Extraction of lanthanides(III) by phosphorylated naphthyridine ligands from carbonate solutions

Article abstract of DOI:10.1134/S0036023612010196

The extraction capacities and selectivities of 1,8-naphthyridine-based neutral organophosphorus reagents in extracting trivalent lanthanides (Ln, Nd, Ho, Yb) from carbonate solutions were studied. The length and nature of the linker between the naphthyrid

Full text of DOI:10.1134/S0036023612010196

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 1, pp. 108–114. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.M. Safiulina, O.A. Sinegribova, A.G. Matveeva, E.I. Goryunov, M.S. Grigoriev, E.E. Nifant’ev, I.G. Tananaev, 2012, published in Zhurnal Neorganꢀ
icheskoi Khimii, 2012, Vol. 57, No. 1, pp. 115–122.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Extraction of Lanthanides(III) by Phosphorylated Naphthyridine
Ligands from Carbonate Solutions
A. M. Safiulinaa, O. A. Sinegribovab, A. G. Matveevac, E. I. Goryunovc,
M. S. Grigorieva, E. E. Nifant’evc, and I. G. Tananaeva
a Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
b Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125047 Russia
c Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences,
ul. Vavilova 28, Moscow, 119991 Russia
Received September 7, 2010
Abstract—The extraction capacities and selectivities of 1,8ꢀnaphthyridineꢀbased neutral organophosphorus
reagents in extracting trivalent lanthanides (Ln, Nd, Ho, Yb) from carbonate solutions were studied. The
length and nature of the linker between the naphthyridine and phosphoryl moieties were found to have conꢀ
siderable influence on the efficiency and selectivity of lanthanide extraction.
DOI: 10.1134/S0036023612010196
Recycling spent nuclear fuel and analyzing sewage
and oils in fuel disposal places still remain topical. The
PUREX process and TRUEX process, aqueous methꢀ
ods which are based on the extraction recovery of
EXPERIMENTAL
Materials and reagents. Solutions were prepared
using bidistilled water, chloroform (reagent grade),
Arsenazo III (analytical grade); Na2CO3
6H2O, Nd(NO3)3 6H2O, and NaCl were
of reagent grade; and Ho(NO3)3 6H2O, and
Yb(NO3)3 6H2O were of pure grade. Dibenzoꢀ18ꢀ
⋅
10H2O,
nuclear fuel components from nitric acid solutions, La(NO3)3
⋅
⋅
⋅
have been in greatest use for separating and preconꢀ
centrating transplutonium and rareꢀearth elements.
Both processes employ neutral monoꢀ and bidentate
organophosphorus compounds as extraction agents
[1–3]. The rapidly developing in recent years carbonꢀ
ate method (CarbEx process) provides processing
spent nuclear fuel by means of extraction from carꢀ
bonate solutions using quaternary ammonium salts as
extractants [4]. To our knowledge, biꢀ and polydentate
neutral organophosphorus compounds have not been
tested for use in extraction from carbonate solutions.
For monodentate phosphorus compounds, it is well
known that they do not extract lanthanides and
actinides from carbonate solutions [5, 6]. However,
1,8ꢀnaphthyridineꢀbased neutral phosphorylated
ligands, which virtually do not extract actinides and
lanthanides from nitric acid solutions, can quite sucꢀ
cessfully recover trivalent lanthanides from carbonate
solutions [7].
⋅
crownꢀ6 (from Aldrich) was used as received.
1H and 31Р{1H} NMR spectra of ligands were
recorded on Bruker Avance TMꢀ400 (the working freꢀ
quency was 400.13 and 161.98 MHz, respectively) in
0.05 M solutions in CDCl3 or DMSOꢀd6; the internal
reference for 1H NMR spectra was signals from residꢀ
ual protons of the deuterated solvents; the external refꢀ
erence for the 31Р{1H} NMR spectra was 85% H3PO4
.
2ꢀ[2ꢀ(Diphenylphosphoryl)ethyl]ꢀ1,8ꢀnaphthyriꢀ
dine (I) was prepared as described earlier [8].
