N-tris[(2-aminoethyl)-2-(diphenylphosphoryl) acetamide)] - Novel CMPO tripodand: Synthesis, extraction studies and luminescent properties of lanthanide complexes

Article abstract of DOI:10.2478/s11532-011-0124-5

A ligand system containing three carbamoylmethylphosphine oxide (CMPO) moieties attached to a tripodal platform with a central nitrogen atom has been synthesized for metal complexation and extraction from neutral and nitric acid solutions. Liquid-liquid e

Full text of DOI:10.2478/s11532-011-0124-5

Cent. Eur. J. Chem. • 10(1) • 2012 • 146-156
DOI: 10.2478/s11532-011-0124-5
Central European Journal of Chemistry
N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl)
acetamide)] - novel CMPO tripodand: synthesis,
extraction studies and luminescent properties
of lanthanide complexes
Research Article
Elena V. Sharova1, Oleg I. Artyushin1, Alexander N. Turanov2,
Vasilii K. Karandashev3, Svetlana B. Meshkova4,
Zoya M.Topilova4, Irina L. Odinets1*
1A. N. Nesmeyanov Institute of Organoelement Compounds, Russian
Academy of Sciences, 119991 Moscow, Russia
2Institute of Solid State Physics, Russian Academy of Sciences,
142432 Chernogolovka, Russia
3Institute of Microelectronics Technology and High Purity Materials,
Russian Academy of Sciences, 142432 Chernogolovka, Russia
4A.V. Bogatsky Physico-chemical Institute,
National Academy of Sciences of Ukraine, 65080 Odessa, Ukraine
Received 21 July 2011; Accepted 25 September 2011
Abstract:
A ligand system containing three carbamoylmethylphosphine oxide (CMPO) moieties attached to a tripodal platform with a central
nitrogen atom has been synthesized for metal complexation and extraction from neutral and nitric acid solutions. Liquid–liquid
extractions performed for Ln(III), both from neutral and acidic media, show excellent extraction properties which exceeded those
for the known mono- and di-CMPO derivatives as well as the related tripodands. A considerable enhancement of the DLn
values was observed in the presence of IL ([bmim][Tf2N]) in the organic phase towards lanthanide ions from 3M HNO3 solutions.
Theprotonationofthecentralaminenitrogenatomoftheligand1intheacidicmediaprovidesalsotheeffectiveextractionoftheperrhenate
anionic complexes. The europium complexes formed by mono- and tris-CMPO ligands in the solid state, as well as Eu(III) and Tb(III)
complexes generated in solutions, possess intensive luminescence at 300K
Keywords: Carbamoylmethylphosphine oxides • Lanthanides(III) • Ionic liquids • Extraction • Luminescence
© Versita Sp. z o.o.
1. Introduction
It is well known that organophosphorus compounds are
inclined to form strong complexes with hard transition
Nowadays, a lot of research groups focus their efforts on and rare-earth metal ions [4,5]. Among those, bidentate
the targeted design of artificial receptors for the selective phosphorus analogs of acetylacetonate ligands bearing
recognition of cations and anions [1]. The tripodal the donor oxygen atoms in 1,3-positions such as those
receptors belong to a special class of acyclic ionophores, of two phosphoryl groups or of the combination of P=O
which consist of multi-armed ligands with each arm and C=O (carbonyl, carbalkoxy or carbamoyl) functions
bearing functional group(s) that can coordinate with the are good chelating ligands for trivalent lanthanide and
target ion. In general the number of tripodal ligands for actinide ions and, therefore, display useful extraction
actinide and/or lanthanide complexation is still rather and sorptions properties towards these elements [6-10].
limited [2,3].
Among those, carbamoylmethylphosphine oxides
* E-mail: odinets@ineos.ac.ru
146

E. V. Sharova et al.
(CMPO), for example (N,N-diisobutylcarbamoylmethyl) or externally to H3PO4 (31P). The 13C NMR spectra were
octylphenylphosphine
oxide
[11,12]
or
(N,N- registered using the JMODECHO mode; the signals for
dibutylcarbamoylmethyl)diphenylphosphine
oxide the C atoms bearing odd and even numbers of protons
[13], are known to be preferable among the typical have opposite polarities. IR spectra were recorded
extractants for processing of accumulated liquid acidic on a Magna-IR 750 FTIR spectrometer (Nicolet Co.,
radioactive wastes in terms of cost and effectivity. The resolution 2 cm-1, scan number 128, KBr pellets). Melting
effectivity and selectivity of such ligands usually increase points were determined with an Electrothermal IA9100
with an increase in the amount of CMPO residues in a DigitalMelting Point Apparatus and were uncorrected.
molecule [14]. Attachment of CMPO groups to molecular
The known ligands 2-5 [14,31] were obtained via
platforms such as calixarenes [15-17] and cavitands the procedures described in the literature, and their
[18-21] led to further increase of extraction efficiencies physicochemical constants matched the literature data.
and selectivities.
