2,4-Bis(diphenylphosphorylmethyl)mesitylene complexes with neodymium nitrate: Synthesis, structure, and dynamic behavior in solutions

Full text of DOI:10.1134/S0012500807040052

ISSN 0012-5008, Doklady Chemistry, 2007, Vol. 413, Part 2, pp. 95–99. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © A.G. Matveeva, A.S. Peregudov, E.I. Matrosov, Z.A. Starikova, G.I. Timofeeva, S.V. Matveev, G.V. Bodrin, E.E. Nifant’ev, 2007, published in Doklady
Akademii Nauk, 2007, Vol. 413, No. 6, pp. 771–775.
CHEMISTRY
2
,4-Bis(diphenylphosphorylmethyl)mesitylene Complexes
with Neodymium Nitrate: Synthesis, Structure,
and Dynamic Behavior in Solutions
A. G. Matveeva, A. S. Peregudov, E. I. Matrosov, Z. A. Starikova, G. I. Timofeeva,
S. V. Matveev, G. V. Bodrin, and Corresponding Member of the RAS E. E. Nifant’ev
Received June 5, 2006
DOI: 10.1134/S0012500807040052
An important problem in the chemistry of organo-
Ligands of this type are fairly promising reagents
phosphorus compounds is the design of new bis(phos- for separation of transplutonium and rare-earth ele-
phine oxides). Currently, this problem is being success- ments by extraction from aqueous nitric acid solu-
fully solved; new effective ligands of interest for tions [1].
nuclear power engineering and medicine have been
obtained. A key aspect of the studies and applications
of new ligands in chemical and biological processes
The stable mononuclear complexes [Nd(L)(NO ) ] ·
3
3
H O (I) and [Nd(L) (NO ) ] · 4H O (II) with the same
2
2
3 3
2
chelation mode of the ligand and the bidentate coordi-
nation of the nitrato groups were isolated in a pure state.
Their vibrational spectra were in good agreement with
the proposed structures.
(
homogeneous catalysis, liquid extraction, biological
activity mechanisms, etc.) is the structure and conver-
sions of their metal complexes in solutions. Among
other metal complexes, structures of lanthanide com-
plexes remain an important and challenging issue.
Whereas the structures of complexes in the crystalline
state can be unambiguously determined by X-ray crys-
tallography, studies of lanthanide complexes in solu-
tions require the use of several methods, the scope of
NMR and EPR being limited due to the specific para-
magnetic properties of most lanthanide cations and to
the lability of complexes.
In the IR spectra of solid complexes I and II, the
–1
P=O band is bathochromically shifted to 1145 cm ,
–1
while the band due to free P=O groups (1195 cm ) is
missing. The spectra also contain strong bands at 1500
–1
(
1480), 1300 (1310), and 1040 (1032) cm for the
nitrate groups coordinated as bidentate ligands, while
the band for free NO groups is missing [2]. In the OH
3
–
1
vibration range (3400–3500 cm ), a broad band for
outer-sphere water molecules is present. The strong line
at 1027 cm in the Raman spectra of the complexes
also supports the bidentate coordination of the nitrate
groups.
In this paper, we report the results of studies on the
structures of neodymium nitrate complexes with a new
neutral diphosphoryl ligand L in the solid state and in
–
1
3
1
solutions and demonstrate new possibilities of using P
NMR spectroscopy for studying ionic complexation
equilibria.
The structure of [Nd(L)(NO ) Me CO], obtained by
3 3
2
isothermal evaporation of a solution of I in a CD CN–
The dioxide L was prepared by theArbuzov reaction
3
Me CO mixture (20 : 1), was determined by X-ray dif-
of 2,4-bis(bromomethyl)mesitylene with Ph POMe.
2
2
fraction.
The
3
structure
of
the
neutral
Me
[
Nd(L)(NO ) (Me CO)] complex contains the central
3
2
neodymium cation chelated by the bidentate ligand L
and three bidentate nitrate ions, and the ninth coordina-
tion site is occupied by the acetone molecule (Fig. 1).
The Nd–O(P) bond lengths differ insignificantly, being
P(O)Ph2
Me
Me
P(O)Ph2
L
2.323(7) and 2.349(7) Å. The Nd–O(N) bond lengths
vary within 2.489(8)–2.571(7) Å, and the Nd–O(1s)
bond length is 2.476(9) Å. The other bond lengths and
angles are typical of structures of this type. Full X-ray
diffraction experiment data will be published else-
where. The vibrational spectra of these complexes are
identical to the spectra of I, which ultimately confirms
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
9
5

9
6
MATVEEVA et al.
