Synthesis and properties of Np(VI) and Pu(VI) monophthalates

Article abstract of DOI:10.1007/s11137-005-0002-0

Neptunium(VI) and plutonium(VI) monophthalates were prepared and characterized. The complexes AnO₂ (COO)₂C ₆H₄·2H₂O were isolated from cold solutions, and AnO₂ (COO)₂C₆H ₄·1.33H₂O, from hot solutions. NpO₂ (COO)₂C₆H₄ b. 2H₂O and PuO ₂ (COO)₂C₆H₄·2H₂O crystalize in the triclinic and monoclinic systems, respectively. The complexes AnO₂(COO)₂C₆H₄·1.33H ₂O are isostructural and crystallize in the rhombohedral system. The thermal behavior of these complexes was studied. Their IR and electronic absorption spectra were recorded. The properties of these complexes were compared to those of known U(VI) monophthalates.

Full text of DOI:10.1007/s11137-005-0002-0

Radiochemistry, Vol. 46, No. 5, 2004, pp. 421 428. Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 389 395.
Original Russian Text Copyright 2004 by Krot, Bessonov, Grigor’ev, Charushnikova, Makarenkov.
Synthesis and Properties of Np(VI) and Pu(VI) Monophthalates
N. N. Krot, A. A. Bessonov, M. S. Grigor’ev,
I. A. Charushnikova, and V. I. Makarenkov
Institute of Physical Chemistry, Russian Academy of Sciences, Moscow, Russia
Received October 7, 2003
Abstract Neptunium(VI) and plutonium(VI) monophthalates were prepared and characterized. The com-
plexes AnO (COO) C H 2H O were isolated from cold solutions, and AnO (COO) C H 1.33H O, from
2
2
6
4
2
2
2
6
4
2
hot solutions. NpO (COO) C H 2H O and PuO (COO) C H 2H O crystalize in the triclinic and monoclin-
2
2
6
4
2
2
2
6
4
2
ic systems, respectively. The complexes AnO (COO) C H 1.33H O are isostructural and crystallize in
2
2
6
4
2
the rhombohedral system. The thermal behavior of these complexes was studied. Their IR and electronic
absorption spectra were recorded. The properties of these complexes were compared to those of known U(VI)
monophthalates.
Compounds of hexavalent actinides with anions of
on VP-1AP anion exchanger. Pu(C O ) 6H O was
2 4 2 2
ortho-phthalic acid, o-C H (COOH) (H L), are poor-
precipitated from the eluate. The precipitate was
6
4
2
2
ly studied. UO nH O with n = 1 [1] and 2 and 0 [2]
treated with a hot equimolar mixture of HClO and
2
2
4
were synthesized and partially characterized. The crys-
tal structure of the mixed-ligand phthalate urea com-
plex [UO L(OC(NH ) )] 0.5H O was established [3].
HNO until decomposition of oxalate anions was com-
3
plete. The solution was evaporated to wet salts, which
were dissolved in 4 M HNO + 2 M HClO . The
2
2 2
2
3
4
No data on the composition, structure, and properties
of Np(VI) and Pu(VI) phthalates were reported. How-
ever, it is of scientific interest to compare these com-
plexes in the U Np Pu series. In this work we studied
the behavior of Np(VI) and Pu(VI) in phthalate solu-
tions, as well as crystallization of compounds formed
in these systems. The compounds AnO L nH O
resulting 0.1 0.2 M Pu solution was used as a stock
solution. Aliquots of this solution were evaporated to
wet salts when necessary. The working Pu(VI) solu-
tion with pH 2 4 were prepared from these residues
and used for no more than 4 days. The plutonium
valence was monitored by the absorption in the range
400 900 nm.
2
2
(
An = Np and Pu) were prepared and characterized.
ortho-Phthalic acid (analytically pure grade) was
purified by the following procedure. A weighed por-
These data were compared with those for uranium
analogs.
tion of H L was dissolved in a stoichiometric amount
2
of 2 M KOH. The solution was filtered through a
dense paper filter and acidified with an equimolar
EXPERIMENTAL
amount of HNO . The potassium biphthalate precipi-
tate was vacuum-filtered through a glass frit, washed
with water, and dissolved in a small excess of am-
3
We used weakly acidic (pH 2 3) 0.1 0.5 M solu-
tions of uranyl nitrate, neptunyl nitrate, and plutonyl
perchlorate. Uranium was purified as follows. Am-
monium uranyl tricarbonate was precipitated. The pre-
cipitate was converted to U O by calcination. The
monia. Finally, the solution was acidified to pH
2
with HNO . The precipitate was vacuum-filtered,
3
thoroughly washed with water, and dried at 70 80 C
to constant weight. Working 0.5 1.0 M LiHL and
3
8
resulting uranium oxide was dissolved in HNO . The
3
solution was evaporated to wet salts, which were kept
for 3 days in a desiccator over KOH granules. The dry
residue was dissolved in water. Neptunium was puri-
fied by the anion-exchange procedure followed by
precipitation of Np(C O ) 6H O. The precipitate
Li L solutions were prepared from stoichiometric
2
amounts of H L and LiOH.
2
Other solutions were prepared by the conventional
procedures from chemically pure grade compounds
and distilled water.
2
4 2
2
was treated with hot concentrated HNO . The solution
3
Electronic absorption spectra were recorded on a
Shimadzu UV-3110 spectrometer (Japan); and IR
spectra, on a Specord M80 spectrometer.
was evaporated to wet salts, which were kept in a
desiccator over KOH granules. The dry residue was
dissolved in water. Plutonium-239 was purified as fol-
lows. Plutonium(IV) was sorbed from 7.5 M HNO3
Powder X-ray diffraction patterns were obtained
1
066-3622/04/4605-0421 2004 MAIK Nauka/Interperiodica