N-tris[(2-aminoethyl)-2-(diphenylphosphoryl)
However, as only three CMPO moieties are acetamide)] 1
necessary for the coordination of a f-element ion, the
Phosphorus trichloride (1.1 g, 0.0077 mol) was
corresponding tripodal CMPO ligands are of undoubted added dropwise with stirring and cooling to 0oC (an
interest. Nevertheless, currently reported are only a few ice-bath) to a slurry of phosphorylacetic acid (5.0 g,
examples of a tripodal platform with substituted trityl 0.019 mmol) in anhydrous CHCl3 (15 mL). Then the bath
[22-24] skeleton and different rearrangement of CMPO was removed and the mixture was stirred at 20oC for
moieties, the related compounds with thiophosphoryl 5 h and again cooled to 0oC. A solution of triethylamine
function [25], and those on trimethylolpropane-based (4.7 g, 0.046 mmol) and tris-(2-aminoethyl)amine
tripodal framework [26]. These tripodal receptors, (0.7 g, 0.0051 mol) in anhydrous CHCl3 (5 mL) was
excluding the thiophosphoryl derivatives, show slowly added dropwise. The reaction mixture was
reasonable extraction properties towards lanthanides stirred at 20oC for 2 h and allowed to stand overnight.
and actinides in 1,1,2,2-tetrachloroethane, and 1,1,1-tris Then water (20 mL) and DCM (15 mL) were added,
[(diphenylcarbamoylmethylphosphine oxide N-propoxy) the organic layer was separated, washed with water
methyl]propane demonstrated high selectivity towards (50 mL), dried with Na2SO4, and filtered. The solvent
Eu3+ and forms a very stable complex (log βML = 28.3). was removed in vacuo, and the residue was purified by
However, in many cases extractions using known recrystallization from ethanol (twice) and dried in vacuo
tripodal CMPO ligands suffer from third phase formation over P2O5 to constant weight to give 1.4 g of a sodium
and the systems developed were effective at low HNO3 complex of the compound. The slurry of this complex
concentration only.
was stirred in water for 20 min, the precipitate was
Therefore, incontinuationofourgroupresearchinthe filtered off and washed with ether to give after being
field of neutral [27-29] and ionic [30] CMPO derivatives, dried over P2O5 the desired compound as a hydrate.
in this paper we report on the synthesis and extraction Yield: 32%. Mp: 192°C (dec). IR (KBr, cm-1): 3277 (νNH),
study of the novel tripodal CMPO ligand which shows 3059, 2955, 2918, 2818, 1665 (νC=O), 1590, 1547 (νNH),
excellent extraction properties exceeding those for the 1438 (νCH2), 1312, 1299, 1176 (νP=O), 1121, 1101, 1071,
known mono- and di-CMPO derivatives as well as the 1028, 998, 847, 746, 729, 694, 517. 1H NMR (300 MHz,
related tripodands both in neutral and acidic medium. CDCl3, ppm, J/Hz): 2.43-2.47 (m, 6H, NCH2); 3.12-3.17
Furthermore, taking into account the growing interest (m, 6H, NCH2CH2); 3.63 (d, 6H, PCH2, 2JP-H=14.3); 7.39-
in luminescent systems based on f-elements and ability 7.43 (m, 12H, m-C6H5P); 7.52-7.54 (m, 6H, p-C6H5P);
of CMPO derivatives to form strong complexes with 7.71-7.78 (m, 12H, o-C6H5P); 8.62 (br. s, 3H, NH).
lanthanides, we describe for the first time luminescent 31P NMR (121.5 MHz, CDCl3): 30.25 ppm. 13C NMR
properties of Eu and Tb complexes formed by CMPO (75.47 MHz, CDCl3, ppm, J/Hz): 37.58 (NCH2), 38.81
ligands, including the novel tripodand.
(d, PCH2, 1JPC=62.6), 52.89 (NCH2CH2), 128.45 (d, m-C
3
2
in C6H5, JPC=12.1), 130.69 (d, o-C in C6H5, JPC=9.9),
4
131.79 (d, p-C in C6H5, JPC=1.6), 131.99 (d, ipso-C in
1
2
2. Experimental procedure
C6H5, JPC=102.6), 164.43 (d, C(O), J PC=5.5). Anal.
Calcd for C48H51N4O6P3•H2O: C, 64.71; H, 6.00; N, 6.29.
Found: C, 64.73; H, 5.77; N, 6.09.
