Coordination and extraction properties of 1,2-bis(diphenylphosphoryl)-benzene toward f-block element nitrates: Structural, spectroscopic and DFT characterization of the complexes

Article abstract of DOI:10.1016/j.poly.2021.115085

Reaction of 1,2-bis(diphenylpsphoryl)benzene 1,2-[Ph₂(O)P]₂C₆H₄ (L) with f-element nitrates resulted in 1:1 and 1:2 complexes. The isolated complexes, namely, [UO₂(L)(NO₃)₂]·MeCN

Full text of DOI:10.1016/j.poly.2021.115085

Polyhedron 198 (2021) 115085
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Coordination and extraction properties of 1,2-bis(diphenylphosphoryl)-
benzene toward f-block element nitrates: Structural, spectroscopic and
DFT characterization of the complexes
a
a
a
a
Anna G. Matveeva a, , Oleg I. Artyushin , Margarita P. Pasechnik , Adam I. Stash , Anna V. Vologzhanina ,
Sergey V. Matveev a, Ivan A. Godovikov a, Rinat R. Aysin a, Aleksandra A. Moiseeva a, Alexander N. Turanov b,
Vasilii K. Karandashev c, Valery K. Brel a
⇑
a Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow 119991, Russia
b Institute of Solid State Physics, Russian Academy of Sciences, Academician Osipyan str. 2, Chernogolovka 142432, Russia
c Institute of Microelectronics Technology Problems and High Purity Materials, Russian Academy of Sciences, Academician Osipyan str. 6, Chernogolovka 142432, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of 1,2-bis(diphenylpsphoryl)benzene 1,2-[Ph2(O)P]2C6H4 (L) with f-element nitrates resulted in
1:1 and 1:2 complexes. The isolated complexes, namely, [UO2(L)(NO3)2]ꢀMeCN (1), [UO2(L)2(NO3)](NO3)ꢀ
MeCN (2), [Th(L)2(NO3)3](NO3)ꢀMeCNꢀH2O (3), [La(L)2(NO3)3]ꢀ0.5MeCNꢀ1.5H2O (4), and [Lu(L)2(NO3)2]
(NO3)ꢀ2MeCN (5) have been characterized by elemental analysis and IR spectroscopy. The structures of
Received 20 November 2020
Accepted 1 February 2021
Available online 6 February 2021
complexes 1, 2, and 5 have been determined by single-crystal X-ray crystallography. Intraligand
p
-stack-
-stacking
interaction energy in two uranyl complexes 1 and 2 have been estimated from Bader’s AIM
Keywords:
ing and interligand CAH. . .
and CAH. . .
p interaction have been observed in the crystalline complexes. The p
1,2-bis(diphenylpsphoryl)benzene
f-element complexes
X-ray diffraction
Solution structure
Liquid extraction
p
theory calculations performed at the DFT level. Solution structure of all complexes has been investigated
by IR and multinuclear (1H, 13C, and 31P) NMR spectroscopy. The formation of 1:3 complexes with lan-
thanum nitrate (IR, 31P NMR) has been examined. Preliminary extraction study of U(VI), Th(IV), and Ln
(III) from 2 M HNO3 into 1,2-dichloroethane have shown that ligand L recovers U(VI), Th(IV), and La
(III) in the same extent as its tetraphosphoryl analog 1,2,4,5-[Ph2(O)P]4C6H2 (L’) but it recovers Eu(III),
and Lu(III) by several times better than L’. Furthermore, an improved modified method for the synthesis
of ligand L has been suggested.
Ó 2021 Elsevier Ltd. All rights reserved.
1. Introduction
benzene, which showed high efficiency in the recovery of f-block
elements, in particular U(VI), Th(IV), and Ln(III), from nitric acid
Phosphoryl-containing compounds are well-known and widely
used ligands for complexation with lanthanides and other f-block
elements [1–4]. They are extensively employed in liquid extraction
for the recovery, preconcentration, and separation of these ele-
ments [5–7]. Polydentate neutral organophosphorus compounds
show high efficiency in the recovery of actinides and lanthanides
from nitric acid solutions; as a rule, it is much higher than that
for monodentate analogs [8–12]. This feature favored to the devel-
opment of coordination chemistry of phosphoryl-containing
ligands, in particular, the studies of ability to coordinate ions of
f-block elements [13,14].
solutions [15]. It was of interest to study the extraction and coor-
dination properties of a structural analog of this compound whose
molecule contains only two rather than four Ph2P(O) groups: 1,2-
bis(diphenylphosphoryl)benzene (L). This compound is known as
efficient ligand for preparation of different complexes; however,
its complexes with f element nitrates are not described.
In this paper, we report the modified synthesis of the bisphos-
phoryl-containing ligand L and its new complexes with uranyl
(II), thorium(IV) and lanthanide(III) nitrates, the structural charac-
terization of the complexes in the solid state (X-ray, IR) and in
solution (IR, 31P NMR, 13C NMR, and 1H NMR), and extraction stud-
ies toward the f-block elements. Furthermore, we report herein the
results of AIM analysis (Bader’s ‘‘Atoms in molecules” approach)
Previously, we prepared
a
new neutral polyfunctional
organophosphorus ligand 1,2,4,5-tetrakis(diphenylphosphoryl)
for the
p-stacking interactions in two uranyl complexes. The
extraction ability of ligand L for the recovery of U(VI), Th(IV) and
Ln(III) from nitric acid solution into 1,2-dichloroethane (DCE) in
⇑
Corresponding author.
E-mail address: matveeva@ineos.ac.ru (A.G. Matveeva).
https://doi.org/10.1016/j.poly.2021.115085
0277-5387/Ó 2021 Elsevier Ltd. All rights reserved.

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
comparison with prototype, the 1,2,4,5-[Ph2P(O)]4C6H2 (L’), and
structure analog 1,2-[Ph2P(O)CH2]2C6H4 (L’’), containing the same
donor groups tethered to benzene platform via methylene linker,
(Scheme 1) was evaluated.
ions to form a hexagonal-bipyramidal UO8 coordination polyhe-
dron with uranyl oxygen atoms in the axial positions of the bipyra-
mid (Figs. 1, 2). As a whole, the complex is neutral and has
composition [UO2L(NO3)2]. Asymmetric unit of this compound
contains the complex in a general position and an acetonitrile
molecule.
2. Results and discussion
In complex 2, the uranium atom adopts a pentagonal bipyrami-
dal coordination, with four oxygen atoms from two molecules of L
and one oxygen atom of a nitrate anion in the equatorial plane
(Figs. 3, 4).
2.1. Synthesis of the ligand L
At present time, the literature reported a two-stage method for
the preparation of bis(phosphine oxide) L using 1,2-dihalobenzene
as an initial compound at the first stage. The 1,2-dihalobenzenes
used were dichloro, dibromo, and diiodo derivatives, which were
reacted in liquid ammonia with sodium diphenylphosphide. 1,2-
Bis(diphenylphosphinyl)benzene obtained in a yield not higher
35% was next oxidized into bis(phosphine oxide) L [16]. Further-
more, a method was described where diphenylphosphinous acid
was used as a phosphorus-containing reagent [17].
In this work, we prepared compound L by a modified procedure
including the same stages as described previously [16] but using
1,2-difluorobenzene in tetrahydrofuran solution (instead of incon-
venient liquid ammonia) followed by the oxidation of diphosphine
with 30% H2O2 (Scheme 2).
Steric hindrances from two bulky ligands do not allow them to
form a planar equatorial environment. The mean deviation of U1–
O1–O2–O3–O4 atoms from a plane is equal to 0.12 Å (Fig. 4), as
compared with 0.07(1) Å for U1 and all six oxygen atoms in the
equatorial plane of 1 (Fig. 2). The elongation of thermal ellipsoids
of oxygen atoms of L situated near the monodentate nitrate anion,
the disorder of the coordinated anion, and the prominent deviation
of the nitrate oxygen from the plane formed by the other atoms of
uranium(VI) equatorial plane (0.26(1) and –0.65(1) Å) also demon-
strate that there is not enough space in uranium(VI) equatorial
plane even for the monocoordinated anion (Figs. 3, 4), and it should
be rather labile. The unit cell of complex 2 contains the [UO2L2(-
NO3)]+ cation, a highly disordered uncoordinated nitrate anion,
and a disordered acetonitrile molecule.
This approach provided almost quantitative yields at both stages
for both products: the diphosphine and the target ligand L. We used
this approach previously in the synthesis of compound L’ [15].