2ꢀ(Diphenylphosphorylamido)ꢀ5,7ꢀdimethylꢀ1,8ꢀ
naphthyridine (II) was synthesized by an improved
procedure. A solution of 1.24 g (5.25 mmol) of dipheꢀ
nylchlorophosphinate in 5 mL of absolute chloroform
was added droppwise to a mixture of 0.87 g (5 mmol)
of finely divided 5,7ꢀdimethylꢀ2ꢀaminoꢀ1,8ꢀnaphthyꢀ
1
ridine, 0.60 g (6 mmol) of absolute triethylamine,
30.5 mg (0.25 mmol) of 4ꢀdimethylaminopyridine,
and 10 mL of absolute chloroform under stirring on a
Our goal was to study the extraction of trivalent
lanthanides of the cerium subgroup (lanthanum and
neodymium) and the yttrium subgroup (holmium and
ytterbium) from carbonate solutions by two naphthyꢀ
ridine ligands that differ from each other in the length
and nature of the linker between the naphthyridine
core and the diphenylphosphoryl group.
1
2ꢀAminoꢀ5,7ꢀdimethylꢀ1,8ꢀnaphthyridine was synthesized by a
known procedure [9] and purified by crystallization from ethaꢀ
1
nol–dimethylformamide; mp = 221.5–222.5°C. H NMR
spectrum (DMSOꢀd , d, ppm, J, Hz): 2.47 (s, 3H, 5ꢀCH ); 2.48
6
3
(s, 3H, 7ꢀCH ); 6.64 (br.s, 2H, NH ); 6.75 (d, 1H, H
(3),
3
2
naphth
(4),
naphth
3
3
J
J
= 8.8); 6.89 (s, 1H, H
(6)); 8.03 (d, 2H, H
H–H
H–H
naphth
= 8.9).
108

EXTRACTION OF LANTHANIDES(III)
109
magnetic stirrer, and the mixture was stirred at room bration time was verified by increasing the phase conꢀ
temperature until a homogeneous solution was tact time to 120 min, distribution ratios did not
formed.
The solvent and excess triethylamine were removed
in vacuo (~15 Torr); the residue was washed with water
(3 20 mL) and dried in vacuo over Р2О5 (110 , 2 h,
change. Phase separation was accomplished by cenꢀ
trifugation. After phase separation, concentration of
lanthanides in the aqueous phase were determined
spectrophotometrically [11]. For each concentration,
five independent experiments were carried out. All
×
°С
~1 Torr). Yield: 1.77 g (95%). The product was
obtained as a light yellow fineꢀcrystalline substance.
Mp = 210–211.5°C (chloroform–hexane 1 : 2). Literꢀ
experiments were carried out at 20
1°С.
Na+ determination in the organic phase after
extraction of neodymium(III) from a carbonate solution
(0.078 mol/L) was carried out by flame atomicꢀemission
spectrometry (the detection limit was 10–10 g/mL) [12].
Calibration solutions of NaCl in water and in chloroꢀ
form (in the presence of dibenzoꢀ18ꢀcrownꢀ6) were
prepared by a volumetric–gravimetric method. Preꢀ
liminarily, the ligand solutions in chloroform and the
organic phase of a model experiment (extraction in the
absence of a lanthanide salt in the aqueous phase) were
2
ature data: mp= 191–193°C [7, 10] .
For C22H20N3OP (FW = 373.39 g/mol) anal. calcd, %:
C, 70.77; H, 5.40; N, 11.25; P, 8.29.
Found, %: C, 70.47; H, 5.47; N, 11.09; P, 8.35.
1H NMR spectrum (CDCl3
(s, 3H, 5ꢀCH3); 2.58 (s, 3H, 7ꢀCH3); 6.93 (s, 1H,
naphth(6)); 7.16 (d, 1H, Hnaphth(3), 3JH–H = 9.1); 7.43
(td, 4H,
ꢀС6Н5, 3JH–H = 7.3 Hz, 4JH–P = 2.1); 7.49 (t,
2H, ꢀC6H5 +
ꢀC6H5, 3JH–H = 7.3); 7.85–7.97 (m, 5H,
Hnaphth(4)).