2.1. General remarks
The NMR spectra were recorded on a Bruker AMX-300
instrument in CDCl3 and CD3OH solutions. The chemical
[Eu{N(CH2CH2NHC(O)CH2P(O)Ph2)3}Cl3]
An ethanolic solution (3 mL) of the EuCl3 (46 mg,
shifts (δ) were internally referenced by the residual 0.126 mmol) was added dropwise to a solution of the
solvent signals relative to tetramethylsilane (1H and 13C) ligand 1 (113.0 mg, 0.129 mmol) in 4 mL of C2H5OH
147

N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl)acetamide)] -
novel CMPO tripodand: synthesis, extraction studies
and luminescent properties of lanthanide complexes
and in 2 mL CH3CN. The resulting mixture was left measurements was generally within 10%. The nitric
under ambient conditions for 2 h and evaporated to a acid concentration in the equilibrium aqueous solutions
volume of ~1 mL. Addition of ether (5 mL) to the reaction was determined by potentiometric titration with KOH
solution afforded precipitation of the corresponding solution.
complex which was filtered off, washed with 10 mL
of Et2O and dried in vacuum. Yield: 77%. Mp: 194°C 2.3. Luminescence
(dec.). IR (KBr, cm-1): 3348, 3219, 3056, 2949, 2897, The luminescence spectra of the complexes in a solid
1625 (νC=O), 1590, 1566, 1438 (νCH2), 1399, 1330, state and in solutions were registered on a luminescent
1160 (νP=O), 1139, 1124, 1096, 1072, 1027, 997, 847, spectrometer SDL-1 (St.-Peterburg). The Hg lamp
734, 694, 527, 508. 31P NMR (121.5 MHz, CD3OH): equipped with UFS-2 colour filter for detachment of
0.70 ppm. Anal. Calcd for C48H51Cl3EuN4O6P3: C, 50.97; most intensive mercury lines 313 and 365 nm was used
H, 4.54; N, 4.95. Found: C, 50.84; H, 4.57; N, 4.81.
for excitation. The luminescence was measured on
solid samples put into 10×5×45 mm cuvette with 1 mm
deepening and 7 mm diameter. For solutions, quartz
10×10×45 mm cuvette was used.
2.2. Extraction properties
Chemical-
and
analytical-grade
nitrobenzene,
1,2-dichloroethane,
1,1,2,2-tetrachloroethane,
and chloroform were used as diluents. Extractant
solutions in the organic diluents were prepared from
precisely weighed amounts of the reagents. The initial
3. Results and discussion
concentration of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, 3.1. Synthesis of the ligands
Er, Tm, Yb, Lu, Y, U, Th, Re, Fe, Al, Cu, Pb, Zn, Cd, Ni, The desired tripodand 1 was synthesized using the
Co, Mn, Ca, Sr, and Ba was 1×10-5 M for each element. general synthetic procedure detailed by us earlier,
All lanthanides (III) (except Pm) were presented in the namely via the reaction of diphenylphosphorylacetic
initial aqueous phase when simultaneous extraction of acid chloride generated in situ in the presence of
Ln(III) was studied. The experiments were carried out in phosphorus trichloride with amines [21]. For construction
ampules with ground stoppers at 20-25oC. The volumes of tripodal framework, we used tris(2-aminoethyl)amine
of both organics and aqueous phases were equal to as N-nucleophile. Note that after the ordinary work-up
2 mL. The solution was stirred on a rotary mixer for procedure involving drying over sodium sulfate, the
an hour at 60 rpm to achieve equilibrium. Preliminary final ligand was isolated as the corresponding sodium
experiments showed that this time exceed the time complex which was destroyed by water treatment
required for the system to reach the equilibrium. After (see experimental). Therefore, to avoid such complex
the extraction, 0.5 mL of the aqueous solution was taken formation, application of typical driers should be
for further analysis. A portion of the organic phase was excluded from this procedure.
transferred to another glass tube, and a specific volume
The pure ligand 1 demonstrates a singlet at
of the 1-hydroxyethane-1,1-diphosphonic acid solution ca. 30 ppm in the 31Р NMR spectrum, i.e., the
was added. The mixture was shaken for 20 min and region characteristic for the given phosphorus atom
Ln(III) in the organic phase were back extracted into the environment.The 1H NMR spectrum corresponds to
aqueous phase.
the depicted structure and is comprised of a doublet of
The metal concentrations in the initial and equilibrium protons of the PCH2 group at 3.63 ppm with a coupling
aqueous solutions after extraction and back extraction constant of 14.3 Hz along with the other characteristic
were determinated by inductively coupled plasma signals of the hydrogen atoms located in the typical
mass-spectrometry (ICP-MS) on a PlasmaQuad mass regions. In the IR spectrum characteristic absorption
spectrometer with quadrupole mass analyzer (VG bands at 1665 cm-1 (С=О) and 1176 cm-1 (Р=О) along
Elemental, GB) [32]. The distribution ratios of metal ions with absorption of NH group appearing as a broad band
(D) were calculated as the ratio of concentrations in at 3277 cm-1 (valent oscillations) and a band at 1547 cm-1
the equilibrium organic and aqueous phases. Duplicate (component frequencies of NH deformation oscillations
experiments showed that the reproducibility of the DLn and C-N oscillations) were observed.
For comparison, experiments in the extraction
O
P
O
O
1. PCl3
O
CHCl3, 0 0C
study and luminescence properties of the complexes
we performed also the synthesis of related derivatives
2-5 differing in the amount of CMPO groups in the
molecule and substituents at the nitrogen atom. These
comparative ligands were obtained via the direct
Ph
Ph
N
Ph2P
COH
3
2. N(CH2CH2NH2)3
N
H
1
Scheme 1. Synthesis of the tris-CMPO ligand 1.
