; Thuery, P.; Ephritikhine, M.;
́
Le Floch, P.; Mezailles, N. The UC Double Bond: Synthesis and
Study of Uranium Nucleophilic Carbene Complexes. J. Am. Chem.
Soc. 2009, 131, 963−972.
(52) Koch, K. R.; Wang, Y.; Coetzee, A. Platinum(II) and
palladium(II) complexes of N-benzoyl-N′-propylthiourea (H2L):
synthesis and geometric isomer distribution of [M(H2L-S)2X2] (M
= PtII or PdII; X = Cl−, Br− or I−); crystal structure of trans-[Pd(H2L-
S)2Br2]. J. Chem. Soc., Dalton Trans. 1999, 6, 1013−1016.
́
́
(33) Tourneux, J.-C.; Berthet, J.; Thuery, P.; Mezailles, N.; Le Floch,
P.; Ephritikhine, M. Easy access to uranium nucleophilic carbene
complexes. Dalton Trans. 2010, 39, 2494−2496.
́
(34) Tourneux, J.-C.; Berthet, J.-C.; Cantat, T.; Thuery, P.;
̀
(53) Merdivan, M.; Duz, M.; Hamamci, C. Sorption behaviour of
́
Mezailles, N.; Le Floch, P.; Ephritikhine, M. Uranium(IV)
Nucleophilic Carbene Complexes. Organometallics 2011, 30, 2957−
uranium(VI) with N,N-dibutyl-N′-benzoylthiourea Impregnated in
Amberlite XAD-16. Talanta 2001, 55, 639−645.
2971.
(54) Zhao, Y.; Liu, C.; Feng, M.; Chen, Z.; Li, S.; Tian, G.; Wang, L.;
Huang, J.; Li, S. Solid phase extraction of uranium(VI) onto
benzoylthiourea-anchored activated carbon. J. Hazard. Mater. 2010,
176, 119−124.
́
(35) Tourneux, J.-C.; Berthet, J.-C.; Cantat, T.; Thuery, P.;
́
Mezailles, N.; Ephritikhine, M. Exploring the Uranyl Organometallic
Chemistry: From Single to Double Uranium−Carbon Bonds. J. Am.
Chem. Soc. 2011, 133, 6162−6165.
(55) Noufele, C. N. Uranium and Thorium Complexes with
(36) Beyer, L.; Hoyer, E.; Hartmann, H.; Liebscher, J.
Komplexbildung mit N-Acylthioharnstoffen. Z. Chem. 1981, 21,
81−91.
̈
Aroylbis(N,N-dialkylthioureas). Doctoral thesis, Freie Universitat
Berlin, 2018.
(56) Koch, K. R.; Bourne, S. A.; Coetzee, A.; Miller, J. J. Chem. Soc.,
Self-assembly of 2:2 and 3:3 metallamacrocyclic complexes of
platinum(II) with symmetrical, bipodal N′,N′,N‴N‴-tetraalkyl-
N,N″-phenylenedicarbonylbis(thiourea). J. Chem. Soc., Dalton Trans.
1999, 3157−3161.
(37) Koch, K. R. New chemistry with old ligands: N-alkyl- and N,N-
dialkyl-N′-acyl(aroyl)thioureas in coordination, analytical and process
chemistry of the platinum group metals. Coord. Chem. Rev. 2001,
216−217, 473−488.
̈
(38) Saeed, A.; Florke, U.; Erben, M. F. A review on the chemistry,
(57) Schwade, V. D.; Kirsten, L.; Hagenbach, A.; Lang, E. S.; Abram,
U. Indium(III), lead(II), gold(I) and copper(II) complexes with
isophthaloylbis(thiourea) ligand. Polyhedron 2013, 55, 155−161.
(58) Rodenstein, A.; Odendal, J. A.; Kirmse, K.; Koch, K. R.