31P{1H} spectrum (CDCl3,
1H NMR spectrum (DMSOꢀd6
,
δ, ppm, J, Hz): 2.49
H
m
verified for the absence of trace Na+
.
p
о
Xꢀray crystallography. Transparent crystals of
naphthyridine monohydrate II suitable for Xꢀray crysꢀ
tallography were obtained by the isothermal evaporaꢀ
tion at room temperature of a solution of the comꢀ
pound in chloroform. Colorless crystals of
C22H22N3O2P (II) (FW = 391.450) are monoclinic; at
δ, ppm): 21.2 br.s.
,
δ
, ppm, , Hz):
J
2.48 (s, 3H, 5ꢀCH3); 2.50 (s, 3H, 7ꢀCH3); 7.06 (s, 1H,
Hnaphth(6)); 7.26 (d, 1H, Hnaphth(3), 3JH–H = 9.2); 7.49
3
4
(td, 4H,
7.53 (t 2H,
ꢀC6H5 3JH–H = 7.1, 3JH–P = 12.1 Hz; 8.20 (br.d, 1H,
Hnaphth(4)).
31P{1H} NMR spectrum (DMSOꢀd6,
16.8 br.s.
mꢀС6Н5, JH–H = 7.0 Hz, JH–P = 2.3 Hz);
100(2) K, a = 15.239(3)
8.1009(18) = 115.954(5)
group Cc
Å
°
,
,
b
V
= 17.953(3)
Å, c =
3
p
ꢀC6H5, JH–H = 6.9 Hz); 7.84 (dd, 4H,
Å
Z
,
β
= 1992.7(7) Å3, space
о
,
= 4, ρcalc = 1.305 g/cm3. An experimental
array of 18 611 reflections was collected on a Bruker
Kappa Apex II automated fourꢀcircle diffractometer
δ
, ppm):
equipped with an area detector (Mo
K radiation, a
α
The solutions were prepared by a volumetric–
gravimetric method. The concentrations of sodium
carbonate solutions were refined by potentiometric
titration with 0.1 M HCl (standard solution). Lanthanide
nitrate solutions were prepared by dissolving weighed
portions of nitrates in 0.01 M nitric acid. The concentraꢀ
tions of lanthanide nitrate solutions (0.001 mol/L) were
refined spectrophotometrically as described in [11] on
a Cary50 Scan (Varian) spectrometer.
graphite monochromator,
from a singleꢀcrystal chip 0.40
size. After averaging equivalent reflections, a total of
4193 unique reflections were obtained (Rint = 0.0498)
to be further used in solving and refining the structure.
The structure was solved by a direct method; all nonꢀ
ϕ
ꢀ
and
×
ω
ꢀscans) at 100 K
0.20 0.06 mm in
×
2
hydrogen atoms were refined for
in the anisotropic
Fhkl
approximation. The water hydrogen atoms were
located from difference electron density syntheses and
refined isotropically without any constraint. The
hydrogen atoms of the NH, CH, and CH3 groups were
positioned in geometrically calculated positions and
refined with isotropic temperature parameters, which
were 1.2 Ueq of an N or C atom for NH and CH,
respectively, and 1.5 Ueq of a C atom for CH3. The
SHELXTL program package [13] was used in all calꢀ
culations. The final refinement values were as follows:
pH of solutions for extraction was measured on
pH/ion Analyzer Radelkisꢀ125, model ORꢀ300, with
an accuracy of 0.01 pH units. The electrode pair was
calibrated against standard buffer solutions with pH of
1.68, 4.01, and 9.22 (at 20°С).