148

E. V. Sharova et al.
of the ligands was [1]:[2]:[3] was 1:1.5:3 in order to
achieve the similar concentration of Ph2P(O)CH2C(O)
N< moieties in the organic phase. Fig. 1 indicates that
an increase in the amount of bidentate complexing
Ph2P(O)CH2C(O)N< groups in a molecule results in
the increase in the extraction efficiency towards Ln(III).
For compound 2, the extraction of lanthanides(III)
increased from La(III) to Sm(III) and later on
decreased from Sm(III) to Lu(III). Similar pattern of
lanthanide extraction was observed for compound
2 [14] as well as other neutral bidentate ligands such
as tetra(p-tolyl)methylenediphosphine dioxide [34]
carbamoylmethylphosphine oxides (CMPO) [35],
O
P
O
O
P
O
Ph
Ph
Ph
Ph
C9H19
CH2
N
H
2
N
H
2
3
O
P
O
P
O
O
Ph
Ph
Ph
Ph
C4H9
C4H9
C4H9
H
N
N
4
5
Scheme 2. The comparative mono- and bis-CMPO ligands used
in the study.
amination of ethyl diphenylphosphorylacetate via the
other general procedure developed by us previously
[14-31].
N,N’-dimethyl-N,N’-diphenylmalonamide
[36]
as
well as calix[4]- and calix[5]arenes modified by a few
Ph2P(O)CH2C(O)N functions at their wide rim [17] in
nitric acid systems. These trends in logDLn vs. atomic
number (Z) were explained [35] by an increase in the
hydration energy of the Ln3+ ion as Z increased, thereby
decrease in the ability of extractants to dehydrate
Ln3+ over the extraction. For compound 1, DLn tends
to increase as Z increases (Fig. 1) probably due to
participation of the central nitrogen atom in complexation
with heavy Ln(III) over the extraction from neutral
media. In this context, it should be mentioned that
exchange of the ether oxygen in the molecule of podand
3.2. Extraction experiments
3.2.1. Extraction of lanthanides(III) from neutral media
As known lanthanide(III) ions are extracted with neutral
organophosphorus compounds as solvates LnLsA3
(where L is neutral extractant, A - a counterion, and s -
Ln:L stoichiometric ratio). The nature of the counterion
affected significantly hydrophobicity of solvates formed
and their transfer from aqueous to organic phase. Thus,
efficiency of extraction of Eu(III) by 0.002 М solution
of compound 1 in 1,2-dichloroethane from 1 M NH4Cl,
1 M NH4NO3 and 1 M NH4ClO4 solutions increases in a
series NH4Cl(logDEu < - 2.5) < NH4NO3(logDEu = - 0.9)
< NH4ClO4(logDEu =3.15) with decreasing hydration
energies of the relevant anions, that is, with increasing
hydrophobicity of extracted Ln(III) complexes as far
as hydrophobic properties of a counterion increased.
The nature of an organic diluent also substantially affects
the lanthanides(III) extraction efficiency. For example, in
the extraction of Eu(III) from 4 М NH4NO3 solutions the
Ph2P(O)(CH2)2O(CH2)2O(CH2)2O(CH2)2P(O)Ph2
for
-NBu group results in sufficient increase of Ln(III)
extraction efficiency from neutral NH4NO3 solutions [37].
At the same time, when this nitrogen atom is protonated
in 4 M HNO3 solution the inversion of the trend lgDLn
vs. Z for compound 1 (Fig. 2) was observed and the
difference in the DLn values DLn(NH4NO3)/DLn(HNO3)
increased with an increase of Z.
efficiency increased in the order: chloroform (logDEu
=
-0.55) < 1,1,2,2-tetrachloroethane (logDEu = -0.43) < 1,2-
dichloroethane (logDEu = -0.22) < nitrobenzene (logDEu
= 0.2) in parallel with an increase of dielectric constant
of a diluent and its solvating power. The same tendency
noted previously by Rozen et al. [33] in the study of the
diluent effect on the extraction of Eu(III) and Am(III)
with neutral bidentate organophosphorus compounds,
namely tetraphenylmethylenediphosphine dioxide and
3.2.2. Extraction of lanthanides(III) from nitric acid
solutions
Fig. 3 shows the effect of HNO3 concentration in the
aqueous phase on the simultaneous extraction of
lanthanides(III) by solution of compound 1 in 1,2-
dichloroethane. As one may see, the log DLn vs. log
[HNO3] curve exhibits maxima at [HNO3] = 3 M for La
- Tb and at [HNO3] = 4 M for Tm and Ho. These maxima
are commonly observed in metal extraction by neutral
organophosphorus compounds and are explained by
combined effect of HNO3 salting out and competition
for the extractant molecule by co-extraction of HNO3.