As we mentioned above, the 1:2 complexes of lanthanides have
been obtained before. Lanthanides in previously obtained [LaL2(-
H2O)(EtOH)Cl2]Cl∙EtOH [18] and [EuL2(HFAA)2](HFAA) (HFAA is
hexafluoroacetylacetonate) [19] and the novel [LuL2(NO3)2](NO3)
(5) complexes are eight-coordinated (Figs. 5, 6).
2.2. Synthesis and solid-state characterization of the complexes
The lutetium(III) atom in the [LuL2(NO3)2]+ cation adopts square
antiprism geometry with oxygen atoms from bidentate chelate
ligand and NO–3 in the each prism bases (Fig. 5). The third nitrate
anion in complex 5 is uncoordinated; and the asymmetric unit of
this complex contains a half of cation, a half of uncoordinated
anion, and two independent acetonitrile molecules (each with half
occupancy).
Selected interatomic distances in these complexes as well as in
crystalline L∙CH2Cl2 [22] are listed in Table 1. Uranyl group in both
complexes is linear with O = U = O angles in [UO2L(NO3)2], and
[UO2L2(NO3)]+ equal to 176.9(1) and 179.1(3)°, respectively, while
r(U = O) are equal to 1.763(2) and 1.773(5) – 1.776(5) Å, respec-
tively. The U ꢁ OL distances in these complexes are nearly equal
(these vary from 2.338(2) to 2.365(2) and from 2.338(5) to 2.386
(4) Å), while the U ꢁ ONO3 distances for the chelate anion are longer
than for the monodentate anion (2.515(2) – 2.518(2) as compared
with 2.45(1) – 2.46(1) Å). Lanthanide contraction manifests itself
as a shortening of Ln ꢁ OL distances on passing from lanthanum
(III) (2.448(4) – 2.522(4) Å [18]) to lutetium(III) (2.219(2) – 2.223
(2) Å (Table 1)) complexes. The CAC and PAC bond distances
within the L ligand remain almost unchanged upon coordination,
with the P–CBz bonds being slightly longer than the P–CPh bonds.
However, the P@O distances upon coordination become longer
(Table 1).
The structure of complexes of ligand L with different metal salts
was described in a series of works [18–26]. The studied complexes
of ligand L with lanthanides were obtained using chloride [18]
iodide [18] and PF–6 [18] anions for La(III) and hexafluoroacetylace-
tonate for Eu(III) [19]. An effect of anions on the structure of the
complexes was noted [18]. In all studied complexes [18–26], ligand
L is coordinated in bidentate mode due to concerted orientation of
phosphoryl groups. To our best knowledge, the complexes of bis
(diphenylphosphoryl) ligand L with f element nitrates were not
described.
Mononuclear complexes of ligand L with f-element nitrates––
[UO2(L)(NO3)2]ꢀMeCN (1), [UO2(L)2(NO3)](NO3)ꢀMeCN (2), [Th
(L)2(NO3)4]ꢀCH3CNꢀH2O (3), [La(L)2(NO3)3]ꢀ0.5CH3CNꢀ1.5H2O (4),
[Lu(L)2(NO3)3]ꢀ2CH3CN (5)— were prepared by the reaction of sto-
ichiometric amounts of the ligand and the salts in MeCN. The com-
position and structures of the complexes in the solid state were
studied using elemental analysis, and IR spectroscopy. The struc-
tures of the crystal complexes 1, 2, 5 were also elucidated by X-
ray diffraction. All prepared complexes are readily soluble in
CH2Cl2.
2.2.1. X-ray structures
According to the data of single crystal X-ray diffraction, the
ditopic ligand acts as a bidentate-chelate one in both novel and
previously characterized complexes. Thus, the uranium(VI) atom
in complex 1 can interact also with two bidentate-chelate nitrate
Along with the P@O length change, the molecular conformation
of the ligand significantly varies upon coordination. One of Ph2P(O)
Scheme 1. Structure of bisphosphoryl ligand L and reference compounds L’, L’’.
2

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
Scheme 2. Synthesis of the ligand L.
Fig. 1. Molecular view of the complex 1 in representation of atoms with thermal
ellipsoids (given with 50% probability). Color code: C, grey; H, white; N, blue; O, red;
Fig. 3. Molecular view of the complex 2 in representation of atoms with thermal
ellipsoids (given with 50% probability). Color code: C, grey; H, white; N, blue; O, red;
U, green. The p-stacking and CAH. . . p intramolecular interactions are depicted as
dotted lines. (For interpretation of the references to colour in this figure legend, the
U, green. The
p-stacking interactions are depicted as dotted lines. (For interpreta-
tion of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
reader is referred to the web version of this article.)
Fig. 4. The closest environment of U(VI) atom in cation of complex 2. Oxygen atoms
in the equatorial plane are depicted in thermal ellipsoids.
Fig. 2. The closest environment of U(VI) atom in complex 1.
atom to the center of phenyl rings as short as 2.996(4), 2.793(4)
(Fig. 3), and 2.918(1) Å (Fig. 5). Thus, the
p-stacking interaction
moieties rotates around the P-CBz bond by ~105° and the distance
between the two P@O groups becomes ~0.3 Å shorter (Table 1).
Fig. 7 shows the changes in the conformation of ligand L upon
coordination.
between the two Ph substituents at two phosphorus atoms is
observed in molecule(s) of coordinated ligand L for all crystalline
complexes 1, 2, and 5.
Oxygen atoms of pure L are situated on the opposite sides of the
plane formed by the benzene ring and two phosphorus atoms and
on the same side for a coordinated ligand. As result, two of four
phenyl rings in the coordinated ligand become nearly coplanar
2.2.2. IR spectroscopy characterization
IR spectral data for ligand L and solid complexes 1–5 are pre-
sented in Table 2 (see also Figs. S1–S6).
and take part in
p
. . .
p
stacking interactions (Fig. 7). Intercentroid
The spectrum of complex 1 (Table 2, Fig. S2) corresponds to the
structure established by X-ray diffraction.
According to X-ray diffraction data, the structures of complexes
2 and 1 differ mainly by the coordination of nitrate ions, one of
which is coordinated in monodentate mode, while another anion
distances between the rings vary from 3.711(5) to 3.877(1) Å. In
the [UO2L2(NO3)]+ and [LuL2(NO3)2]+ cations, two intermolecular
interligand CAH. . .
dinated ligand can also be found with the distance from hydrogen
p contacts between adjacent molecules of coor-
3

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
features in the region of nitrate ions vibrations. The bands of
nitrate ions coordinated in bidentate mode may be certainly
revealed at 1512, 1288, and 1024 cmꢁ1, however, these bands have
relatively low intensity and are broadened more than usually
(Fig. S4). Although difference in mono- and bidentate nitrate coor-
dination is uncertain, the coordination number (CN) twelve for
thorium cation can be excluded in this case because of the bulky
spatial structure of ligand L and its bidentate coordination. The
structure [Th(O,O-L)2(O,O-NO3)2(O-NO3)2] with mono- and biden-
tate coordinated nitrate ions with CN 10 seems more likely. An
alternative structure is [Th(O,O-L)2(O,O-NO3)3]+(NO3)– (uncertain
absorption at ~ 1350 cmꢁ1).
Complex 4 was obtained as a fine-crystalline powder; however,
we failed to prepare crystals suitable for X-ray diffraction. IR spec-
trum (Table 2, Fig. S5) shows that both ligands are coordinated in
bidentate mode: a strong band at 1178 cmꢁ1 corresponds to
m
(P@O) vibrations. Nitrate ions are also coordinated, but it is not
excluded that one or two of them are bound in monodentate mode,
because the maxima of
1030 cmꢁ1, but each band has a low-frequency shoulder (high-fre-
quency band (NO3) is not determined because of Nujol absorp-
m(NO3) bands were revealed at 1317 and
m
tion). Therefore, CN of lanthanum cation is 9 or 8. Let us note
that the CN of metal in the crystalline complexes of ligand L with
lanthanum chloride [18] and the second group metal nitrates
(Mg, Ca, Ba, Sr [20]) was not larger than 8 according to X-ray
diffraction.
Fig. 5. Molecular view for cation of complex 5 in representation of atoms with
thermal ellipsoids. Color code: C, grey; H, white; Lu, pink; N, blue; O, red. The
p. . . p
and CAH. . . intramolecular interactions are depicted as dotted lines. (For
p
The spectrum of complex 5 (Table 2, Fig. S6) corresponds to the
structure established by X-ray diffraction.