C11
C10
C6
C1
C7
C23
C2
C22
C29
C9
C5
C21
C28
C3
O5
C18
C4
O3
C8
C24
P2
N1
C20
C27
P1
C19
C25
O1
O2
C26
O4
O10
C12
C17
C30
Nd6
C35
C34
C31
C13
N3
O6
N2
C16
C32
C33
C14
C15
O1s
O7
O9
O11
C1s
C1s'
O8
C2S
C3S
C2S'
Fig. 1. Crystal structure of the complex [Nd(L)(NO ) · Me CO].
3
3
2
the proposed structure of the monoligand complex I in do not change with temperature in the range 253–
the solid phase.
343 K. However, the signal positions depend substan-
tially on the solution temperature. As the temperature
increases, both signals shift upfield and simultaneously
approach each other (Fig. 2). The temperature depen-
dence is reversible.
We assumed that equilibrium (1) is established in
acetonitrile solutions of complex I (n = 1), where A is
the neutral complex, B is the cationic complex (ion
pair), and C is the free ion in the solution bulk.
Complexes I and II are almost insoluble in CHCl3,
CH Cl , benzene, and toluene and are sparingly soluble
2
2
in MeCN and MeOH. As expected, monoligand com-
plex I is much less soluble than bisligand complex II.
Upon dissolution in DMSO, the complexes are com-
pletely destroyed. The structures of the complexes were
studied in acetonitrile solutions.
According to IR spectroscopy data, the structure of
complex I is retained in solution. The IR spectrum of a
solution of I does not differ much from the spectrum of
the solid sample. The bands of the bidentately coordi-
nated nitrate groups do not change; the only band for
0
+
–
[
Nd(L) (NO ) ]
[Nd(L) (NO ) ] ⋅ (NO )
2
n 3 3
n
A
3
3
B
+
–
[
Nd(L) (NO ) ] + (NO ) .
(1)
n
3
2
3
C
–
1
P=O groups shifts slightly (1148 cm ). No band for
The presence of different numbers (two or three) of
nitrate ions in the inner coordination sphere of the com-
plex can substantially affect the shielding of the phos-
phorus atoms of the coordinated ligand. In this case, the
free NO groups is present. The OH vibration region
3
–
1
contains two bands, at 3550 and 3630 cm , typical of
free water molecules in MeCN [3].
3
1
31
The P NMR spectrum of the same solution (298 K)
exhibits, in the expected region, two rather than one
broadened (halfwidths 97 and 81 Hz) signals at 137.8
and 131.5 ppm with an integrated intensity ratio of
P NMR signals of phosphorus incorporated in neutral
species A will occur in a higher field than the signals of
species B and C (131.5 and 137.8 ppm, respectively).
The difference between the two types of ion pairs (com-
plexes) existing at low temperatures may become
uncertain or disappear with increasing temperature [7].
Indeed, as the temperature is raised, the signals in the
spectra of complex I approach each other (at 333 K,
0
.27 : 1; no signal for the free ligand is present. A sim-
ilar spectral pattern has been observed previously for
lanthanide nitrate complexes with other phosphoryl
ligands [4–6].
The molecular weight of complex I measured in a ∆δ = 2.7 ppm). (In the spectra of complex II (see
MeCN solution was 874, which corresponds to within below), the signals overlap at 333 K and coalesce at
the experimental error (±5%) to the calculated weight 343 K.)
(
879) for the mononuclear [NdL(NO ) ] complex.
3 3
The position of equilibrium (1) should depend on
Thus, other species that could be responsible for an the concentration of free nitrate ions. Indeed, upon the
3
1
observed P NMR signal may be excluded from con- addition of Bu NNO , the relative concentration of neu-
sideration.
4
3
tral species A (the signal at 131.5 ppm) sharply
increases (Fig. 3).
3
1
A study of the temperature dependence of the P
NMR spectra of solutions of I has shown that the inte-
grated intensity ratio and the signal halfwidths almost plex I in MeCN and low fraction of species B and C,
Unfortunately, due to the low solubility of com-
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2
,4-BIS(DIPHENYLPHOSPHORYLMETHYL)MESITYLENE COMPLEXES
97
c
b
a
120
1
90
180
170
160
150
140
130
110
ppm
Fig. 2. Temperature evolution of the 31P{ H} NMR spectra of complex I in CD CN: (a) 253, (b) 273, and (c) 293 K.