The maximum of log DLn shift towards higher [HNO3]
valuesonpassingfromLa(III)toHo(III),whichisevidently
associated with an increase in the hydration energy of
the Ln3+ ion, as Z increases. For the heavier Ln(III), DLn
increases with the increase of HNO3 concentration up to
7 M HNO3 (Fig. 3).
diphenyl(dibutylcarbamoylmethyl)phosphine
oxide,
was explained by the specific solvation of the complex
extracted by an organic diluent.
The effect of the number of CMPO groups
in the molecule of the ligand on the efficiency of
lanthanides(III) extraction was examined using the
related derivatives 2 and 3. In other words, the
simultaneous extraction of Ln(III) ions from 4 M NH4NO3
by solutions of compounds 1-3 in 1,2-dichloroethane
was carried out. The ratio of the initial concentrations
149

N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl)acetamide)] -
novel CMPO tripodand: synthesis, extraction studies
and luminescent properties of lanthanide complexes
actinides, the extractant dependences for U(VI) and
Th(IV) were studied at the same HNO3 concentration
in the aqueous phase. Fig. 4 demonstrates that both
Th(IV) and U(VI) are extracted with compound 1 more
effectively than Ln(III).
The second power dependence of DLn on [L] indicates
that Ln(III) are extracted from nitric acid solutions by
compound 1 as disolvates. In contrast, mono-CMPO
derivative 3 extracts Ln(III) from 3M HNO3 solutions as
tri- and tetra-solvates (Fig. 4). Therefore, the tripodand
CMPO-derivative extracts Ln(III) ions more effectively
compared with compound 3. The difference in extraction
ability for compounds 1 and 2 is less pronounced, e.g.
in the case of the extraction with 0.005 M solutions in
dichloroethane from 3 M HNO3 the DEu values were 1.75
and 0.77 [14], respectively. Furthermore, comparison
of the Eu(III) extraction from 1 M HNO3 with 0.014 M
solutions in 1,1,2,2-tetrachloroethane of compound 1
and its structural analog – tripodand 1,1,1-tris[(diphe-
nylcarbamoylmethylphosphine oxide N-propoxy)methyl]
propane [26], demonstrates that the former possess
better extraction ability (DEu = 1.55 and 0.26 [26],
respectively).
Figure 1.
The extraction of lanthanides(III) from 4 M NH4NO3 media
with solutions of compounds 1-3 in 1,2-dichloroethane.
Initial extractant concentrations are 0.00333
M
(compound 1), 0.005 M (compound 2) and 0.01 M
(compound 3).
3.2.3.
Extraction of metal ions from nitric acid solutions
in the presence of picric acid
The Ln(III) extraction with CMPO is known to increase
significantly in the presence of picric acid. This fact is
connected with the participation of hydrophobic Pic-
anionsintheformationofextractablecomplexes[38].The
same synergistic effect is observed over the extraction
of Ln(III) from slightly acidic solution with the ligand 1 in
the presence of HPic in the organic phase. In this case
the Ln(III) extraction decreased as the concentration
of HNO3 in the aqueous phase increased (Fig. 5a) and
that may be connected with the inhibition of the HPic
dissociation and decrease of Pic- anion concentration
in the aqueous phase. Figs. 5b and 5c indicate that the
stoichiometric ratio Ln:L:Pic in extracted complexes is
1:2:3. The simultaneous extraction of lanthanides(III)
by solutions of compound 1 in 1,2-dichloroethane in
the presence of picric acid has revealed that tris-CMPO
1 is significantly more effective than its mono-CMPO
analogue 3 in such systems (Fig. 6).
Figure 2. The
extraction of lanthanides(III) from
and 4 M HNO3 solutions with 0.01 M solution of compound
4 M NH4NO3
1 in 1,2-dichloroethane.
The simultaneous extraction of some tri- and
dicharged cations by the solution of compound 1 and
picric acid in 1,2-dichloroethane was also studied. Thus,
the ligand 1 was found to be an effective extractant for
alkaline earth metal ions from the diluted HNO3 solutions
in the presence of HPic in the organic phase (Table 1).
To compare the extraction efficacy of compounds 1, 2
and 3 towards these ions, Table 2 shows distribution
coefficients for the extraction of Ca2+, Sr2+, and Ba2+ from
Figure 3.
The effect of HNO3 concentration in the aqueous phase
on the extraction of lanthanides(III) with 0.01 M solutions
of compound 1 in 1,2-dichloroethane.
The variations in DLn as a function of concentration
of the tripodand 1 in 1,2-dichloroethane for 3M HNO3
systems are shown in Fig. 4. To compare the extraction
efficiency of compound 1 towards Ln(III) with that for
150

E. V. Sharova et al.
a)
b)
c)
Figure 4. The effect of the concentration of extractants 1 and 3
in 1,2-dichloroethane on the extraction of Ln(III), Th(IV)
and U(VI) from 3 M HNO3 solutions.
HNO3 solutions. Obviously, the extraction efficiency
increases in the order 3 < 2 < 1 along with the increase
of the number of CMPO moieties in the ligand molecule.