Extraction experiments. To a groundꢀstoppered
test tube was added 1.5 mL of water or a sodium carꢀ
bonate solution (0.104 or 0.473 mol/L), 0.5 mL of a
0.001 M solution of a metal nitrate, and 2 mL of 0.01 M
solution of a ligand in chloroform. pH of solutions for
extraction was 2.71, 10.67, and 10.89, respectively.
Phases were stirred for 20 min. The extraction equiliꢀ
R1 = 0.0483 (over Fhkl for 2173 reflections with
I >
Fh2kl
2σ(I)), wR2 = 0.1041 (over for all reflections);
GOOF = 1.018. The data collection completeness was
96.8%; the number of refined parameters was 261; and
the maximal and minimal residual peaks were 0.264
and –0.315 e Å–3, respectively. The Flack parameter
x,
2
Lemport et al. [10] were also mistaken in indicating CDCl
3
instead of DMSOꢀ
d as the solvent used for recording NMR
6
spectra for ligand
I.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 1 2012

110
SAFIULINA et al.
C(19)
C(13)
C(14)
C(16)
C(12)
C(11)
C(23)
C(24)
C(17)
C(18)
C(22)
C(21)
C(36)
N(1)
C(15)
C(35)
C(34)
N(2)
N(3)
P(1)
C(31)
C(20)
C(25)
C(26)
O(1)
C(33)
C(32)
O(1W)
Fig. 1. Molecular structure of naphthyridine II monohydrate. Thermal displacement ellipsoids are given with 50% probability.
Hydrogen atoms are imaged by spheres of arbitrary radius. Hydrogen bonds are shown by dashed lines.
which equals 0.03(14), validates the adequacy of absoꢀ
lute structure determination [14].
O
O
N
N
P
N
The complete tables of atomic coordinates, bond
lengths, and bond angles are available from the Camꢀ
bridge Structural Database (CCDC code: 785052).
P
N
NH
I
II
RESULTS AND DISCUSSION
Naphthyridine
I was prepared as described in [8];
for naphthyridine II, the synthesis procedure was
improved. The reaction of 2ꢀaminoꢀ5,7ꢀdimethylꢀ2ꢀ
aminoꢀ1,8ꢀnaphthyridine and diphenylchlorophosꢀ
phinate in the presence of triethylamine as a hydrogen
chloride scavenger was carried out in the presence of
catalytic amounts of 4ꢀ(dimethylamino)pyridine
(DMAP) (Scheme 1). The use of this catalyst allowed
the process to be carried out at room temperature and
the target product yield to be increased appreciably
(up to 95%).
The ligands under study, namely, 2ꢀ[2ꢀ(dipheꢀ
nylphosphoryl)ethyl]ꢀ1,8ꢀnaphthyridine (I) and 2ꢀ
(diphenylphosphorylamido)ꢀ5,7ꢀdimethylꢀ1,8ꢀnaphꢀ
thyridine (II), which differ from each other in the
length and nature of the linker between the naphthyriꢀ
dine moiety and diphenylphosphoryl group, are
potentially tridentate ligands, which are capable of
being coordinated to lanthanide cations with formaꢀ
tion of stable complexes [15–17].
CH3
CH3
Ph P(O)Cl, Et N, DMAP
3
2
CH3
N
N
NH2
CH3
Scheme 1.
