Neodymium, erbium, and europium complexes with 1,6-bis(diphenylphosphoryl)-2,5-dioxahexane (L): The crystal structure of [Nd2(NO3)6L3]

Article abstract of DOI:10.1134/S0036023615070049

Solid complexes M(NO₃)₃·1.5L (M = Nd, Er, Eu; L is 1,6-bis(diphenylphosphoryl)-2,5-dioxahexane) have been synthesized. A new, convenient method of synthesis of L has been suggested. The crystal structure of [Nd₂(NO₃

Full text of DOI:10.1134/S0036023615070049

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2015, Vol. 60, No. 7, pp. 843–847. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © V.E. Baulin, I.S. Ivanova, I.N. Polyakova, E.N. Pyatova, V.N. Rychkov, E.V. Kirillov, S.V. Kirillov, A.Yu. Tsivadze, 2015, published in Zhurnal Neorganicheskoi
Khimii, 2015, Vol. 60, No. 7, pp. 929–934.
Neodymium, Erbium, and Europium Complexes
with 1,6ꢀBis(diphenylphosphoryl)ꢀ2,5ꢀdioxahexane (L):
The Crystal Structure of [Nd2(NO3)6L3]
,
c
V. E. Baulina , I. S. Ivanovab, I. N. Polyakovab, E. N. Pyatovab, V. N. Rychkovd,
E. V. Kirillovd, S. V. Kirillovd, and A. Yu. Tsivadzea
aFrumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
bKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
cInstitute of Physiologically Active Compounds, Russian Academy of Sciences,
Chernogolovka, Moscow oblast, 142432 Russia
dUral Federal University Named after the First President of Russia B.N. Yeltsin,
ul. Mira 19, Yekaterinburg, 620002 Russia
eꢀmail: mager1988@gmail.com
Received December 15, 2014
Abstract—Solid complexes M(NO3)3 ⋅ 1.5L (M = Nd, Er, Eu; L is 1,6ꢀbis(diphenylphosphoryl)ꢀ2,5ꢀdioxaꢀ
hexane) have been synthesized. A new, convenient method of synthesis of L has been suggested. The crystal
structure of [Nd2(NO3)6L3] has been determined by singleꢀcrystal Xꢀray diffraction. The nonacoordination
environments of the Nd(1) and Nd(2) atoms are composed each of six O atoms of bidentate nitrate ions and
three phosphoryl O atoms of the L molecules (av. Nd–O, 2.543 and 2.374 Å, respectively). Two independent
L molecules act as bridges linking the Nd atoms to form centrosymmetric tetramers [LꢀNd(NO3)3ꢀLꢀ
Nd(NO3)3ꢀL2ꢀNd(NO3)3ꢀLꢀNd(NO3)3L]. The third L molecule is disordered over two positions with site
occupancy factors of 0.602(4) and 0.398(4) so that most of the molecules chelate the terminal Nd atoms in
the tetramer, and the other molecules combine tetramers into longer associates. On the basis of elemental
analysis data and IR spectra, it has been assumed that the Er and Eu complexes have the same structure as
[Nd2(NO3)6L3].
DOI: 10.1134/S0036023615070049
As known, the most common technique for indusꢀ obtained under milder synthetic conditions—from
neutral solutions [5].
trial isolation of such an important raw material as rare
earth elements (REEs) is extraction. Polydentate neuꢀ
tral organophosphorus compounds have long been
studied as extractants for a wide range of REEs [1]. It
has been shown that an equimolar mixture of
oligo(ethylene glycol) bis(diphenylphosphorylmethyl)
ethers with the Hꢀform of chlorinated cobalt(III)
dicarbollide in solutions of polar diluents are efficient
REE extractants [2]. The structures of the REE
The cation exchange extraction of Eu(III) and
Sr(II) from aqueous nitrate solutions with diphenylꢀ
diphosphine dioxides containing a methyl, ethyl, or
poly(ethylene glycol) bridge between the phosphorus
atoms has been studied [6]. The IR spectra have proꢀ
vided evidence that most of the formed complexes
have a chelate structure and that, when taken in high
concentration, the ligand with the poly(ethylene glyꢀ
extraction complexes have been little studied. The col) bridge can act as a monodentate ligand. Studying
extraction of REEs with 1ꢀ(methoxydiphenylphosꢀ lanthanide complexes in solutions is a challenging task
phoryl)ꢀ2ꢀdiphenylphosphorylꢀ4ꢀethylbenzene (LMP)
has been studied [3]. The crystal structure of isostrucꢀ
tural neodymium and ytterbium complexes with LMP
isolated from an extraction solution has been deterꢀ
mined by Xꢀray crystallography, and the structures of
free LMP and its adduct with water and nitric acid have
been determined [4]. The same structure of the comꢀ
plex cation has also been found in the Er compounds
with LMP and 1ꢀ(methoxydiphenylphosphoryl)ꢀ2ꢀ
since it requires the use of several methods; it should
be noted that NMR and EPR methods are of limited
use because most of lanthanide cations exhibit paraꢀ
magnetic properties. Xꢀray crystallography enables the
unambiguous determination of the structure of crysꢀ
talline complexes.