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
2.3. Solution-state characterization of the complexes
The structure of the complexes in CD2Cl2 solutions was studied
by IR and multinuclear NMR spectroscopy. The selected parame-
ters of IR and 31P{1H}, 13C{1H} NMR spectra for the complexes 1–
5 in comparison with the data for the free ligand L are given in
Table 3 (see also Figs. S7–S13, and S14–S31).
The coordination of the P@O groups can be reliably determined
from the NMR spectra of compounds 1–5. The signals of the phos-
phorus nuclei exhibit expected downfield shifts by 5–18 ppm
(Table 3) close to those for the known complexes [18]. The signals
of carbon nuclei also show expected shifts. The signals dC(C-1,2)
and dC(C-10) in 13C{1H} NMR spectra are shifted upfield by 1–3
and ~5–8 ppm, respectively (Table 3). The signals of other carbon
atoms in the benzene platform are shifted downfield by ~2 ppm.
The signals of the phenyl substituents dC(C-40) and dC(C-20,60) exhi-
bit slightly larger downfield shifts than the dC(C-30,50) signals. The
signals of 1H NMR spectra are broadened for complexes 4, 5 and
considerably broadened for complexes 1, 2.
The IR spectrum of complex 1 solution (Fig. S8) is almost the
same as the spectrum of crystalline sample (Fig. S2), this fact
implies that the structure of the complex in solution is the same
as in crystal. However, the 31P{1H} NMR spectrum displays two sig-
nals at 49.0 and 46.4 ppm with integral intensity ratio of ~ 1:5
(Fig. S17). The 13C{1H} NMR spectrum also shows two sets of sig-
nals of different intensity (Fig. S19). The chemical shifts in both
spectra differ considerably from the signals of free ligand (Table 3)
and unambiguously indicate the bidentate coordination of ligand
molecule. We can suppose that we observe an equilibrium in
NMR time scale of two isomers of complex [UO2(O,O-L)(O,O-
NO3)2]0, where both nitrate ions are coordinated in bidentate mode
(dP = 46.4 ppm), and [UO2(O,O-L)(O,O-NO3)(O-NO3]0, where one
nitrate ion is coordinated in monodentate mode (dP = 49.0 ppm).
This assumption agrees well with quantum chemical calculations
on the existence of two such isomers (vide infra). Along with the
noted species in solution, the equilibrium may include a contact
ion pair (CIP) of complex [UO2(O,O-L)(O,O-NO3)]+ꢀ(NO3)– (the sig-
Fig. 6. The closest environment of Lu(III) atom in the cation of complex 5.
is free. The IR spectrum of the complex 2 shows no bands typical
for nitrate ion coordinated to uranyl ion in bidentate mode (see
Table 2, Fig. S3), but displays the bands at 1296 and ~1020 cmꢁ1
,
which may be attributed to vibrations of nitrate ion coordinated
in monodentate mode in accordance with the data for similar com-
plexes [20,27]. The band at 1344 cmꢁ1 belongs to vibration of free
nitrate ion.
Complex 3 was obtained as a white powder, we failed to pre-
pare crystals suitable for X-ray diffraction. The IR spectrum
(Table 2, Fig. S4) shows a band of coordinated P@O groups of both
ligand molecules at 1136 cmꢁ1. The IR spectrum shows certain
4

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
Table 1
Selected interatomic distances (Å) in compounds L, 1, 2, and 5.
Parameter
L [22]
1
2
5
Metal atom
U = O
U(VI)
1.763(2)
U(VI)
Lu(III)
1.773(5) – 1.776(5)
2.338(5) – 2.386(4)
2.45(1) – 2.46(1)
1.494(4) – 1.513(4)
1.778(9) – 1.808(5)
1.819(6) – 1.829(6)
3.711(5) – 3.733(5)
2.716(6) – 2.738(8)
M ꢁ OL
2.338(2) – 2.365(2)
2.515(2) – 2.518(2)
1.497(2) – 1.504(2)
1.787(3) – 1.796(3)
1.807(3) – 1.822(3)
3.846(2)
2.219(2)–2.223(2)
2.366(2) – 2.412(2)
1.495(2) – 1.503(2)
1.788(2) – 1.796(3)
1.817(2) – 1.818(2)
3.877(1)
M ꢁ ONO3
P@O
1.484(2) – 1.485(2)
1.7999(3) – 1.815(3)
1.824(3) – 1.838(3)
P ꢁ CPh
P ꢁ CBz
Cg. . .Cga
P@O. . .O@P
2.977(4)
2.681(3)
2.715(2)
a
The distance between the centers of two parallel Ph rings in the ligand L.
Table 2
Selected IR (m
, cmꢁ1) spectroscopic data for ligand L and its complexes with f-element
nitrates 1–5 in crystalline and solid state.
Compound
m
(P@O)
m
(NO3)
L
1203vs
–
1a
1160vs,
1146sh
1142vs,
1149sh
1136s
1517vs, 1490sh, 1288s 1273sh, 1264sh,
1027 m
2a
1470m br b, 1344m, 1296m, ~1020w
3
4
5
1512m, 1288m br, 1023w
1178vs
1167s, 1145s
*
c, 1317s, 1295sh, 1036w, 1031sh
a
~1500m, 1340m, 1305m, 1027w
aCrystalline compound.
bIn the spectrum of sample as a KBr pellet.
cExpected band of
(NO3) is obscured by the Nujol absorption.
m
The IR spectrum of complex 3 displays a split band of coordi-
nated P@O groups with maxima at 1143 an 1136 cmꢁ1 (Fig. S10).
The bands m
(NO3) appear at 1519 and 1288 cmꢁ1 and correspond
Fig. 7. Conformation of uncoordinated L (blue) as compared with the coordinated
molecules in complex 1 [UO2L(NO3)2] (red). Overlaid atoms are six carbon atoms of
the benzene ring, and two phosphorus atoms. (For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this
article.)
to NO3 groups coordinated in bidentate mode, however, these
bands have a complex form and unusual broadening. The band
of free nitrate ion is observed at 1352 cmꢁ1. One can suppose
that coordination polyhedron includes nitrate ions coordinated
in bi- and monodentate mode. The 31P{1H} and 13C{1H} NMR
spectra show one set of signals indicating the bidentate coordina-
tion of both ligand molecules (Fig. S23, S25). The signals in 1H
NMR are resolved and show fine structure (Fig. S24). One can
assume that complex 3 exists in solution as a solvent-separated
ion pair (SSIP) [Th(O,O-L)2(O,O-NO3)2(O-NO3)]+ꢀ(NO3)–, the CN of
thorium is 9.
nal at 49.0 is broadened). It should be noted that the presence of
two (and more) signals of coordinated P@O groups in 31P{1H}
NMR spectra for the complexes of phosphoryl-containing ligands
is infrequent and the observed equilibrium for certain compounds
is explained by change in anion coordination (monodentate, biden-
tate, free anion) in the species with different chemical shifts
[18,20,26,28]. The 1H NMR spectrum of complex 1 is considerably
broadened (Fig. S18), which indicates the presence of dynamic pro-
cesses in solution.
According to the data of IR spectroscopy (Table 3), the structure
of biligand uranyl complex in solution is similar to the structure in
crystal. The 31P{1H} NMR spectrum of solution shows two narrow
singlets at 46.5 and 46.3 ppm with integral intensity ratio
of ~ 5::1 (Fig. S20). The 13C{1H} NMR spectrum also exhibits two
sets of signals of different intensity (Fig. S21). The slight difference
in dP values (0.2 ppm) allows us to suppose that the monodentate
coordination of nitrate ions in both species retains, while the
observed difference can be explained by the existence of equilib-
rium of isomers of different structure (see below, Section 2.4).
The 1H NMR spectrum is considerably broadened, which indicates
the occurrence of dynamic processes. The equilibrium includes
ionic complexes [UO2(O,O-L)2(O-NO3)]+ꢀ(NO3)– and [UO2(O,O-
L*)2(O-NO3)]+ꢀ(NO3)– (L* are ligand molecules that differ by the
presence of additional intramolecular interactions), the coordina-
tion number of uranyl cation in both species is 5.