Synthesis and molecular structure of the first binuclear {(bis-N-
isophthaloylureato)copper(II)pyridine}2 complex derived from the
{(bis-N-isophthaloyl-selenoureato)copper(II)}2 complex by O for Se
atom exchange. Inorg. Chem. Commun. 2011, 14, 99−102.
(59) Westra, A. N.; Bourne, S. A.; Koch, K. R. First metal-
lamacrocyclic complexes of Pt(IV) with 3,3,3′,3′-tetraalkyl-1,1′-
phenylenedicarbonylbis(thioureas): synthesis by direct or electrolytic
oxidative addition of I2, Br2 and Cl2. Dalton Trans. 2005, 17, 2916−
2924.
(60) Nguyen, H. H.; Thang, P. C.; Rodenstein, A.; Kirmse, R.;
Abram, U. Bipodal Acylthiourea Ligands as Building Blocks for Bi-,
Tetra-, and Polynuclear Oxorhenium(V) Complexes. Inorg. Chem.
2011, 50, 590−596.
(61) Nguyen, H. H.; Jegathesh, J. J.; Takiden, A.; Hauenstein, D.;
Pham, C. T.; Le, C. D.; Abram, U. 2,6-Dipicolinoylbis(N,N-
dialkylthioureas) as versatile building blocks for oligo- and
polynuclear architectures. Dalton Trans. 2016, 45, 10771.
coordination, structure and biological properties of 1-(acyl/aroyl)-3-
(substituted) thioureas. J. Sulfur Chem. 2014, 35, 318−355.
(39) Cîrcu, V.; Ilie, M.; Ilis,̧ M.; Dumitrasç u, F.; Neagoe, I.;
̆
Pasculescu, S. Luminescent cyclometallated platinum(II) complexes
with N-benzoyl thiourea derivatives as ancillary ligands. Polyhedron
2009, 28, 3739−3746.
́
̂
(40) Perez, H.; Mascarenhas, Y.; Plutín, A. M.; de Souza Correa, R.;
Duque, J. Tris(N-benzoyl-N′,N′-diphenylthioureato-κ2O,S)cobalt-
(III). Acta Crystallogr., Sect. E: Struct. Rep. Online 2008, 64, m503.
(41) Selvakumaran, N.; Ng, S. W.; Tiekink, E. R.; Karvembu, R.
Versatile coordination behavior of N,N-di(alkyl/aryl)-N′-benzoylth-
iourea ligands: Synthesis, crystal structure and cytotoxicity of
palladium(II) complexes. Inorg. Chim. Acta 2011, 376, 278−284.
(42) Fitzl, G.; Beyer, L.; Sieler, J.; Richter, R.; Kaiser, J.; Hoyer, E.
Kristall- und Moleku
thioureato)palladium(II). Z. Anorg. Allg. Chem. 1977, 433, 237−241.
(43) Richter, R.; Beyer, L.; Kaiser, J. Kristall-und Molekulstruktur
̈
lstruktur von Bis(1,1-diathyl-3-benzoyl-
̈
̈
̈
von Bis(1,1-diathyl-3-benzoylthioureato)kupfer(II). Z. Anorg. Allg.
Chem. 1980, 461, 67−73.
̈
̈
̈
(44) Arslan, H.; Florke, U.; Kulcu, N.; Emen, M. F. Crystal structure
and thermal behaviour of copper(II) and zinc(II) complexes with N-
N
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(62) Pham, C. T.; Nguyen, H. H.; Hagenbach, A.; Abram, U.
Iron(III) Metallacryptand and Metallacryptate Assemblies Derived
from Aroylbis(N,N-diethylthioureas). Inorg. Chem. 2017, 56, 11406−
11416.
(63) Wioppiold, T. A.; Ackermann, J.; Schulz Lang, E.; Abram, U.
Bi- and tetranuclear oxidorhenium(V) complexes with a bipodal
pyrroloylthioureato ligand. Polyhedron 2015, 87, 202−207.