N
N
NHP(O)Ph2
II
Inasmuch as the melting temperature of the naphꢀ mined the structure of our synthesized compound
thyridine II synthesized by this procedure was nearly using Xꢀray crystallography (Fig. 1). The bond lengths
20°С
higher than reported earlier [7, 10], we deterꢀ and bond angles fall within the ranges typical of the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 1 2012

EXTRACTION OF LANTHANIDES(III)
111
) in
Table 1. Selected bond lengths (
d
) and bond angles (
ω
relevant class of compounds [18] (Table 1). The naphꢀ
thyridine ring N(2)N(3)C(11)–C(18) is planar; the
atoms depart from the plane of the ring by 0.03(1) Å on
the average. Noteworthy, the P(1)N(1)C(11) moiety lies
the structure of the naphthyridine II monohydrate
Bond , Å Angle , deg
1.481(3) O(1)P(1)N(1) 116.92(16)
1.674(3) O(1)P(1)C(21) 111.58(18)
d
ω
virtually in the plane of the naphthyridine ring: torsion P(1)–O(1)
angles P(1)N(1)C(11)N(2) and P(1)N(1)C(11)C(12)
are –6.2(4)° and 175.1(3)°, respectively. On the
whole, the geometric parameters of the compounds
are close to those found earlier for related phosphoryꢀ
lated 1,8ꢀnaphthyridines, namely, 2ꢀ[2ꢀ(dipheꢀ
nylphosphoryl)ꢀ2ꢀmethylpropyl]ꢀ1,8ꢀnaphthyridine
[8] and 5,7ꢀdimethylꢀ2ꢀ(diethoxyphosphorylamido)ꢀ
1,8ꢀnaphthyridine [10].
P(1)–N(1)
P(1)–C(21) 1.807(4) N(1)P(1)C(21) 106.21(17)
P(1)–C(31) 1.808(4) O(1)P(1)C(31) 111.79(17)
N(1)–C(11) 1.402(5) N(1)P(1)C(31) 103.55(17)
N(1)–H(1)
0.88
C(21)P(1)C(31) 105.92(17)
C(11)N(1)P(1) 121.8(3)
C(11)N(1)H(1) 119.1
Xꢀray crystallography shows that naphthyridine II
single crystals contain solvation water molecules, each
being involved in three strong intermolecular hydroꢀ
gen bonds (Fig. 2, Table 2). The proton acceptors in
these bonds are a phosphoryl oxygen atom and one of
the nitrogen atoms (N8) of the naphthyridine core; the
NHꢀgroup is the proton donor in the Hꢀbond with the
oxygen atom of a water molecule (Table 2). As a result,
hydrogen bonds link naphthyridine II and water molꢀ
ecules into chains that run in the direction [101] of the
crystal (Fig. 2).
P(1)N(1)H(1)
119.1
The extraction capacity of naphthyridine ligands
I
and II was studied in the extraction of lanthanum(III),
neodymium(III), holmium(III), and ytterbium(III)
into the organic phase from dilute nitric acid solutions
(pH 2.71) and carbonate solutions.
Distribution ratios (D = [Ln(III)]org/[Ln(III)]aq,
where [Ln(III)] is the overall concentration of all speꢀ
0
b
a
Fig. 2. Fragment of the naphthyridine II monohydrate crystal structure: a chain viewed along the axis c. Hydrogen bonds are
shown by dashed lines.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 1 2012

112
SAFIULINA et al.
Table 2. Hydrogen bond geometry (
d
, Å and
ω
, deg) in the naphthyridine monohydrate II structure
D–H···A
D–H
H···A
D···A
∠
(DHA)
O(1W)*–H(1A)···O(1)
O(1W)*–H(1B)···N(3)
N(1)–H(1)···O(1W)*
0.95(5)
0.87(5)
0.88
2.08(5)
2.01(5)
2.10
2.936(4)
2.867(5)
2.857(5)
150(4)
169(4)
144
*
Symmetry transformation for O(1W):
x
+ 1/2, –
y
+ 1/2,
z
+ 1/2.
cies containing Ln(III) in the corresponding phase) distribution ratios for lanthanum, holmium, and ytterꢀ
were measured at fixed concentrations of the extractꢀ bium are almost independent of the sodium carbonate
ant (0.01 mol/L in chloroform) and the lanthanide concentration in the range from 0.078 to 0.355 mol/L,
(0.001 mol/L in the aqueous phase). The results of for neodymium the extraction coefficient decreases
these experiments are displayed in Figs. 3 and 4 as strongly (by a factor of 3.5) as the concentration
plots of the distribution ratios versus sodium carbonate increases.
concentration.