The IR spectrum of solution of complex 4, as distinct from the
spectrum of solid complex, exhibits
a
weak absorption at
(P@O) band of
1204 cmꢁ1 whose position coincides with that of
m
free phosphoryl group. An intense band of coordinated P@O groups
is observed at 1180 cmꢁ1 with a weak shoulder at ~ 1175 cmꢁ1
(Fig. S11). The broad unresolved band at ~ 1460 and the shoulder
at 1300 cmꢁ1 should be assigned to vibrations of nitrate ions coor-
dinated in bidentate mode, while the band at 1324 cmꢁ1 refers to
vibrations of monodentate nitrate ions. There is no band of free
nitrate ions (Fig. S11). The 31P{1H} and 13C{1H} NMR spectra dis-
play one set of signals indicating the bidentate coordination of
both ligand molecules (Fig. S26, S28). However, the signals in 1H
NMR spectrum are broadened (Fig. S27). One can suppose that
complex 4 in solution exists in equilibrium as a contact ion pair
(CIP) [La(O,O-L)2(O,O-NO3)2]+ꢀ(NO3)–, neutral complex [La(O,O-
L)2(O,O-NO3)(O-NO3)2]0, and a small portion of monoligand com-
plex [La(O,O-L)(O,O-NO3)3]0 whose emergence is accompanied by
the presence in solution of small amount of free ligand. In contrast
to IR time scale, these equilibria refer to fast processes in the NMR
time scale. Lanthanum cation CN is 8 in the all considered
structures.
5

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
Table 3
Selected IR (
m
, cmꢁ1), 31P{1H} and 13C{1H} NMR (d, ppm) spectroscopic data for the ligand L and its complexes 1–5 with f-element nitrates in CD2Cl2 (0.01 M) at 25 °C.
a
Compound
m
(P@O)
dP (W )
½
dC(C-1,2)
dC(C-10)
dC(C-3,6) dC(C-4,5)
m
(NO3) coord
mE(NO3)
free
L
1
1204s
1165s, 1146sh
30.7 (0.01)
136.70 dd 134.03 d
135.86t
137.47t
130.87 dt
133.00 dt
c
c
49.0 (0.24), 46.4 (0.07) 134.19
128.00 d
1525vs, 1495sh, 1288sh, 1270s,
1028w
–
b
c
ddc
2
1147s
46.5 (0.05), 46.3 (0.02) 134.04
127.86 d
137.57 t
133.03 dt
br
1470sh, 1387m, 1296m
1354m
d
c
c
ddc
3
4
1143sh,1136vs
1204sh,1180vs,
1175sh
44.9 (0.01)
35.4 (0.05)
133.21 dd 126.43 d
135.85 dd 129.44 d
137.84t
136.84t
133.13 dt
131.50 dt
1519s, 1288s
~1460sh br, 1324m, 1300sh
1352m
–
5
1204sh,1174vs,
1147sh
41.9 (0.05)
134.22 dd 127.29 d
137.86t
133.17 dt
1524m br, 1503m br, 1299s
1352s
aThe band width at half-height (in ppm).
bIntegral intensity ratio is ~1:5.
cMinor signals (see the corresponding figures in ESI).
dIntegral intensity ratio is ~5:1.
The IR spectrum of solution of complex 5 shows rather distinct
(P@O) band of free P@O group at 1204 cmꢁ1 along with the strong
Both values can be related to the chemical shifts of coordinated
phosphoryl groups in ionic complexes of lutetium with different
coordination of nitrate ions that vary ‘‘efficient charge” of cation
and the corresponding shielding of phosphorus atom [20,28]. Vari-
able temperature NMR spectroscopic study shows the existence of
two isomers of complex 5. One can assume that solution contains
[Lu(O,O-L)2(O,O-NO3)]2+ꢀ2(NO3)–, (dP = 45.2 ppm) and [Lu(O,O-
L)2(O,O-NO3)2]+ꢀ(NO3)–, (dP = 39.8 ppm) species in equilibrium at
200. K. While the main species is [Lu(O,O-L)2(O,O-NO3)(O-NO3)]+-
ꢀ(NO3)– (dP = 41.9 ppm) at 291 K. Along with these equilibria at
ambient temperature, the equilibrium also includes monoligand
complex [Lu(O,O-L)(O,O-NO3)3]0 and the corresponding amount
of free ligand whose band is detected in IR spectrum. These equi-
libria at ambient temperature are fast in the NMR time scale. The
CN of lutetium cation in the noted species is 6, 7, or 8.
By the example of reaction of ligand L with La(NO3)3, we exam-
ined the possibility to form complexes of composition La:L = 1:3.
The addition of equimolar amount of L to complex 4, IR spectrum
displays the emergence of absorption at 1350 cmꢁ1, which indi-
cates the appearance of free NO3 groups (Fig. S13). The remaining
spectrum is close to the spectrum of complex 4, it also shows a
weak absorption of free P@O groups at 1204 cmꢁ1. The 31P{1H}
m
band of coordinated P@O groups at 1174 cmꢁ1 with shoulder at
1147 cmꢁ1 (Table 3). The spectrum displays rather strong band
of free nitrate ions at 1352 cmꢁ1. The spectrum also exhibits the
broad split bands of NO3 groups at 1524 and 1503 cmꢁ1 and a band
at 1299 cmꢁ1 (Fig. S12). This spectral pattern may correspond to
the presence in solution of several complex species with free and
coordinated mono- and bidentate nitrate ions. The 31P{1H} and
13C{1H} NMR spectra show one set of signals indicating the biden-
tate coordination mode of both ligand molecules (Table 3, Fig. S29,
S31). The signals in 1H NMR spectrum are broadened (Fig. S30). The
31P{1H} NMR spectrum changes upon consecutive cooling to 200 K
(Fig. 8). One narrow singlet is observed at 291 K, it is broadened
and slightly shifted upon further cooling; the spectrum shows
two very broad resonances at 220 K and two singlets at 45.2 and
39.8 ppm of equal intensity at 200 K.
NMR spectrum of solution displays singlets at 36.9 (W = 0.5),
½
35.2 (W = 1.2), and 30.6 (W = 0.02) ppm with integral intensity
½
½
ratio of ~1:2.4:0.01 (Fig. S32). One can suppose that equilibrium in
solution involves trisligand complexes [La(O,O-L)3(O,O-NO3)]2+
-
ꢀ(NO3)– (dP = 36.9 ppm) and [La(O,O-L)3(O-NO3)2]+ꢀ(NO3)– (dP = 35.2-
ppm), as well as a small amount of bisligand complexes [La(O,O-
L)2(O,O-NO3)2]+ꢀ(NO3)–
and
[La(O,O-L)2(O,O-NO3)(O-NO3)2]0
(dP = 35.2–35.4 ppm), which is accompanied by the corresponding
amount of the free ligand (dP = 30.6 ppm).
Thus, the strong bidentate coordination of ligand retains in the
complexes 1–5 in CD2Cl2 solutions. The coordination of nitrate ions
varies from bi- to monodentate and to free nitrate ions within CIP
or SSIP. The cation of large radius La(III) can form trisligand catio-
nic complexes in solution.
2.4. DFT study and QTAIM analysis for complexes 1 and 2
The DFT analysis for monoligand complex [UO2L(NO3)2] and
cation of bisligand complex [UO2L2(NO3)]+ was performed at the
PBE/6-311G**, MWB60 level. All found isomers include the biden-
tate coordination of ligand molecules and intraligand pstacking.
The DFT results for monoligand complex [UO2L(NO3)2] revealed
two isomers: 1a (X-ray geometry) and 1b. In the structure 1a, both
nitrate ions are coordinated in bidentate mode (Fig. S33a, b), while
the structure 1b includes one of nitrate ions coordinated in mon-
Fig. 8. Variable temperature 31P{1H} NMR spectra (121.49 MHz) of complex 5ꢀin
CD2Cl2.
6

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
odentate mode (Fig. S34a, b). The
p
stacking energy in both isomers
values found in crystalline complexes 1 and 2 by X-ray diffraction.
One p-stacking and two p-stacking and two CH. . .p interactions
according to X-ray diffraction data are observed in crystalline com-
plexes 1 and 2, respectively (see above, Figs. 1, 3).
is the same, 1.1 kcalꢀmolꢁ1 (Ta,k. S1). Complex 1a is favored over
1b by 6.15 kcalꢀmolꢁ1 (Table 4).
For cation of bisligand complex [UO2L2(NO3)]+, we revealed four
isomers: two isomers 2a (X-ray geometry) (Fig. S35a, b) and 2b
(Fig. S36a, b) with monodentate nitrate coordination, and two iso-
mers 2c (Fig. S37) and 2d (Fig. S38) with bidentate nitrate coordi-
nation. The isomers of each pair 2a, 2b and 2c, 2d differ from each
other by the spatial arrangement of the ligand molecules. Let us
note that in the case of isomers 2a and 2c, we observed the forma-
2.5. Solvent extraction of f-block elements
To compare the efficiency and selectivity of the studied ligand L
as well as its tetraphosphoryl prototype L’ [15] and extractant L’’
[29] we studied the distribution ratios (D = [M]org/[M]aq) for ura-
nium(VI), thorium(IV), and several lanthanides(III) (Figs. 10, 11).