Note that for the ligands 2 and 3 the efficiency of alkaline
earth metal ions increases in the order Ba2+ < Sr2+
<
Ca2+ in parallel with the increase in the positive charge
density of M2+ ions. This tendency suggests that the
interaction between these ligands and M(II) has mainly
the electrostatic character [39].
In contrast, the efficiency of alkaline earth metal ion
extraction increases in the order Ca2+ < Sr2+ < Ba2+ in
the case of tris-CMPO 1 (Table 2) and the same order
was observed for the extraction of these ions with
macrocyclic ligands. The difference in the stoichiometry
of the extracted complexes of the alkaline earth metal
ions has been also revealed: in the system based on
compound 1 complexes of the composition M:Pic:L =
1:2:1 transfer to the organic phase, while in the system
formed with the analogs 2,3 this ratio was 1:2:2.
3.2.4. Extraction of lanthanides(III) from nitric acid
solutions into ionic liquid
a) The effect of HNO concentration in the aqueous
phase on the extractio3n of Tb(III) by 0.01 M solutions
Figure 5.
The application of ionic liquids (ILs) as new separation
media has been actively investigated recently
[40-43]. Visser and Rogers [42] showed that the
extraction of Pu(IV), Th(IV), and U(VI) into 1-butyl-
3-methylimidazolium hexafluorophosphate ([bmim]
[PF6]) by a mixture of CMPO and tri-n-butylphosphate
is at least an order of magnitude higher than that
observed for the same extractant concentration in
dodecane. Furthermore, CMPO dissolved in [bmim]
[PF6], greatly enhances the extractability and the
selectivity towards lanthanide cations compared with
the solutions in conventional solvents [43]. We have
compared the extraction efficiency of tris-CMPO 1 in
1,2-dichloroethane and 1-butyl-3-methylimidazolium
of
1 in 1,2-dichloroethane and in the presence
0.05 M Hpic; b) The effect of extractant 1 concentrations
in 1,2-dichloroethane on the extraction of Tb(III)
from 0.1
c) The effect of HPic concentrations in 1,2-dichloroethane
on the extraction of Tb(III) from 0.1 M HNO3 solutions
([1]= 0.005 M).
M HNO3 solutions ([HPic] = 0.05 M);
solutions. A considerable enhancement of the DLn values
was observed in the presence of IL in the organic phase
(Fig. 7). An increase in the efficiency of Ln(III) extraction
with the ligand 1 into IL is apparently connected with
incorporation of hydrophobic IL anions into extracted
solvates, which makes them more hydrophobic. Similar
effect is responsible for the considerable enhancement
in Ln(III) and Am(III) extraction with CMPO in the
presence of hydrophobic picrate [38] or chlorinated
cobalt dicarbollide [44] anions.
bis[(trifluoromethyl)sulfonyl]imide
([bmim][Tf2N])
solvents towards lanthanide ions from 3M HNO3
151

N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl)acetamide)] -
novel CMPO tripodand: synthesis, extraction studies
and luminescent properties of lanthanide complexes
Table 1.Extraction
of some metal ions from 0.001
solution by tris-CMPO 1 in the presence of picric acid
M HNO3
in 1,2-dichloroethanea.
Cation
logD
Cation
logD
Fe3+
Al3+
Mn2+
Co2+
Ni2+
1.65
< -1.50
0.56
Zn2+
Cd2+
Pb2+
Ca2+
Sr2+
0.11
0.32
2.03
0.62
1.09
2.15
0.37
0.23
Cu2+
0.16
Ba2+
aConcentration of 1 and HPic 0.025 M.
2+, Sr2+ and Ba2+ from 0.001 M HNO3
solutions by the ligand 1-3 in 1,2-dichloroethane
Table 2. Extraction of Ca
Figure 6.The
extraction of lanthanides(III) from 0.1
solutions with 0.01 M solutions of compounds 1 and 3
M HNO3
in the presence of 0.05 M HPic a.
in 1,2-dichloroethane in the presence 0.05 M HPic.
Cation
log D
1
2
3
Ca2+
Sr2+
Ba2+
0.90
1.35
2.35
0.85
0.62
0.52
-0.40
-0.85
-0.97
aConcentrations were 0.005 M, 0.005 M, and 0.01 M, respectively, for
the ligands 1, 2, and 3
3.2.5. Extraction of ReO4- from acidic solutions
A sufficiently easy protonation of the central amine
nitrogen atom of the ligand 1 molecule in the acidic
media provides also the possibility of extraction of the
anionic complexes, e.g. ReO4- , to the organic phase in
the form of ionic pairs. Fig. 8 shows the effect of HNO3
concentration in the aqueous phase on the extraction of
ReO4- by solutions of compound 1 in 1,2-dichloroethane.