(64) Pham, C. T. Oligonuclear complexes derived from aroylbis-
(77) Spek, A. L. PLATON: A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, Netherlands, 1980−2014.
(78) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
(79) Sheldrick, G. M. Crystal structure refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.
(80) Brandenburg, K. Diamond- Crystal and Molecular Structure
Visualization, vers. 4.5.1; Crystal Impact GbR: Bonn, Germany, 2018.
(81) Yokoyama, M.; Ikuma, T.; Obara, N.; Togo, H. Synthesis of
mesoionic triazoline nucleosides. J. Chem. Soc., Perkin Trans. 1 1990,
3243−3247.
̈
(N,N-dialkylthioureas). Doctoral thesis, Freie Universitat Berlin,
2016.
(65) Douglass, I. B.; Dains, F. B. Some Derivatives of Benzoyl and
Furoyl Isothiocyanates and their Use in Synthesizing Heterocyclic
Compounds. J. Am. Chem. Soc. 1934, 56, 719−721.
(66) Sharmoukh, W.; Allam, N. K. TiO2 Nanotube-Based Dye-
Sensitized Solar Cell Using New Photosensitizer with Enhanced
Open-Circuit Voltage and Fill Factor. ACS Appl. Mater. Interfaces
2012, 4, 4413−4418.
̈
(82) Schroder, U.; Beyer, L.; Sieler, J. Synthesis and X-ray structure
of a new silver(I) coordination polymer assembled as one-dimen-
sional chains. Inorg. Chem. Commun. 2000, 3, 630−633.
(83) Perry, D. L.; Templeton, D. H.; Zalkin, A. Structure of
diethylammonium ethoxybis(diethylmonothiocarbamato)-
+
dioxouranate(VI), (C2H5)2NH2 [UO2((C2H5)2NCOS)2OC2H5]−.
Inorg. Chem. 1978, 17, 3699−3701.
̈
(67) SOROBAN. Freie Universitat Berlin, https://www.zedat.fu-
(84) Perry, D. L.; Templeton, D. H.; Zalkin, A. Synthesis and
structure of di-n-propylammonium ethoxybis(di-n-propylmonothio-
carbamato)dioxouranate(VI), a mixed-chelate alkoxide of uranium.
Inorg. Chem. 1979, 18, 879−881.
berlin.de/HPC (accessed Sep 12, 2018).
(68) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson,
G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A.; Bloino, J.;
Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J.
V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.;
Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson,
T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.;
Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Throssell, K.; Montgomery, J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark,
M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith,
T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant,
J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.;
Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, J. L.; Morokuma, K.;
Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, Revision A.02;
Gaussian, Inc.: Wallingford, CT, 2016.
(69) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson,
G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.;
Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J.
V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.;
Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson,
T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.;
Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Throssell, K.; Montgomery, J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark,
M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.;
Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell,
A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.;
Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 16,
Revision A.03; Gaussian, Inc.: Wallingford, CT, 2016.
(85) Perry, D. L.; Zalkin, A.; Ruben, H.; Templeton, D. H. Synthesis,
characterization, and structure of a uranyl complex with a disulfide
ligand, bis(di-n-propylammonium) disulfidobis(di-n-
propylthiocarbamato)dioxouranate(VI). Inorg. Chem. 1982, 21,
237−240.
(86) Casellato, J.; Vigato, P. A.; Tamburini, S.; Graziani, R.; Vidali,
M. Uranyl complexes with bidentate derivatives of pyridine N-oxide.
The crystal structure of dimethylsulfoxidebis(1-oxo-2-thiopyridinato)-
dioxouranium(VI) and aquabis(1,2-dioxo-pyridinato)dioxouranium-
(VI) monohydrate. Inorg. Chim. Acta 1983, 72, 141−147.
(87) Jarvinen, G. D.; Ryan, R. R.; Smith, B. F.; Ritchey, J. M.