Fig. 10 shows that both ligands L and L’ almost similarly recover
thorium, but ligand L extracts uranium slightly better. Compound
L’’, where Ph2P(O) groups are bound to benzene platform via
methylene linkers, recovers uranium much worse and does not
recover thorium. This compound also does not recover lanthanides
(DLn < 0.003).
Extraction efficiency and selectivity is known to be dependent
in complicated manner on numerous factors, including the
strength and structure of extracted complexes, hydrophilicity/
lipophilicity balance of a ligand and its complexes.
In the case of close structure and the same coordination type of
ligands, we can analyze extraction data in the first approximation
by the comparison of composition and structure of extracted and
individual (model) complexes in solution. Let us note that the
lipophilicity of ligands L and L’ is close according to preliminary
data (the data will be reported elsewhere).
tion of two
moieties, whereas there are no CH. . .
and 2d. In all studied cases, -stacking and additional CH. . .
pstacking and two CH. . .
p
interactions in both ligand
contacts for isomers 2b
con-
p
p
p
tacts characterize two bond paths (Fig. 9a, b) (except for isomer 2d
containing one bond path).
The energy of
are juxtaposed in Table S1. The obtained
energy values for isomers of 1.2–2.4 kcal molꢁ1 (Table S1) are close
to those for intramolecular -stacking in a Co(III) complex [30] of
about 1–3 kcal molꢁ1 and to those for intramolecular
-stacking
interactions in UO2(II) complexes [31] of about 2.0–2.3 kcal molꢁ1
p
-stacking and CH. . .
p
contacts for the all isomers
p-stacking interaction
p
p
.
Isomers with monodentate coordination of nitrate ion 2a, 2b are
slightly more preferable than isomers 2c, 2d with nitrate ion coor-
dinated in bidentate mode approximately by 1.3–2.3 kcal molꢁ1
,
which also indicates the possibility of their simultaneous presence
in solution.
The obtained results (Table 4) agree well with the assumption
that solutions of complexes 1 and 2 contain equilibrium mixture
of species that differ considerably in
plex 1 and slightly differ in the case of complex 2.
The structure of individual complexes of ligand L’ is not studied
yet, but the composition of extracted species is known [15]. It was
found that species extracted into chloroform have metal:ligand
composition of 1:1.5 for U(VI) and 1:2 for Th(IV). One can suppose
that compound L will extract these actinides most likely as species
D
Go298 and dP values for com-
Let us note that the calculated interatomic distances and angles
in structures 1a (Fig. S33a) and 2a (Fig. S35a) generally agree with
Table 4
Relative energies of isomers of complex [UO2L(NO3)2] and isomers of complex cation [UO2L2(NO3)]+.
Isomer
Etot, a.u.
D
Etot, kcal/mol
Go298, a.u.
D
Go298, kcal/mol
1a (X-ray geometry)
g
2-NO3,
1-NO3
g
2-NO3
ꢁ3177.082162
ꢁ3177.071747
ꢁ4886.162741
ꢁ4886.164879
ꢁ4886.160258
ꢁ4886.162535
0.00
6.54
0.00
–1.56
1.34
+0.13
ꢁ3176.633075
ꢁ3176.623274
ꢁ4885.279905
ꢁ4885.280910
ꢁ4885.277871
ꢁ4885.277201
0.00
6.15
0.00
–0.63
1.28
1.70
1b
g g
1-NO3, 2-NO3
2aa (X-ray geometry)
g
2b
2ca
2d
g
g
g
1-NO3
2-NO3
2-NO3
a
CH. . .p contacts are present.
Fig. 9. The typical fragments of molecular graph exhibit the
orange (P), grey (C), white (H). The -stacking and CH. . . contact bond paths are shown as green dotted lines; BCPs (3;–1) are red. (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
p-stacking (a) and CH. . .p contacts (b) in the isomers of complexes 1 and 2. Color codes for the atoms: red (O),
p
p
7

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
Fig. 10. Comparison of the distribution ratios of U(VI) and Th(IV) for the extraction from 2 M HNO3 with 0.0001 M solutions of compounds L [this work], L’ [15] and 0.01 M
solution of compound L’’ [29] in DCE; the initial concentration of uranyl and thorium nitrates in the aqueous phase is 2 ∙ 10ꢁ6 M. (Color online.)
of the same composition as L’, both ligands seem to exhibit the
same denticity. Then one can expect that DU and DTh values will
be close for both extractants (as it is seen in Fig. 10).
Neutral complexes are known to be more lipophilic and better
extracted into organic solvent than ionic ones. This feature seems
to be one of the reasons of better recovery of U(VI) with both
extractants (Fig. 10) because U(VI) is extracted as a mixture of neu-
tral monoligand and ionic bisligand complexes in contrast to Th
(IV).
Fig. 11 shows that recovery efficiency for ligands L and L’ in the
series of studied Ln(III) varies in different manner. It was found
that compound L’ extracts Ln(III) as species with metal:ligand
composition of 1:2 [15]. Decrease of DLn in the series La–Lu is rea-
sonably explained by the decrease of cation radius for Ln, which
results in expulsion of nitrate ion and increase in the content of
ionic complexes if composition and coordination mode for ligand
L’ retains.
sion of the next nitrate ion and the growth of the content of poorly
extracted ionic pairs of complexes in solution. The aggregate action
of these factors leads to considerable difference in the profile of DLn
variations for the series of the studied lanthanides for L and L’
(Fig. 11).
In summary, the efficiency of La(III) recovery with ligand L’ is
almost twice as high as with ligand L. The efficiency of Eu(III)
and Lu(III) recovery with ligand L is higher than for its tetraphos-
phoryl analog by 9 and 80 times, respectively. Extraction selectiv-
ity also differs considerably. Separation factor for La and Eu (SLa/
= DLa/DEu) for ligand L is twice as high as for ligand L’.
Eu
The study of extraction properties of ligand L and the structure
of complexes of ligand L’ is in progress.
Taking into account the obtained data, we should emphasize
that bisphosphoryl ligand L is more convenient and promising can-
didate for the further study of f-element extraction than tetraphos-
phoryl compound L’.
Ligand L, as distinct from ligand L’, forms in solution ionic com-
plex with metal:ligand ratio of 1:3 (this work), which leads to
increase in the content of ionic less extracted species. Since the
strong chelate coordination of compound L retains in the all stud-
ied complexes, the composition of extracted species will approach
to 1:2 when Ln radius decreases, while recovery efficiency will
increase until further drop of Ln cation radius leads to the expul-
3. Conclusion
Coordination properties of the neutral organophosphorus
ligand L toward f-block element nitrates were examined. The bisli-
gand complexes of L with U(VI), Th(IV), La(III) and Lu(III) nitrates
were studied in the solid state (X-ray, IR) and solution (IR, 31P
NMR, 13C NMR, and 1H NMR). The bulky bisphosphoryl ligand L
exhibits constant PO,PO-denticity in all studied complexes both
in solid state and solutions. Nitrate ions show variable denticity.
We revealed bi- and monodentate coordination of nitrate ions
and even the presence of free uncoordinated ions. The extraction
experiments revealed that the studied bisphosphoryl ligand 1,2-
[Ph2P(O)]2C6H4 (L) recovers Th(IV) and U(VI) by the same extent
as its tetraphosphoryl prototype 1,2,4,5-[Ph2P(O)]4C6H2 (L’) and
extracts Eu(III) and Lu(III) considerably better than L’. Both ligands
L and L’ are considerably superior over the bisphosphoryl ligand
with methylene linkers between the phosphoryl group and the
benzene ring 1,2-[Ph2P(O)CH2]2C6H4 (L’’) in terms of the recovery
efficiency of f-block elements from nitric acid solutions in DCE.
4. Experimental
4.1. General
Fig. 11. Comparison of the distribution ratios of La(III), Eu(III), and Lu(III) for the
extraction from 2 M HNO3 solution with 0.02 M solutions of compounds L, L’’, and
0.01 M solution of compound L’ [15] in DCE; the initial concentration of lanthanide
nitrates in the aqueous phase is 2 ∙ 10ꢁ6 M.