Here, were report the synthesis of the M(NO3)3
.5L complexes (L is 1,6ꢀbis(diphenylphosphoryl)ꢀ
2,5ꢀdioxahexane; M = Nd ( ), Er (II), Eu (III)) and
determined by sinꢀ
·
1
I
diphenylphosphorylbezene, their crystals being the crystal structure of complex
I
843

844
BAULIN et al.
gleꢀcrystal Xꢀray diffraction and suggest a new effiꢀ in [8]. A mixture of KOH and K2CO3 powders was
cient (81%) oneꢀstage procedure for synthesis of L.
used as the solid phase, and the second phase was a
solution of diphenylphosphinic acid and 1,2ꢀbis(chloꢀ
romethoxy)ethane in benzene. The synthesis was catꢀ
alyzed by 18ꢀcrownꢀ6 as a phaseꢀtransfer catalyst. The
yield of L was only 33%.
EXPERIMENTAL
First oligo(ethylene glycol) bis(diphenylphosphoꢀ
rylmethyl) ethers have been synthesized almost
30 years ago [7]. Relatively recently, 1,6ꢀbis(dipheꢀ
nylphosphoryl)ꢀ2,5ꢀdioxahexane (L) have been synꢀ
thesized through alkylation of lithium glycolates with
diphenylchloromethylphosphine oxide. Lithium glyꢀ
colates have been produced in a separate stage by
treating ethylene glycol with butyllithium [8]. The
synthesis of this ether with the use of a nonꢀaqueous
In the present work, compound L was synthesized
by alkylation of diphenyloxymethylphosphine oxide
with ethylene glycol ditosylate in dry dioxane at
100°C in the presence of anhydrous Cs2CO3 as the
base (Scheme 1). Thinꢀlayer chromatography and
31P NMR have shown that alkylation of ethyl glycol
with diphenylphosphorylmethanol tosylate does not
twoꢀphase liquid/solid system has also been described lead to the formation of L.
OH
1. Cs CO
2
2. TsOCH CH OTs
3
O
2
2
P
Dioxane, 100
°С, 10 h
Ph Ph
O
P
O
P
O
O
OH
1. Cs CO
2
3
2. Ph P(O)CH OTs
Ph Ph Ph Ph
2
2
Dioxane, 100°С, 10 h
L
OH
Scheme 1. Synthesis of 1,6ꢀbis(diphenylphosphoryl)ꢀ2,5ꢀdioxahexane (L).
The synthesis with the use of anhydrous cesium raphy on a column with silica gel. The yield of L was
carbonate was carried out in a dry argon atmosphere. 19.8 g (81%), mp = 163–165°С (methyl ethyl ketone).
The course of reaction and purity of the target comꢀ
pound were monitored by thinꢀlayer chromatography
on Silufol plates. The chromatograms were developed
with iodine vapor. For column chromatography, silica
For C30H32O5P2 anal. calcd. (%): C, 68.57;
H, 5.75; P, 12.63.
Found (%): C, 68.60; H, 5.73; P, 12.43.
1Н NMR (CDCl3,
СН2СН2О), 4.23 (d, 4H, JH–H = 7.0 Hz,
2ОСН2Р(О)), 7.44 (m, 12H, ArꢀH), 7.77 (m, 8H,
δ
, ppm): 3.71 (s, 4H,
gel L (particle size, 100–160
was accomplished with СHCl3 and a СHCl3–
µ
m) was used. Elution
2
iꢀPrOH
(20 : 1) mixture. The yield of the target product is given
for the product with the melting point that differs from
the melting point of an analytical sample by no more
than 5 K. The melting temperature was measured with
a shortꢀrange Anschutzꢀtype thermometer. An emerꢀ
Arꢀ
H).