The curve, log DRe vs. log [HNO3], exhibits maximum
at [HNO3] = 0.003 M. This maximum is explained by
combined effect of [H+] on the formation of LH+ cation
and competition for the extractant molecule by the co-
extraction of HNO3. The variations in DLn as a function
of the extractant 1 concentration in 1,2-dichloroethane
solution for 0.1 M HNO3, 0.1 M HCl, 0.1 M HClO4 and
0.1 M H2SO4 systems are shown in Fig. 9. The first
power dependence of DRe on [L] points out that ReO4-
is extracted from acidic solutions by compound 1 as
HLReO4 complexes. As one may see Re(VII) extraction
by solution of compound 1 in 1,2-dichloroethane
increases in the order H2SO4 < HCl < HNO3 < HClO4 in
parallel with increasing hydration energies of the relevant
anions [40], that is, with the increase of hydrophobicity
of co-extracted HLA complexes. Furthermore,
the extraction ability of the tris-CMPO ligand 1 towards
Re(VII) is significantly higher compared withthe related
bis-CMPO 2 and especially mono-CMPO 3 ligands.
Therefore, the novel tripodal CMPO ligand 1 with tris-
N-[(2-aminoethyl)] scaffold possess higher extraction
efficiency towards Ln(III) both from neutral and acidic
media than the corresponding mono and di-CMPO
Figure 7.
The extraction of lanthanides(III) from 3 M HNO3 solutions
with 0.01 M solutions of compound 1 in 1,2-dichloroethane
and [bmim][Tf2N].
compounds as well as the related tripodand with the
core carbon atom. Moreover, the presence of the basic
nitrogen atom makes this ligand a a promising system
for Re(VII) extraction.
3.3. Luminescent properties
Nowadays, f-element complexes are in focus in material
science and attract growing attention due to their unique
luminescent properties defining their relevance to
luminescent systems with long lifetimes, photostability,
and line-like emission bands [45-53]. The ability of
neutral organophosphorus ligands to form strong
complexes with Ln(III) is not only of interest for practical
processing on nuclear wastes but these complexes
may subsequently find self-dependent application for
the development of novel luminescent materials. Thus,
reported are photophysical properties of complexes of
lanthanide ions, Ln(III), with a range of phosphonates
[54] including those bearing additional functionalities
such as crown ether, phthalimidomethycarboxylate,
hydroxyl, carbonyl, and amine groups attached to
phosphonic acid [55-59].
152

E. V. Sharova et al.
The tris-CMPO ligand 1 also forms strong Eu(III)
complex of 1:1 composition, Eu(L1)Cl3, which was
obtained using the reaction of the ligand with europium
trichloride in ethanol solution (see experimental). In this
complex europium coordinates three complexing arms
via O,O-bidentate coordination mode with participation
of all oxygen atoms of the phosphoryl and carbonyl
groups. Indeed, in the 31Р NMR spectrum the complex
demonstrated a singlet upfield shifted (up to 0.7 ppm)
compared to the resonance of the free ligand observed
at ca. 30 ppm. It should be noted that, in contrast to
the phosphonate analogs [58,59], europium complexes
of CMPO ligands bearing diphenylphosphoryl group
usually display a large upfield coordination shift in the
phosphorus spectra with ∆δ in the range of 12-45 ppm
depending on metal:ligand ratio [29]. This fact may be
explained by formation of more strong complexes due
to the so called effect of ‘anomalous aryl strengthening’
[60] as a coordination shift is a measure of the
coordination bond strength. The IR spectrum (KBr) of
the complex showed no absorption bands of the free
P=O and C=O groups while the intensive bands of the
metal coordinated phosphoryl and carbonyl group were
observed at 1160 cm-1 and 1625 cm-1, respectively.
First of all we estimated the luminescent properties
in a solid state of the above complexes at 300 K. All
complexes show an intensive red luminescence
characteristic for the Eu(III) ions in the coordination
compounds. The values of the luminescence intensity
(Ilum, rel. units) at the maximum of the most intensive
band at 613 nm which corresponds the supersensitive
5D0→7F2 transition, are presented in the Table 3.
Comparing the Ilum values one may note that the value
for the complex Eu(NO3)3(L5)2 is higher than that for its
analogs formed with ligand 4 with the secondary amide
group. Indeed, high-frequency oscillations of the N-H
groups (ν=3300 sm-1) are known to be quenchers of
lanthanide ion luminescence, particularly when these
groups are located close to the coordination unit. In
the case of complex Eu(L1)Cl3, in which the ligand also
possess N-H groups, the higher luminescence may
be connected with the disposition of the metal ion in
the cavity of the tripodal ligand. In such case phenyl
groups being the good photoantenna absorbing the UV-
radiation, are apparently more close to the coordination
unit. Moreover, the influence of different anions (Cl-
and NO3-) presenting in the complexes could not be
completely excluded.
Figure 8. The
effect of HNO3 concentration in the aqueous
phase on the extraction of Re(VII) by 2×10-4 M solution
of compound 1 in 1,2-dichloroethane.
Figure 9. The
effect of the concentration of extractants 1-3
in 1,2-dichloroethane on the extraction of Re(VII)
from 0.1 HCl, 0.1 M HNO3, 0.1 M HClO4, and 0.1 M H2SO4
solutions.