Solvents were purified and dried using standard procedures
[32]. Deuterated solvents CD2Cl2 (99.9% D, Cambridge Isotope Lab-
8

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
oratories, Inc.) and CDCl3 (99.8% D, Sigma–Aldrich) were used as
received. Multinuclear 1H, 13C, and 31P. NMR spectra were recorded
on a Bruker Avance 400 spectrometer (operating at 400.23, 100.61,
and 161.98 MHz, respectively), and a Bruker Avance 500 instru-
ment (operating at 500.15, 125.75 and 202.46 MHz, respectively)
at ambient temperature using CD2Cl2 (c = 0.01 M) or CDCl3
(c = 0.05 M) solutions. 31P{1H} NMR spectra of CD2Cl2 solution of
complex 5 were obtained on a Bruker Avance 300 (operating at
121.49 MHz) in the temperature range 291–200 K. Chemical shifts
(ppm) refer to the residual protic solvent peaks (5.36 ppm for 1H
and 53.45 ppm for 13C), and 85% H3PO4 (for 31P) as external stan-
dards and coupling constants are expressed in hertz (Hz), the band
width at half-height (W1/2) is given in ppm (for 31P{1H} NMR spec-
tra). IR spectra in the region 400–4000 cmꢁ1 for solid samples and
in the region 920–4000 cmꢁ1 for solutions were obtained on a Bru-
ker Tensor 37 FTIR spectrometer. The samples were KBr pellets and
mulls in Nujol as well as 0.01 M solutions in CD2Cl2 in CaF2 cuv-
ettes. The content of C, H, and N was determined on a Carlo Erba
1106 instrument. Melting points were determined in open capil-
lary tubes on a Stanford Research Systems MPA120 EZ-melt auto-
mated melting point apparatus and were not corrected.
ture warmed up to 40 °C, the mixture was stirred without cooling
for 2 h. Next, 30 mL of water was added, the organic layer was sep-
arated and without drying was evaporated to dryness under
reduced pressure and next dried at 80 °C for 4 h at 0.1 mmHg to
give 2.14 g (quantitative) of compound L as a white powder, mp
137–139 °C. Spectral data corresponded to those reported in the
literature [17]. 1H NMR (400.13 MHz, CDCl3) d: 8.05–7.95 (m, 2H,
3
3
H-3,6), 7.70–7.60 (m, 2H, H-4,5), 7.47 (dd, JHH = 7.8, JPH = 12.0,
3
8H, o-CH in Ph-P), 7.39 (t, JHH = 7.8, 4H, p-CH in Ph-P), 7.30–
7.22 (m, 8H, m-CH in Ph-P). 1H{31P} NMR (400.13 MHz, CDCl3) d:
3
3
3
7.99 (dd, JHH = 3.8, JHH = 6.0, 2H, H-3,6), 7.64 (dd, JHH = 3.8,
3JHH = 6.0, 2H, H-4,5), 7.47 (d, JHH = 7.8, 8H, o-CH in Ph-P), 7.39
3
3
3
(t, JHH = 7.8, 4H, p-CH in Ph-P), 7.27 (t, JHH = 7.8, 8H, m-CH in
Ph-P). 13C{1H} NMR (100.61 MHz, CDCl3) d: 136.10 (dd,
1JPC = 98.4, JPC = 7.5, C-1,2), 135.81 (t, JPC = 10.5, C-3.6), 133.01
2
2
1
2
(d, JPC = 108.5, ipso-C in Ph-P), 131.93 (dd, JPC
=
6JPC = 4.0, o-CH
3
4
in Ph-P), 131.23 (s, p-CH in Ph-P), 130.95 (dt, JPC = 8.5, JPC = 6.0,
3
C-4,5), 127.71 (dd, JPC
=
5JPC = 7.0, m-CH in Ph-P). 31P{1H} NMR
(161.97 MHz, CDCl3) d: 31.4.
The reagents—diphenylphospine (Sigma-Aldrich), difluoroben-
zene (Sigma-Aldrich), sodium metal (Sigma-Aldrich), and 30%
H2O2 (reagent grade)—were used. Salts UO2(NO3)2ꢀ6H2O (reagent
grade), Th(NO3)4ꢀ5H2O (pure grade), La(NO3)3ꢀ6H2O (reagent
grade), Eu(NO3)3ꢀ6H2O (pure grade), and Lu(NO3)3ꢀxH2O (Aldrich)
were used without further purification. The water content (x = 3)
in commercial lutetium nitrate was determined experimentally.
The following reagents were used for the preparation of solutions
in the extraction study: bidistilled water, 1,2-dichloroethane
(reagent grade), HNO3 (high purity grade). Solutions for spectral
and extraction studies were prepared by volumetric/gravimetric
method.
4.3. Synthesis of complexes of f-element nitrates
4.3.1. General procedure for the synthesis of complexes 1–5
The complexes 1–5, including those suitable for X-ray diffrac-
tion analysis, were prepared according to a similar procedure, with
a ratio of reagents of 1:1, and 1:2. A solution of UO2(NO3)2ꢀ6H2O or
M(NO3)nꢀxH2O (M = Th, La, Lu; n = 4, 3) in acetonitrile was added
dropwise with stirring to a solution of ligand in acetonitrile. The
yields were 70–90%, but no attempts were made to optimize the
yield for each individual complex.
4.3.1.1. [UO2(L)(NO3)2]ꢀCH3CN, 1. A solution of 0.1147 mmol
(57.6 mg) of UO2(NO3)2ꢀ6H2O in 1 mL of acetonitrile was added
dropwise with stirring to a solution of 0.1147 mmol (54.8 mg) of
ligand L in 2 mL of acetonitrile. The resultant transparent light yel-
low solution was stirred at ambient temperature for 1 h. One day
later, a transparent light yellow crystals of [UO2(L)(NO3)2]ꢀCH3CN
formed, some of them were suitable for X-ray diffraction study.
The crystals were separated by decantation, washed with cold ace-
tonitrile and dried in vacuo (~1 Torr) at 62 °C to give 0.081 g (81%).
Mp (decomp.) > 314 °C. Anal. Calcd. for C30H24N2O10P2UꢀCH3CN: C,
42.07; H, 2.98; N, 4.60%. Found: C, 42.02; H, 2.98; N, 4.38%. IR (nu-
4.2. Ligand synthesis
4.2.1. 1,2-Bis(diphenylphosphinyl)benzene
Sodium foil (0.37 g, 16.1 mmol) was added to a solution of 3.0 g
(16.1 mmol) of diphenylphosphine in 50 mL of anhydrous THF and
stirred for 4 h until complete dissolution. 1,2-Difluorobenzene
(0.734 g, 0.0644 mol, 80% of the theoretical amount) was added
to the resultant brown–yellow solution on cooling to –20 °C. The
mixture was stirred at –20 °C for 1 h and at 20 °C for 24 h. Next,
the mixture was heated for 3 h at 60 °C, cooled, and 5 mL of metha-
nol was added to quench the excess of sodium diphenylphosphide,
yellow color of solution disappeared immediately. Fifty milliliters
of water was added to the solution and the mixture of solvents
was removed under reduced pressure. Water (50 mL) was added
to the residue, the resultant white precipitate was separated by fil-
tration, washed with water (2 ꢂ 50 mL) and methanol (2 ꢂ 5 mL),
and dried under reduced pressure to give 2.79 g (97%) of 1,2-bis
(diphenylphosphinyl)benzene as a white powder, mp 184–185 °C
(lit. mp 183–185 °C [16,33]). 1H NMR (400.13 MHz, CDCl3) d:
jol):
m
max/cmꢁ1 1160vs, 1146sh (P@O), 1517vs, 1490sh (N@O),
1288 s, 1273sh (NO2)as, 1027w (NO2)s, 933 m, 923sh (UO2)as. 1H
NMR (400.13 MHz, CD2Cl2, 0.01 M): d 7.84–7.74 (~2H, m, H-4,5),
7.74–7.64 (~2H, m, H-5,6), 7,64–7.50 (~10H, m, CH in Ph), 7.49–
7.35 (~7H, m, CH in Ph), 7.35–7.15 (~2H, v br s, CH in Ph). The signal
of CH3CN at 2.01 ppm is overlapped with water signal. 13C{1H}
NMR (100.61 MHz, CD2Cl2, 0.01 M): d (italic displays the signals
1
of the minor component) 127.03 (d, JCP = 108, ipso-C in Ph-P),
1
2
127.03 (d, JCP = 110, ipso-C in Ph-P), 129.04 (t, JCP = 6.5, o-CH in
Ph-P), 129.29–129.5 (m, CH in Ph-P), 132.13–132.30 (m, CH in Ph-
7.40–7.32 (m, 2H, H-4,5), 7.30–7.20 (m, 20H, P-C6H5), 7.12–7.08
1
(m, 2H, H-3,6). 13C NMR (100.61 MHz, CDCl3) d: 143.60 (t, JPC
=
3
3
P), 132.38 (t, JCP = 5.5, m-CH in Ph-P), 133.00 (dt, JCP = 6, C-4,5),
2JPC = 10.5, C-1,2), 136.96 (t, JPC
=
4JPC = 2.6, ipso-C in Ph-P),
1
1
2
~133.78 (br dd, JCP = 95, JCP ~ 7, C-1,2), 133.60 (s, p-CH in Ph-P),
2
2
133.98 (t, JPC
= =
3JPC = 3.1, C-3,6), 133.77 (t, JPC 5JPC = 10.0, o-
1
2
133.95 (br s, CH in Ph-P), 134.19 (dd, JCP = 100, JCP = 7.5, C-1,2),
CH in Ph-P), 128.97 (s, C-4,5), 128.23 (s, p-CH in Ph-P), 128.16 (t,
3JPC = 6JPC = 13.0, m-CH in Ph-P). 31P {1H} NMR (161.97 MHz, CDCl3)
d: –14.0.