Unlike ligand I, ligand II also has a noticeable selecꢀ
tivity to the lanthanides studied. The separation factor for
the (La + Nd)/(Ho + Yb) groups in 0.078 mol/L sodium
One can see from Fig. 3 that the naphthyridine
ligand
I with the ethylene linker extracts lanthanide
carbonate solution is rf = 5–6 (rf
= DLn/DHo for the
cations rather poorly, although lanthanum(III) and
neodymium(III) are extracted a little better than holꢀ
mium(III) and ytterbium(III). For all lanthanides,
distribution ratios are virtually independent of the
aqueous phase composition.
La/Ho pair and so on). In 0.355 mol/L sodium carꢀ
bonate solution, lanthanum can be separated from
neodymium, holmium, and ytterbium: the separation
factor for the La/Nd pair is ~3, and for the La/(Ho +
Yb) group, about 10–15 (see Fig. 4).
It is known that trivalent lanthanides and actinides
exist in carbonate solutions in the form of various carꢀ
bonate complexes [19, 20]. For americium(III), comꢀ
plexes of composition [Am(CO3)]+ are dominant speꢀ
cies even at near neutral pHs while an excess of carꢀ
bonate ions exists in solution; at pH of about 8.5 (ionic
strength of 0.1 mol/L), the dominant species are
[Am(CO3)]+ and [Am(CO3)2]– in almost equal conꢀ
Ligand II, which has the NHꢀlinker, extracts lanꢀ
thanides far better. Distribution ratios for all lanꢀ
thanides studied are one to two orders of magnitude
higher than for ligand I (Fig. 4). As for ligand I, here
the cerium subgroup lanthanides (lanthanum(III) and
neodymium(III)) are extracted better than the yttrium
subgroup lanthanides (holmium(III) and yttrium(III)).
However, unlike for ligand
ferent pattern of the effect of the sodium carbonate
I, here we observe the difꢀ
concentration on the extraction of lanthanides. While centrations. At higher pHs, the dominant species are
D
0.30
D
20
0.25
0.20
0.15
0.10
0.05
15
10
5
La
La
Nd
Ho
Nd
Ho
Yb
Yb
0
0.1
0.2
cNa CO , mol/L
0.3
0.4
0
0.1
0.2
cNa CO , mol/L
0.3
0.4
3
2
3
2
Fig. 3. Lanthanide(III) distribution ratios versus sodium
Fig. 4. Lanthanide(III) distribution ratios versus sodium
carbonate concentration in extraction with a 0.01 mol/L
solution of ligand II in chloroform.
carbonate concentration in extraction with a 0.01 mol/L
solution of ligand I in chloroform.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 1 2012

EXTRACTION OF LANTHANIDES(III)
113
[Am(OH)2]+ and [Am(CO3)2]– [19, 20]. Lanthanide
−
= {[LnLm(NO3)2]+
}
org
NO3
complexes of similar compositions are described in the
literature [21], but they are studied in a less detailed
manner than actinide complexes [22, 23]. Data
obtained for americium(III) were used for further anaꢀ
n
= 0–2, m = 1–2
Scheme 3.
Comparing these equations we see that, given equal
(or close) extractabilities of the complex to the organic
phase, extraction from carbonate solutions should be
more efficient than from nitric solutions, for the reaꢀ
son that extractable carbonate complexes contain
twice lanthanide atoms per neutral species than in
nitrate complexes.
3
lyzing carbonate solutions of lanthanides.
Because of considerable Na+ concentrations, lanꢀ
thanideꢀcontaining complex cations and anions and
Na+ containing compounds can both be transferred
with neutral compounds to the organic phase in
extraction from carbonate solutions. However, no
traces of Na+ were found in the organic phase after
extraction of neodymium(III) from a carbonate soluꢀ
tion (0.078 mol/L) (flame atomicꢀemission spectromꢀ
Noteworthy, the numbers of ligand molecules in
extracted complexes can be different for reagents
II as judged from the data available for nitrate comꢀ
plexes. For ligand , for example, complexes of comꢀ
positions Ln : L 1 : 1 and 1 : 2 have been isolated and
characterized [25], while for ligand II only complexes
of composition 1 : 2 have been prepared under similar
conditions [15].