31P NMR (CDCl3,
δ
, ppm): 27.92.
Complexes I–III as fine crystalline precipitates
were obtained from a mixture of ethanol solutions of
the corresponding salt and the ligand (M : L = 1 : 2) on
slow evaporation of the solvent. The precipitates were
filtered off, washed with ethanol, and dried in air. Only
the crystals of the Nd complexes turned out to be suitꢀ
able for Xꢀray crystallography.
1
gent stem correction was not applied. H and
31P NMR spectra were recorded on a Bruker CXPꢀ200
spectrometer. The chemical shifts were referenced to
internal TMS and external 85% Н3РО4, respectively.
Synthesis of L. Diphenylphosphorylmethanol
(23.2 g, 100.0 mmol) [9] and ethylene glycol tosylate
(18.5 g, 50.0 mmol) [10] were added to a suspension of
finely ground anhydrous Cs2CO3 (32.6 g, 100.0 mmol)
in 80 mL of dry dioxane. The mixture was stirred for
For I anal. calcd. (%): C, 47.32; H, 3.94; N, 3.94.
Found (%): C, 47.93; H, 4.28; N, 3.98.
For II anal. calcd. (%): C, 46.32; H, 3.86: N, 3.86.
Found (%): C, 45.95; H, 4.26; N, 3.41.
For III anal. calcd. (%): C, 47.01; H, 3.92; N, 3.92.
Found (%): C, 46.95; H, 4.55; N, 3.68.
8 h at 95 5
100 mL of HCl (1 : 2) was added to the residue, and
extraction with chloroform ( 75 mL) was carried out.
The extract was washed with HCl (1 : 2) ( 50 mL),
water (
resulting product was purified by column chromatogꢀ range 4000–400 cm–1.
°С and concentrated in a vacuum. Then,
3
×
5
×
IR absorption spectra were recorded as mineral oil
5
×
50 mL) and evaporated in a vacuum. The mulls on a Bruker Vertex 70 spectrophotometer in the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 7 2015

NEODYMIUM, ERBIUM, AND EUROPIUM COMPLEXES
845
Crystal data, parameters of data collection, and characterꢀ
istics of structure refinement for [Nd2(NO3)6L3]
Xꢀray crystallography. The set of diffraction reflecꢀ
tions from a crystal of was collected on an automated
I
Bruker SMART APEX2 diffractometer at the Shared
Facility Center of the Institute of General and Inorganic
Chemistry, RAS. The structure was solved by direct
methods. The hydrogen atoms were introduced in calcuꢀ
lated positions. In one of the ligand molecules, the ethylꢀ
ene glycol moiety is disordered over two orientations
(C(14B)C(15B)O(3B) and C(14D)C(15D)O(3D))
with site occupancy factors of 0.602(4) and 0.398(4).
Nonꢀhydrogen atoms were refined in the anisotropic
approximation, except the C(14D) and C(15D) atoms
refined isotropically. The hydrogen atoms were refined
Parameter
Value
Empirical formula
FW
C84H84N6Nd2O30P6
2131.88
T,
Radiation,
Space group,
K
174(2)
λ
, Å
MoK , 0.71073
α
Z
P
1, 2
as riding on their parent atoms with
corresponding C atom.
The set of reflections was collected and processed
with the use of the APEX2, SAINT, and SADABS proꢀ
grams [11]. Structure solution and refinement were
performed with the SHELXSꢀ97 and SHELXLꢀ2013
[12] program packages, respectively.
Uiso = 1.2Ueq of the
a
, Å
, Å
15.278(3)
16.103(4)
18.821(4)
93.940(30
92.926(4)
96.975(3)
4576.9(17)
1.547
b
c
, Å
, deg
, deg
, deg
, Å3
α
Selected crystal data and experimental and refineꢀ
β
ment details for structure
I
are presented in the table.
γ
The crystallographic data for
I
were deposited with
the Cambridge Crystallographic Data Centre (CCDC
no. 1036221).