Preparation and crystal and molecular structures of uranyl complexes
of 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione and
the pyrazol-3-one analogue. Inorg. Chim. Acta 1987, 129, 139−148.
(88) Tourneux, J.-C.; Thuery, P.; Berthet, J.-C.; Ephritikhine, M.
Private CSD Communication, 2016, Refcode: AZIXOY.
(89) Immirzi, A.; Bombieri, G.; Degetto, S.; Marangoni, G. The
crystal and molecular structure of pyridine-2,6-dicarboxyl-
atodioxouranium(VI) monohydrate. Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1975, 31, 1023−1028.
́
́
(90) Gatto, C. C. Sıntese e Analise Estrutural de Complexos de
̂
Uranio(VI) com Hidrazonas, Semicarbazonas e Ligantes Relaciona-
dos. Doctoral thesis, UFSM Santa Maria, Brazil, 2006.
(91) Herbst, R. S.; Baron, P.; Nilson, M. Standard and Advanced
Separation: PUREX Processes for Nuclear Fuel Reprocessing; Woodhead
Publishing, Philadelphia, PA, 2011.
(92) Nilsson, K. L.; Nash, A. Review of the Development and
Operational Characteristics of the TALSPEAK Process. Solvent Extr.
Ion Exch. 2007, 25, 665−701.
(93) Magnusson, D.; Christiansen, B.; Foreman, M. R. S.; Geist, A.;
Glatz, J.; Malmbeck, R.; Modolo, G.; Serrano-Purroy, D.; Sorel, C.
Demonstration of a SANEX Process in Centrifugal Contactors using
the CyMe4-BTBP Molecule on a Genuine Fuel Solution. Solvent Extr.
Ion Exch. 2009, 27, 97−106.
(70) Vosko, S. H.; Wilk, L.; Nusair, M. Accurate spin-dependent
electron liquid correlation energies for local spin density calculations:
a critical analysis. Can. J. Phys. 1980, 58, 1200−1211.
(71) Becke, A. D. Density-functional thermochemistry. III. The role
of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652.
(94) Geist, A.; Mullich, U.; Magnusson, D.; Kaden, P.; Modolo, G.;
̈
Wilden, A.; Zevaco, T. Actinide(III)/Lanthanide(III) Separation Via
Selective Aqueous Complexation of Actinides(III) using a Hydro-
philic 2,6-Bis(1,2,4-Triazin-3-Yl)-Pyridine in Nitric Acid. Solvent Extr.
Ion Exch. 2012, 30, 433−444.
(72) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-
Salvetti correlation-energy formula into a functional of the electron
density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.
(73) Feller, D. The role of databases in support of computational
chemistry calculations. J. Comput. Chem. 1996, 17, 1571−1586.
(74) Schuchardt, K. L.; Didier, B. T.; Elsethagen, T.; Sun, L.;
Gurumoorthi, V.; Chase, J.; Li, J.; Windus, T. L. Basis Set Exchange: A
Community Database for Computational Sciences. J. Chem. Inf.
Model. 2007, 47, 1045−1052.
(95) Wilden, A.; Modolo, G.; Schreinemachers, C.; Sadowski, F.;
Lange, S.; Sypula, M.; Magnusson, D.; Geist, A.; Lewis, F. W.;
Harwood, L. W.; Hudson, M. J. Direct Selective Extraction of
Actinides (III) from PUREX Raffinate using a Mixture of
CyMe4BTBP and TODGA as 1-cycle SANEX Solvent Part III:
Demonstration of a Laboratory-Scale Counter-Current Centrifugal
Contactor Process. Solvent Extr. Ion Exch. 2013, 31, 519−537.
̈
̈
(75) Sheldrick, G. M. SADABS; Universitat of Gottingen: Germany,
2014.
(76) X-RED32; STOE & Cie GmbH: Darmstadt, Germany, 2002.
O
DOI: 10.1021/acs.inorgchem.8b01918
Inorg. Chem. XXXX, XXX, XXX−XXX