I and
I
eter; the detection limit is 10–10 g/mL [12]). Thus, the
suggested compositions of extracted lanthanide comꢀ
4
plexes is [LnLk(CO3)]+
·
[LnLl(CO3)2]–, and in the
range of higher pHs and higher sodium carbonate conꢀ
centrations, [LnLm(OH)2]+ [LnLn(CO3)2]–, where
and are likely to be 1 or 2.
Presumably, the scheme of lanthanide extraction
·
k,
As regards denticities of ligands
I and II in
extracted complexes, we might expect them to be the
same as in similar complexes of lanthanide nitrates.
According to Xꢀray crystallography and vibration
spectroscopy, in cationic and neutral complexes of
lanthanides nitrates with 2ꢀphosphorylꢀsubstituted
1,8ꢀnaphthyridines, the ligands have tridentate ONN
coordination involving the phosphoryl oxygen atom
and both nitrogen atoms of the naphthyridine core,
and this coordination mode is retained in polar solꢀ
vents as shown by NMR and IR spectroscopy [15–17,
l,
m,
n
from carbonate solutions is as follows (coordinated
water molecules are omitted):
−
+
L n C O
(
)
]
+
Ln CO
3
+ (k
+
l)Lorg
[
(
)
]
[
3
aq
2
aq
= {[LnLk(CO3)]+[LnLl(CO3)2]–}org
+
−
+
+ (n + m)Lorg
Ln OH
Ln CO
3
(
)
(
)
]
[
]
[
2
2
aq
aq
25, 26]. Accordingly, ligands I and II are likely to be
tridentate when being complexed in dilute nitric acid
and carbonate solutions, too.
= {[LnLn(OH)2]+[LnLm(CO3)2]–}org
= 0–2
k, l, n, m
The linker length between the coordination sites of
a bidentate ligand is known to appreciably affect the
complexation and extraction properties of the ligand
[27, 28]. The review [27] analyzes the extraction
capacities of bidentate ligands as a function of linker
length. Ligands having the methylene linker between
the two functional groups have higher extraction
capacities than those having the ethylene linker, and as
the linker length increases further, the extraction
capacity decreases. And despite the fact that in ligands
Scheme 2.
Evidently, for different lanthanides the composiꢀ
tions and contents of complex species in the aqueous
phase will be dictated by their own equilibrium conꢀ
stants [23, 24], and the lipophilicity of neutral species
with hydroxo and carbonato cations can be different.
Accordingly, these features should be reflected in the
variation of distribution ratios as a function of carbonꢀ
ate ion concentration and pH, and these dependences
will be individual for each lanthanide.
I
and II, linkers between the naphthyridine moiety
In dilute nitric acid, lanthanides mainly exist in the
form of [Ln(NO3)2]+ and [Ln(NO3)]2+, and their
extraction may be described by the following scheme
(coordinated water molecules are omitted):
and the P(O) group have different natures (–NH–
and –CH2CH2–, respectively), the decrease in
extraction capacity with increasing linker length is well
pronounced here. The nitrogen of the imide linker is
not involved in coordination to the metal [15].
Further, conditions have been found for providing
lanthanide reꢀextraction from a saturated organic
phase. By the example of neodymium(III), reꢀextracꢀ
tion was accomplished by 0.05 M HNO3 from a satuꢀ
rated organic phase obtained upon neodymium(III)
extraction by a solution of ligand II in chloroform.
Under these conditions, the degree of neodyꢀ
mium(III) recovery reaches ~90%, which proves that
reꢀextraction is virtually complete.
3−n +
(
)
−
+ (3 –
n)
+ mLorg
a q
N O 3
Ln NO
(
)
]
[
3
n
aq
= [LnLm(NO3)3]org
3−n +
NO−
(
)
+ (3 –
n)
+ mLorg
3 w
Ln NO
(
)
]
[
(
)
3
n
aq
3
4
Neodymium(III) frequently serves as a model for studying the
behavior of trivalent actinides [20].