V
ρcalcd, g/cm3
μMo, mm–1
RESULTS AND DISCUSSION
1.310
A
fragment of the crystal structure of
Tmin
(000)
Crystal size, mm
range, deg
,
Tmax
0.6535, 0.7462
2160
[
Nd2(NO3)6L3] is shown in the figure. The asymmetric
−
unit contains two Nd atoms, six
groups, and three
NO3
F
L molecules (A, B, and C). The environments of the
Nd(1) and Nd(2) atoms consist each of six O atoms of
three bidentate nitrate ions and three O phosphoryl
atoms of the L molecules. The coordination polyhedra
of Nd atoms can be presented as octahedra with split
0.24
×
0.10 × 0.06
θ
2.173–31.362
Number of reflections:
measured
NO3−
vertices occupied by the oxygen atoms of the
57378
28792 [0.0423]
19033
groups. The “octahedra” of both Nd atoms are meridꢀ
ional isomers. The Nd–O bond lengths are within
2.359(2)–2.585(3) Å. The Nd–O(P) bonds are shorter
than Nd–O(N) (av. 2.374 and 2.543 Å, respectively).
unique (
with > 2
1, wR2 for No
1, wR2 for
N
) [Rint
]
I
σ
(
I) (No
)
The independent molecules of podand A, B, and C
have different functions. Pairs of molecules C link the
Nd(2) atoms into centrosymmetric dimers
[Nd(2)(NO3)3L2]2. Molecule A links the Nd(1) and
Nd(2) atoms, thus increasing the dimer to the tetꢀ
ramer. Both phosphoryl oxygen atoms of molecule B
coordinate the Nd(1) atom. The C(14)–C(15)–O(3)
moiety of molecule B is disordered so that the moleꢀ
cule either closes an 11ꢀmembered chelate ring or
links two Nd(1) atoms, just like molecule C links the
Nd(2) atoms. Among disordered molecules B, the
number of chelating molecules is one and a half times
larger than the number of bridging molecules. The
crystal surely contains tetramers (figure) and, with
high probability, octamers. Formation of longer oligoꢀ
mers with the number of Nd atoms multiple of four is
theoretically possible.
R
0.0505, 0.1010
0.0909, 0.1151
1.025
R
N
S
Δρmax
/
Δρmin, e/Å3
1.171/–1.450
Previously,
[Er(NO3)3(Lig)(H2O)] (IV
logue of phosphoryl podand L with a longer
(CH2CH2O)3CH2CH2– chain between the phosꢀ
the
structure
of
the
)
complex (Lig is an anaꢀ
⎯
phoryl groups has been studied [13]. Like in other Nd
complexes, the nitrate ions in structure IV occupy the
split vertices in the mer isomer of the “octahedron.”
The Lig molecule chelates the Eu atom through the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 7 2015

846
BAULIN et al.
C(7)
P(1)
A
C(13)
O(2)
C(1)
O(1)
Nd(1)
C(13)
O(2)
C(14)
C(7)
P(1)
C(14)
O(1)
C(15)
C(15)
O(3)
C(16)
P(2)
O(3)
O(4)
C(1)
C(16)
P(2)
C(17)
C(23)
O(4)
Nd(2)
C(14)
C(16)
P(2)
O(4)
O(2)
C(1)
B
O(1)
C(23)
C(15)
O(3)
C(23)
C(17)
C(13)
P(1)
C(7)
C
Structure of the tetramer complex in the crystal of [Nd (NO ) L ]. For simplicity, the phenyl carbon atoms other than those
2
3 6 3
directly bonded to the phosphorus atoms are omitted.
phosphoryl O atoms, closing a 16ꢀmembered chelate L molecules, structure I studied in this work is topoꢀ
logically closer to the dimeric structures.
ring. As distinct from ligand L in Nd complexes, the
Lig molecule in structure IV occupies the trans vertices
of the Er “octahedron,” which evidently creates steric
hindrances to coordination of one more O atom of the
diphenylphosphoryl group. The ninth coordination
site is occupied by a water molecule forming intramoꢀ
lecular hydrogen bonds to the ether O atoms of the Lig
molecule.
Conclusions concerning the structure of comꢀ
plexes II and III have been drawn from elemental
analysis and IR spectroscopy data.