1
3
the IR spectra of solutions do not exhibit the expected the ligand to the solution gives rise to a signal at 29 ppm
–
1
band for the free nitrate ions at ~1380 cm . The elec- with the expected intensity, while the integral intensity
trical conductivity data confirm the low content of ratio of the signals at 137 and 128 ppm almost does not
free ions in the solution of I. The electrical conduc- change. As a first approximation, this allows one to
–
1
–1
exclude additional equilibria involving L from consid-
eration.
tivity of a 0.001 M solution of I (11.69 Ω cm mol)
is much lower than that for the 1 : 1 electrolyte
–1
–1
–
1
Bu NNO (155.3 Ω cm mol).
4
3
In addition to the bands at 1470 and 1310 cm for
the NO groups coordinated in the bidentate mode, the
3
Bisligand complex II in a MeCN solution demon-
strates a similar behavior differing only by the position
of equilibrium (1), which is shifted to the right with
respect to that for complex I. According to the spatial
requirements of the metal coordination polyhedron, the
relative content of molecular formA in solutions of bis-
ligand complex II should be smaller than that in solu-
tions of monoligand complex I. The P NMR spectrum
298 K) exhibits two broadened signals at 137.5 and
28.3 ppm with an intensity ratio of 1 : 0.5, which can
be attributed, as in the case of monoligand complex I,
to the cationic (B, C) and neutral (A) species, respec-
tively. The molecular weight of complex II determined
in a solution in MeCN is 1372. This corresponds, to II (96.92 Ω cm mol) is much higher than that for
within the experimental error, to the value calculated complex I. Thus, complex II, unlike I, is essentially
for [Nd(L) (NO ) ] (1423). The temperature depen- dissociated; this allows us to observe a band for the free
–1
IR spectra of solutions of II exhibit a band at 1380 cm
for the free nitrate ion. The IR spectrum does not con-
tain any band differences that could be reliably inter-
preted as vibrations of the outer-sphere nitrate ion in
species B.As a first approximation, one can assume that
its symmetry does not differ from the symmetry of the
free ion. For example, for perchlorate ion, it is known
3
1
[
7] that the symmetry of the counterion in outer-sphere
(
1
complexes (solvent-separated ion pairs) is not distorted
and does not differ from the free ion symmetry in solu-
tion.
The electrical conductivity of a 0.001 M solution of
–1
–1
2
3 3
1
3
nitrate ion in the IR spectra.
dence of the P NMR spectra and the effect of
Bu NNO additives on the signal intensity ratio are
similar to those found for complex I. The addition of 1 and 1 : 2 molecular complexes in which both the
4
3
Thus, the dioxide L and neodymium nitrate form 1 :
DOKLADY CHEMISTRY Vol. 413 Part 2 2007

9
8
MATVEEVA et al.
c
b
a
1
90 180 170 160 150 140 130 120 110 100 90 80 70
ppm
Fig. 3. 31P{ H} NMR spectra of complex I in CD CN after addition of (b) 2.6 and (c) 5.3 equiv of Bu NNO ; (a) the initial
1
3
4
3
solution.
ligand L and the nitrate groups are coordinated in the with hexane (20 mL). The precipitated solid was sepa-
bidentate mode. In acetonitrile solutions, the molecular rated, washed with hexane (2 × 10 mL), recrystallized
complexes [Nd(L) (NO ) ] (n = 1, 2) are equilibrated twice from an ethanol–acetonitrile mixture (1 : 4), and
n
3 3
+
–
dried in vacuum at 100°C over P O . Yield 2.3 g
with ion pairs [Nd(L) (NO ) ] · (NO ) and with free
2
5
n
+
3 2
3
–
(80.0%), mp 211–212°C (ethanol–acetonitrile).
ions [Nd(L) (NO ) ] and (NO ) . The equilibria
n
3 2
3
between the molecular complexes and cationic species
as ion pairs and in the free state) can be observed in
solutions of the neodymium nitrate complexes with
phosphoryl-containing ligands by P NMR spectros-
copy.
For C H O P anal. calcd. (%): C, 76.35; H, 6.22;
P, 11.61.
3
5
34
2 2
(
3
1
Found (%): C, 76.31; H, 6.17; P, 11.03.