One of the counterions of the extracted species can be free of
extractant L molecules.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 1 2012

114
SAFIULINA et al.
8. P. S. Lemport, G. V. Bodrin, M. P. Pasechnik, et al.,
In summary, our study of the extraction of trivalent
lanthanides from dilute nitric acid and carbonate soluꢀ
tions by phosphorylated naphthyridine ligands and II
to chloroform has demonstrated a high extraction
Russ. Chem. Bull. 56 (9), 1911 (2007).
9. J. Bernstein, B. Stearns, E. Shaw, and W. A. Lott, J. Am.
I
Chem. Soc. 69, 1151 (1947).
ability of ligand II with an NHꢀlinker in carbonate 10. P. S. Lemport, E. I. Goryunov, A. V. Vologzhanina,
et al., Russ. Chem. Bull. 58 (7), 1445 (2009).
11. S. B. Savin, Arsenazo III (Atomizdat, Moscow, 1966)
solutions. The maximum extraction efficiency for this
ligand to lanthanum and neodymium is observed in
decimolar sodium carbonate solutions; the distribuꢀ
tion ratio reaches 16–19 (the degree of recovery is 94–
95% in one stage). Ligand II also has a certain selecꢀ
tivity to the cerium and yttrium subgroups elements.
[in Russian].
12. Yu. A. Zolotov, Fundamentals of Analytical Chemistry.
Chemical Analyses (Vyssh. shkola, Moscow, 2002) [in
Russian].
Ligand I with an ethylene linker between the naphthyꢀ 13. G. M. Sheldrick, Acta Crystallogr., Sect. A 64, 112
(2008).
ridine and phosphoryl moiety virtually does not
extract lanthanides from the tested solutions; the disꢀ
tribution ratio does not exceed 0.25. The change in the
nature of linker appreciably changes the extraction
efficiency and selectivity of phosphorylated naphthyꢀ
ridine ligands in carbonate and lowꢀacidity solutions.
14. H. D. Flack, Acta Crystallogr., Sect. A 39, 876 (1983).
15. A. G. Matveeva, P. S. Lemport, A. V. Vologzhanina,
et al., Proceedings of the 24th International Chugaev
Conference on Coordination Chemistry (St. Petersburg,
2009), p. 320 [in Russian].
16. A. G. Matveeva, P. S. Lemport, A. S. Peregudov, et al.,
Proceedings of the 24th International Chugaev Conferꢀ
ence on Coordination Chemistry (St. Petersburg, 2009),
p. 321 [in Russian].
17. A. G. Matveeva, P. S. Lemport, A. S. Peregudov, et al.,
Proceedings of the 15th International Conference on
Chemistry of Phosphorus Compounds (St.ꢀPetersburg,
2008), p. 54 [in Russian].
ACKNOWLEDGMENTS
The authors are grateful to G.V. Bodrin (Candidate
of Chemistry) and P.S. Lemport (Candidate of Chemꢀ
istry) for providing the 2ꢀ[2ꢀ(diphenylphosphoꢀ
ryl)ethyl]ꢀ1,8ꢀnaphthyridine (I) sample.
This study was supported by the Presidential grant
Program for young scientists (grant no. MKꢀ
3658.2009.3) and by the Presidium of the Russian
Academy of Sciences (Fundamental Research Proꢀ
gram No. 7 “Development of Methods for Preparing
Chemicals and Materials Design”).
18. F. H. Allen, O. Kennard, D. G. Watson, et al., J. Chem.
Soc., Perkin Trans. II, S1 (1987).
19. D. L. Clark, D. E. Hobart, and M. P. Neu, Chem. Rev.
95, 25 (1995).
20. G. Meinrath and J. I. Kim, Radiochim. Acta 52/53, 29
(1991).
21. S. I. Stepanov and A. M. Chekmarev, Extraction of
RareꢀEarth Metals by Salts of Quaternary Ammonium
Bases (IzdAT, Moscow, 2004) [in Russian].
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