Basic vibrational frequencies in the spectra of L
and complexes I–III have been assigned using the
interpretation of vibrational spectra of complexes with
phosphorylꢀcontaining podands reported in [17–19].
Inasmuch as complexation leads to the largest changes
in stretching vibration frequencies of donor groups
involved in formation of coordination bonds, we
mainly dwell on the vibrational frequencies of P=O
and COC groups.
The phosphoryl stretching vibration, whose freꢀ
quency is determined by the electronegativity of the
substituent at the phosphorus atom, is observed in the
IR spectrum of L at ~1180 cm–1 as a strong and narrow
band. This frequency is somewhat lower than in the
spectra of Ph3P=O, phosphoryl podands with the
diphenylphosphoryl group in the orthoꢀposition of
the benzene ring (1195 cm–1) [17–19] and in the specꢀ
trum of Lig (1185 cm–1) [13].
Since the ether O atoms of the L molecules in
structure
I are not involved in coordination of the Nd
atom, the Ph2(O)P–(CH2)n–P(O)Ph2 molecules (Ln
)
in which the phosphoryl groups are linked by an alkyl
chain can be treated as analogues of the L podand. The
structures of lanthanide complexes with such ligands
in which the number of methylene groups n = 1 [14],
2 [15], and 4 [16] are known. The L1 ligand with the
shortest chain forms chelate complexes with different
NO3 : L ratios in the coordination sphere, in particuꢀ
lar, [Nd(NO ) 1 (H2O)]NO3
2H2O. The L2 ligand
3 2L2
⋅
with the ethyl spacer forms layered coordination
polymers of composition [Ln2(NO3)6 L23 ] with Pr,
According to [17, 18], the νas(СОС) bands sensiꢀ
tive to the conformation of the ethylene glycol units in
the podands are observed in the range 1100–1160 cm–1
in their IR spectra. The benzene ring vibration band is
observed in the same range (1127 cm–1 in the IR specꢀ
trum of Ph3P=O). The spectrum of L shows two bands
of roughly the same intensity in the νas(СОС) region:
at 1123 and 1090 cm–1 with a shoulder at 1005 cm–1.
Nd, Sm, and Dy. These polymers have been isolated
as solvates with dichloroethane for Ln = Pr and Nd
and methanol for Ln = Sm and in the unsolvated
form for Ln = Nd and Dy. With the same metals,
ligand L4 forms isostructural dimeric complexes
[L4Ln(NO3)3L4Ln(NO3)3L4]
1.5CH3OH, in which
⋅
there is one bridging molecule per two chelating molꢀ
ecules. The Lu and Dy complexes of composition
In the IR spectrum of L in the range 800–1000 cm–1,
conformationally sensitive composite stretching–
[Ln2(NO3)6L23
] ⋅ CH3OH have an analogous structure.
Owing to the combination of chelating and bridging bending vibrations
ν(СО) +
ρ
(СН2) + (СС) give rise
ν
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 7 2015

NEODYMIUM, ERBIUM, AND EUROPIUM COMPLEXES
847
to three moderate bands at 887, 872, and 831 cm–1 and Nd atoms multiple of four. In the structures of Er and
to a weak band at ~943 cm–1.
Eu compounds, association of complexes into oligoꢀ
mers with another number of metal atoms is possible.
Complexation leads to a noticeable change in the
IR spectrum of L. The spectra of complexes I–III are
identical in the entire spectral range and are essentially
simpler than the spectrum of L. The spectrum of the
free podand shows sharp and wellꢀresolved bands,
while, in the spectra of the complexes, these bands are
broad and smooth, which is typical of compounds with
polymeric structure.
ACKNOWLEDGMENTS
This work was supported by the Ministry of Educaꢀ
tion and Science of the Russian Federation in the
framework of grant agreement no. 14.581.21.0002,
September 29, 2014, of the Federal Target Program
“Research and Development in the Top Priority
Fields of Russia’s Science and Technology Complex
for 2014–2020.”
The coordination of the phosphoryl oxygen atoms
in
I–III leads to a decrease in the (Р=О) frequency
ν
by ~20 cm–1, which is evidence that these atoms are
involved in coordination of the metal cation. In the
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(NO3) band is observed
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:
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The coordination polyhedra of the metal atoms are
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[Nd2(NO3)6L3] contains oligomers with the number of
Translated by G. Kirakosyan
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 7 2015