3
1
1
1
P{ H} NMR (CDCl , δ, ppm): 28.90. H NMR
The 31P NMR spectra of solutions of lanthanide
3
(
(
CDCl , δ, ppm, J, Hz): 1.83 (s, 3 H, C -1-Me); 1.89
3 Ar
nitrate complexes with phosphoryl-containing ligands,
described previously as unusual [4–6], are naturally
interpreted within the framework of the proposed equi-
librium of molecular complexes, ion pairs, and free
ions and are consistent with the experimental data
reported in the above-mentioned studies.
s, 6 H, C -3-Me and C -5-Me); 3.70 (d, 4 H, C(2)-
Ar
Ar
CH –P and C(6)-CH –P, 16.0); 6.68 (s, 1 H, C(4)-H);
2
2
7
.39–7.65 (m, 20 H, 2 P–Ph2).
Synthesis of the complexes. The complexes I and
II were prepared by the reaction of equimolar amounts
of ligand and salt solutions.
EXPERIMENTAL
The complex [Nd(L)(NO ) ] · H O (I). A solution
3
3
2
Materials and chemicals. Pure grade solvents were of Nd(NO
) · 6H O (0.0569 g, 0.1310 mmol) in MeCN
purified by known procedures. The salt Nd(NO ) · (2 mL) was added to a solution of ligand L (0.0999 g,
3 3 2
3
3
0
.1310 mmol) in CHCl (2 mL). The precipitate was
6
H O (Fisher Scientific Company) was used as
received. The solvents for spectroscopic studies were
prepared by the volume-weight method.
3
2
separated, washed with anhydrous ether, and dried in
vacuum over P O at room temperature. This gave
2
5
0
.106 g (66.7%) of complex I as a light pink powder
2
,4-Bis(diphenylphosphorylmethyl)mesitylene
with Tdecomp > 175°C.
(
(
L). A mixture of 2,4-bis(bromomethyl)mesitylene
1.6 g, 5.2 mmol) [8] and Ph POMe (2.5 g, 11.6 mmol)
2
For C H N NdO P anal. calcd. (%): C, 46.87; H,
3
5
36
3
12 2
in xylene (12 mL) was heated at 140°C in a nitrogen
flow for 40 min. Half of the solvent was distilled off and
the remaining warm solution was poured into a flask
4
.05; N, 4.69.
Found (%): C, 46.54; H, 3.89; N, 4.92.
DOKLADY CHEMISTRY Vol. 413 Part 2 2007

2
,4-BIS(DIPHENYLPHOSPHORYLMETHYL)MESITYLENE COMPLEXES
99
The complex [Nd(L) (NO ) ] · 4H O (II) was pre- President of the Russian Federation for State Support of
2
3 3
2
pared similarly to complex I. Yield 70%, a light pink Leading Scientific Schools (grant nos. NSh–1100–
powder (lighter than complex I) with Tdecomp > 200°C.
2003–3 and NSh–1060–2003–3).
For C H N NdO P anal. calcd. (%): N, 2.80;
7
0
76
3
17 4
P, 8.26.
REFERENCES
Found (%): N, 2.95; P, 7.70.
IR spectra (400–3700 cm ) were recorded with a
Nicolet Magna IR-750 Fourier Transform IR spectro-
photometer. The samples were prepared as KBr pellets,
mineral oil and hexachlorobutadiene mulls, and 0.03–
1
2
. Kabachnik, M.I., Heteroatom. Chem., 1991, vol. 2, no. 1,
–
1
pp. 1–10.
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0
.2 M solutions in MeCN (NaCl or CaF cells; l = 0.07–
.12 mm).
2
Raman spectra were recorded for solid samples on
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5
14.5 nm.
1
31
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4
5
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4
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3
1
etc.) were used as the internal standard for the H NMR
spectra; 85% H PO served as the external standard for
3
4
6
7
. Deakin, L., Levason, W., Popham, M.C., Reid, G., and
Webster, M., J. Chem. Soc., Dalton Trans., 2000, no. 14,
pp. 2439–2447.
3
1
the P NMR spectra.
The molecular weights of complexes I and II in ace-
tonitrile solutions were determined by sedimentation
analysis according to known procedures [9].
The electrical conductivity of 0.001 M solutions of
complexes I and II and Bu NNO in MeCN were mea-
. Gordon, J., The Organic Chemistry of Electrolyte Solu-
tions, New York: Wiley, 1975. Translated under the title
Organicheskaya khimiya rastvorov elektrolitov, Mos-
cow: Mir, 1979.
4
3
sured at 298 K on a PM 6306 instrument (Fluka).
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Chem., 1993, vol. 58, no. 5, pp. 1262–1263.
9
. Gavrilov, K.N., Mikhel’, I.S., Lysenko, K.A.,
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ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research and by the Council for Grants of the
DOKLADY CHEMISTRY Vol. 413 Part 2 2007