2
137.47 (t, JCP = 12.5, C-3,6); 31P{1H} NMR (161.98 MHz, CD2Cl2,
0.01 M): d 49.0 (s, W1/2 = 0.24), 46.4 (s, W1/2 = 0.07), integral inten-
sity ratio ~ 1:5.
4.2.2. 1,2-Bis(diphenylphosphoryl)benzene (L)
Hydrogen peroxide (30% solution, 1.27 g, 11.27 mmol) was
added to a solution of 2.0 g (4.48 mmol) of 1,2-bis(diphenylphos-
phinyl)benzene in 30 mL of chloroform with vigorous stirring.
After 10 min, an exotherm was observed so that the reaction mix-
4.3.1.2. [UO2(L)2(NO3)](NO3)ꢀCH3CN, 2. A solution of 0.1111 mmol
(55.8 mg) of UO2(NO3)2ꢀ6H2O in 1.5 mL of acetonitrile was added
dropwise with stirring to a solution of 0.2222 mmol (103.6 mg)
of ligand L in 3 mL of acetonitrile. The resultant transparent light
9

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
1
yellow solution was stirred at ambient temperature for 4 h. One
day later, the transparent solution was concentrated in vacuo (~5
Torr) up to a volume of ~1 mL. A fine-crystalline light yellow pre-
cipitate formed was separated by decantation, washed with cold
acetonitrile and dried in vacuo (~1 Torr) at 62 °C to give 0.115 g
(75%). Mp 296–298 °C. Anal. Calcd. for C60H48N2O12P4Uꢀ0.5CH3CN:
C, 51.40; H, 3.92; N, 2.46%. Found: C, 51.09; H, 3.69; N, 2.21%. IR
132.24 (m, CH in Ph), 132.28 (s, CH in Ph), 135.84 (dd, JCP = 100,
2
2JCP
=
8, C-1,2), 136.83 (t, JCP
=
12, C-3,6). 31P{1H} NMR
(161.98 MHz, CD2Cl2, 0.01 M): d 35.4 (s, W1/2 = 0.05).
4.3.1.5. [Lu(L)2(NO3)3]ꢀ2CH3CN, 5. This compound was synthesized
according to the general method similar to preparation of com-
plex 2, from 0.0758 mmol (31.5 mg) of Lu(NO3)3ꢀ3H2O and
0.1517 mmol (72.6 mg) of L. The mixture was concentrated in
vacuo (~5 Torr) to a volume of ~ 0.7 mL. Transparent crystals of
5 formed, some of them were suitable for X-ray diffraction study.
The crystals were separated by decantation, washed with cold
acetonitrile, and dried in vacuo (~1 Torr) at 62 °C to give
(KBr disk, nujol): m
max/cmꢁ1 1142vs, 1149sh (P@O), 1470 m (KBr
disk), 1344 m, 1296 m, ~1020w, 918 m, 925sh (UO2)as. 1H NMR
(400.13 MHz, CD2Cl2, 0.01 M): d 7.82–7.72 (~4H, m, H-4,5), 7.72–
7.63 (~2H, m, H-3,6), 7.64–7.53 (~14H, m, CH in Ph), 7.53–7.45
(~1H, CH in Ph), 7.45–7.35 (~10H, m, CH in Ph), 7.35–7.20 (~16H,
v br s, CH in Ph), 7.15 (~1H, v br s, CH in Ph). 2.01 (s, CH3CN). 13C
{1H} NMR (100.61 MHz, CD2Cl2, 0.01 M): d (italic displays the sig-
nals of the minor component) 127.86 (d, 1JCP = 112, ipso-C in Ph-P),
0.065 g (65%) of complex 5. Mp 181–183 °C. Anal. Calcd. for C60
-
H
48LuN3O13P4ꢀ0.5CH3CNꢀ0.5H2O: C, 54.37; H, 3.78; N, 3.64. Found:
C, 54.39; H, 3.97; N, 3.84%. IR (nujol):
m
max/cmꢁ1 1167 s, 1145 s
1
(P@O), ~1500 m, 1340 m, 1305 m, 1027w, 2249w (C„N),
3390w (H2O). H NMR (400.13 MHz, CD2Cl2, 0.01 M): d 7.82–
128.04 (d, JCP = 111, ipso-C in Ph-P), ~128.8 m (CH in Ph-P), 128.99
2
(t, JCP = 7, o-CH in Ph-P), ~132.0 br m (CH in Ph-P), 132.33 (t,
3JCP = 5, m-CH in Ph-P), 133.08–132.97 (m, C-4,5), 133.49 (s, p-CH
7.92 (4H, v br s, H-4,5), 7.55–7.49 (8H, m, p-CH in Ph-P), 7.50–
1
2
7.38 (4H, br m, H-3,6), 7.29–7.20 (32H, br m, CH in Ph),. 2.01
in Ph-P), 134.04 (dd, JCP = 100, JCP = 7, C-1,2), 134.21(dd,
(s, CH3CN). 13C{1H} NMR (100.61 MHz, CD2Cl2, 0.01 M):
d
1JCP = 100, JCP = 8, C-1,2), 137.32 s (CH in Ph-P), 137.57 (t,
2
1
2
2JCP = 12.5, C-3,6); 31P{1H} NMR (161.98 MHz, CD2Cl2, 0.01 M): d
46.5 (s, W1/2 = 0.05), 46.3 (s, W1/2 = 0.02), integral intensity ratio ~ 5:
1. Transparent light yellow crystals of [UO2(L)2(NO3)2]ꢀCH3CN,
some of them suitable for X-ray diffraction study were grown from
acetonitrile.
127.29 (d, JCP = 112, ipso-C in Ph-P), 129.04 (t, JCP = 6.5, o-CH
3
in Ph-P), 131.88 (t. JCP = 5.5, m-CH in Ph-P), 133.4–133.0 (m,
1
2
C-4,5), 133.56 (s, p-CH in Ph-P), 134.22 (dd, JCP = 100, JCP = 7,
C-1,2), 137.86 (t, 2JCP = 12, C-3,6). 31P{1H} NMR (161.98 MHz, CD2-
Cl2, 0.01 M): d 41.9 (s, W1/2 = 0.05).
4.3.1.3. [Th(L)2(NO3)4]ꢀCH3CNꢀH2O, 3. A solution of 0.0397
g
4.3.2. Procedure for the preparation of model solution with metal:
ligand ratios of 1:3
To prepare solution with metal:ligand molar ratio of 1:3, a cal-
culated amount of ligand L was added to a 0.01 M solution of com-
plex 4 in CD3CN.
(0.0696 mmol) of Th(NO3)4ꢀ5H2O in 1 mL of acetonitrile was added
dropwise with stirring to a solution of 0.0666 g (0.2222 mmol) of
ligand L in 3 mL of acetonitrile. The resultant transparent solution
was stirred at ambient temperature for 4 h. After two days, the
solution was evaporated to dryness under reduced pressure to give
a white solid. The residue was dried in vacuo (~1 Torr) at 62 °C to
give 0.085 g (85%) of the title compound. Mp 178–180 °C. Anal.