Nevertheless, despite variety of f-element
complexes with known CMPO derivatives have been
examined by a number of researchers and reported in
the literature [29], the data concerning their luminescent
properties, to the best of our knowledge, are absent
in the literature. Therefore, we have investigated the
luminescent behaviour in solid (Eu) and in solutions (Eu
and Tb) of some complexes formed by tripodal ligand
1 or the related mono-CMPO ligands 4, 5 differing in
the presence or absence of hydrophilic hydrogen at the
nitrogen atom of CMPO moiety. Complexation properties
towards f-elements for the ligands 4 and 5 were reported
by us previously [22]. According to the IR, multinuclear
NMR data and X-ray diffraction studies, ligand 4
forms complexes with europium nitrate of different
composition having either three or two ligand molecules
in Eu coordination sphere, namely, Eu(NO3)3(L4)3 and
Eu(NO3)3(L4)2 while ligand 5, independently on reaction
conditions, form only complex Eu(NO3)3(L5)2 of ML2
composition.
As one may expect, the luminescence of these Eu(III)
complexes is 6-16 fold weaker in ethanol solutions
(concentration 1×10-3М) than that observed for the
solid samples. In this case, complexes with the ligand
153

N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl)acetamide)] -
novel CMPO tripodand: synthesis, extraction studies
and luminescent properties of lanthanide complexes
Table 3. Luminescence intensity (Ilum) of the europium complexes in the solid state and in solution in the abs. EtOH (c= 1×10-3 М).
Ilum,* rel. units
Solution
The luminescence color visually
Eu complex
Eu(NO3)3(4)3
Solid
Solid
Solution
136
21
red
sky-blue
Eu(NO3)3(5)2
Eu(NO3)3(4)2
EuCl3(1)
215
184
217
13
17
14
red
red
red
sky-blue
sky-blue
red
* Ilum values are reduced to the unified experiment condition
Table 4. Luminescence of europium and terbium complexes in solutions with 1:10 Ln(III):L ratio (CEu,Tb = 5×10-5 M, CLig = 5×10-4 M).
Solutionsa
Tb(III)
Ilum,b rel. units
Solutionsa
Eu(III)
Ilum,b rel. units
TbCl3 + 1
TbCl3 + 4
TbCl3 + 5
100
107
116
EuCl3 + 1
EuCl3 + 4
EuCl3 + 5
30
3
5
a Ethanol in the case of ligands 4,5, and 1:1 acetonitrile-ethanol mixture for the ligand 1.
b Ilum is reduced to the unified experiment conditions.
CMPO ligands 4 and 5, the intensity of Tb(III) radiation
is 20-40 times higher than for the corresponding Eu(III)
ones and the luminescence was slightly more intensive
when the ligand had no hydrophilic NH-group. For the
complex of tris-CMPO 1, the difference in Tb(III) and
Eu(III) luminescence was significantly less (3.3 times)
(Fig. 10). It should be noted that in the related studies
on photoptical properties complexes of lanthanide ions,
Ln(III), formed in solutions by phosphonate analogs of
acetylacetonate ligands RC(O)CH2P(O)(OEt)2 (R= CH3,
Ph) [58] and diethyl(phthalimidomethyl)phosphonate
ligand [59] the more intensive luminescence was
observed in the case of the Tb-based systems.
4. Conclusions
Wavelength, nm
Figure 10. Luminescence spectra of Eu(III) (1) and Tb(III) (2)
complexes with tripodal ligand 1 in acetonitrile solution
(СEu, Tb=5×10-5 М, СLig=5×10-4 М).
The novel tripodal CMPO ligand - N-tris[(2-aminoethyl)-
2-(diphenylphosphoryl)acetamide)] was synthesized
and studied as extractant for Ln(III), alkaline-earth
cations and perrenate anion from neutral and acidic
media in comparison with the related mono- and bis-
CMPO derivatives. The effect of different additives
in the aqueous phase and that of the extractant
concentration in the organic phase on the extraction
of metal ions was considered. The stoichiometry
of the extracted complexes has been determined.
The Eu(III) and Tb(III) O,O-bidentate complexes with
4 displayed slightly higher luminescence than those
formed by ligands 1 and 5. Note, that excluding the
complex Eu(L1)Cl3, visually the sky-blue luminescence
was observed in solutions of the complexes with mono-
CMPO ligands.
Furthermore, we investigated the luminescent
properties of solutions of the complexes obtained by
mixing of the lanthanide (Tb(III) and Eu(III)) chloride with
the corresponding ligand in different ratio (six series, the
ratio M:L was equal to 1:1, 1:2, 1:3, 1:5, and 1:10). In
general, the intensity of luminescence increased with
the increase of the ligand concentration and achieved
the maxima when 10-fold excess of the ligand was used
(Table 4). For the complexes formed by the same mono-
carbamoylmethylphosphoryl
compounds
possess
intensive luminescence both in a solid state and in
solutions and some insight on the relationship structure-
luminescence properties may be of interest for further
development of luminescent materials on the base of
such compounds.
154

E. V. Sharova et al.
Acknowledgments
We are grateful to T. A. Orlova and A. E. Lezhnev for
their assistance in ICP-MS measurements.
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