Calcd. for C60H48N4O16P4ThꢀCH3CNꢀH2O: C, 49.78; H, 3.57; N,
4.4. X-ray crystallography
4.68%. Found: C, 49.54; H, 3.33; N, 4.11%. IR (nujol): m
max/cmꢁ1
Single crystals of 1, 5 were obtained from reaction mixture,
single crystals of 2 were grown from MeCN. The intensities of
reflections were measured with a Bruker Apex II (2) or a Bruker
D8 Quest (1, 5) CCD diffractometer using graphite monochro-
1136 s (P@O), 1512 m (N@O), 1288 m (NO2)as, 1023w (NO2)s. 1H
NMR (500.13 MHz, CD2Cl2, 0.01 M): d 7.80–7.77 (4H, m, H-4,5),
7.49 (8H, dt, p-CH in Ph-P), 7.46–7.42 (4H, m, H-3,6), 7.40–7.36
mated MoK
a radiation (k = 0.71073 Å) at 120 and 296 K,
(16H, m, CH in Ph), 7.28–7.24 (16H, m, CH in Ph). 2.01 (s, CH3CN).
13C{1H} NMR (125.75 MHz, CD2Cl2, 0.01 M):
d 126.43 (d,
respectively. The structures were solved by the SHELXT method
[34] and refined by full-matrix least squares against F2. Non-
hydrogen atoms were refined anisotropically. The positions of
all hydrogen atoms were calculated, and were included in the
refinement by the riding model with Uiso(H) = 1.5Ueq(X) for
methyl groups, and 1.2Ueq(C) for the other atoms. All calcula-
tions were made using the SHELXL2014 [35] and OLEX2 [36]
program packages. Crystal parameters and refinement details
are listed in Table 5. CCDC 2039977–2039979 for complexes
1JCP = 112.5, ipso-C in Ph-P), 129.27–129.10 (m, CH in Ph),
132.26–132.10 (m, CH in Ph), 133.22–133.04 (m, C-4,5), 133.21
1
2
(dd, JCP = 101.2, JCP = 7.5, C-1,2), 133.87 (s, p-CH in Ph-P),
137.84 (t, JCP = 12.5, C-3,6). 31P{1H} NMR (202.46 MHz, CD2Cl2,
2
0.01 M): d 44.9 (s, W1/2 = 0.01).
4.3.1.4. [La(L)2(NO3)3]ꢀ0.5CH3CNꢀ1.5H2O, 4. This compound was
synthesized according to the general method similar to the prepa-
ration of complex 2 from 0.0758 mmol (32.8 mg) of La(NO3)3ꢀ6H2O
and 0.1517 mmol (72.6 mg) of L. The mixture was concentrated in
vacuo (~5 Torr) to a volume of ~0.7 mL. The fine-crystalline white
precipitate formed was filtered, washed by cold acetonitrile, and
dried in vacuo (~1 Torr) at 62 °C to give 0.069 g (70.1%) of complex
1, 2,
5 contain the supplementary crystallographic data for
these compounds.
4.5. Computational details
Geometry optimization of uranyl complex [UO2L(NO3)2] and
cation of bisligand complex [UO2L2(NO3)]+ was done with
GAUSSIAN 09 [37] software suite on DFT level of theory. The
hybrid PBE0 [38] functional and Stuttgart MWB60 basis set
[39] for U atom and 6-311+G** [40] basis set for other atoms
were utilized. Topological analysis of electron density according
to Bader’s ‘‘Atoms in Molecules’’ theory (AIM) [41] was per-
formed in AIMAll [42] program, in which connection ECP
MWB60 basis set for U atom was changed to all-electron basis
4. Mp 218–221 °C. Anal. Calcd. for
C
60H48LaN3O13P4ꢀ0.5CH3-
CNꢀ1.5H2O: C, 55.11; H, 3.98; N, 3.69%. Found: C, 55.17; H, 4.04;
N, 3.70%. IR (nujol):
m
max/cmꢁ1 1178vs (P@O), 1317 s, 1295sh,
1936w, 1031sh. 1H NMR (400.13 MHz, CD2Cl2, 0.01 M): d 7.60–
7.52 (~4H, m, H-4,5), 7.5 2–7.40 (~15H, m, CH in Ph), 7.40–7.20
(~10H, m, CH in Ph), 7.25–7.0 5 (~14H, CH in Ph). 2.01 (s, CH3CN).
No signal of H-3,6 nuclei was observed. 13C{1H} NMR (100.61 MHz,
CD2Cl2, 0.01 M): d 128.52–128.36 (m, CH in Ph), 129.44 (d,
1JCP = 110, ipso-C in Ph-P), 131.61–131.39 (m, C-4,5), 132.23–
set [43]. Interaction energies of
p-stacking and CAH. . .p
10

A.G. Matveeva, O.I. Artyushin, M.P. Pasechnik et al.
Polyhedron 198 (2021) 115085
Table 5
Crystallographic data and refinement parameters for [UO2L(NO3)2] MeCN (1), [UO2L2(NO3)](NO3)ꢀMeCN (2), and [LuL2(NO3)2](NO3)ꢀ2MeCN (5).
1
2
5
Empirical formula
Fw
C
32H27N3O10P2U
C62H50N3O12P4U
1390.96
C64H48LuN5O13P4
1393.92
913.53
Color, habit
Crystal size (mm)
Crystal system
Space group
a (Å)
Yellow, prism
0.46 ꢂ 0.20 ꢂ 0.13
Monoclinic
P21/n
9.5720(1)
28.5901(4)
12.8343(2)
91.1199(6)
3511.62(8)
4
Yellow, prism
0.38 ꢂ 0.12 ꢂ 0.12
Monoclinic
C2/c
Colorless, prism
0.25 ꢂ 0.21 ꢂ 0.11
Monoclinic
C2/c
16.4529(3)
15.4128(3)
25.0928(4)
96.5138(7)
6322.1(2)
31.167(3)
b (Å)
c (Å)
18.9090(15)
21.5536(17)
107.863(2)
12089.9(17)
8
2.854
1.528
5528
b (°)
V (Å3)
Z
l
4
(cmꢁ1
)
4.771
1.728
1768
1.729
1.385
2808
Dcalc (g cmꢁ3
F(000)
)
No. of measured, independent and observed [I > 2
r
(I)] reflections
64634, 13986, 10.,567
0.0426
0.0335, 0.0694, 1.1
1.17, ꢁ1.12
82423, 18484, 11.,941
0.0924
0.0577, 0.1615, 1.0
2.74, ꢁ2.44
62829, 13920, 11.,348
0.0455
0.0409, 0.1082, 1.0
2.00, ꢁ0.94
Rint
R[F2 > 2
r
(F2)], wR(F2), S
qmin (e Åꢁ3
D
qmax
,
D
)
contacts were estimated with Espinosa’s correlation scheme
Acknowledgement
Econt = ꢁ1/2V(r) [44].
This work was financially supported by the Russian Science
Foundation (project no. 20–13–00329). Spectral studies were car-
ried out with the financial support from the Ministry of Science
and Higher Education of the Russian Federation using the equip-
ment of the Center for Molecular Structure Studies, INEOS RAS.
4.6. Extraction of f-elements
1,2-Dichloroethane (DCE) of reagent grade was used without
additional purification as the organic solvent. Solutions of extrac-
tants were prepared from accurately weighed samples. The initial
aqueous solutions of lanthanides(III), U(VI), and Th(IV) were pre-
pared by dissolving the respective nitrates in water followed by
the addition of HNO3. The initial concentrations of metal ions were
2 ꢀ 10–6 M, the concentration of HNO3 was 2 M. The extraction
experiments were performed in test tubes equipped sealing plugs
at room temperature and 1:1 vol ratio of organic and aqueous
phases. The phases were contacted in a rotary mixer at rate of
60 rpm for 1 h, this time being sufficient to reach constant values
of the distribution ratio (DM).
The concentration of Ln(III), U(VI) and Th(IV) in the initial and
equilibrated aqueous solutions was determined by mass spectrom-
etry with inductively coupled plasma ionization of samples (ICP-
MS), using a Thermo Elemental X-7 mass spectrometer according
to a published method [45]. The content of elements in the organic
phase was obtained from the material balance. The distribution
ratios for the elements were calculated as ratios of the equilibrium
concentration in the organic and aqueous phases (DM = [Morg]/
[Maq]). Triple experiments showed that the reproducibility of the
D was generally within 5%.
Appendix A. Supplementary data
CCDC 2039977 (1), 2039978 (2) and 2039979 (5) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data to this article can be found online at https://doi.org/10.1016/j.
poly.2021.115085.
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Anna G. Matveeva: Conceptualization, Methodology, Writing -
review & editing. Oleg I. Artyushin: Data curation. Margarita P.
Pasechnik: Data curation. Adam I. Stash: Data curation. Anna V.
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12