422
KROT et al.
70 C. Reduction of Np(VI) and Pu(VI) was monitored
by the growth of the Np(V) absorption band at 980
990 nm and by a decrease in the Pu(VI) absorption
at 830 850 nm.
In preliminary experiments, we found that Np(VI)
and Pu(VI) solutions turned yellow after addition of
lithium phthalate (Li L). This is due to strong and
2
broad charge-transfer bands of Np(VI) and Pu(VI)
phthalate complexes in the short-wave UV region
(
Fig. 1). As expected theoretically [11, 12], the charge-
transfer band of the neptunyl complexes is slightly
shifted to the visible region as compared to the pluto-
nium band. This is due to the fact that the standard
potential of the Np(VI)/Np(V) couple (1.24 V) is
higher than that of the Pu(VI)/Pu(V) couple (1.02 V)
[13]. As a result, the color of neptunyl solutions is
more intense than that of plutonyl solutions, all other
conditions being the same.
Fig. 1. Absorption spectra of Np(VI) and Pu(VI) in phtha-
3
2
late solutions. (a) [Np(VI)] = 2.60 10 M; [L ], M:
3
3
3
(
(
1
1) 0, (2) 1.65 10 , (3) 3.30 10 , and (4) 8.25 10 .
3
2
b) [Pu(VI)] = 1.90 10 M; [L ], M: (1) 0, (2) 1.02
3
3
2
0 , (3) 3.42 10 , and (4) 1.45 10 .
By the analogy with the oxalate solutions [4, 8, 9],
we suggest formation of AnO L complexes at low
2
phthalate concentrations and transformation of these
complexes into anionic species at higher ligand con-
centrations. This assumption was experimentally con-
firmed. As seen from Fig. 2, when the Li L concen-
2
tration increases, the intensity of the main absorption
band at 831 nm in the spectrum of hydrated PuO2
+
2
ions decreases and a new band at 840 nm appears
simultaneously. The presence of the isobestic point
indicates that the PuO L complex prevails in solutions
2
with [Pu(VI)] : [Li L] molar ratio < 1 : 1. This com-
plex is relatively stable, since its yield is close to
Fig. 2. Transformation of the main plutonium absorption
2
band with increasing Li L concentration. [Pu(VI)] = 1.9
2
3
3
100% at the equimolar concentration of phthalate
1
(
(
0
M; [Li L] 10 , M: (1) 0, (2) 0.51, (3) 1.02, (4) 1.51,
2
5) 2.00, (6) 2.47, (7) 5.01, (8) 7.57, (9) 12.32, and
10) 17.33.
anions. At higher [Li L], the intensity of the plutonyl
2
monophthalate band decreases, and a new band ap-
pears at 845 nm. The presence of the second isobestic
with a Guinier focusing camera (CuK 1 radiation, Si
point in the examined range of Li L concentrations
2
as internal reference). The samples were weighed on
a Sartorius microbalance (1 g sensitivity). Thermal
analysis curves were recorded on a Q 1500D Paulik
Paulik Erdey derivatograph (Hungary) interfaced with
a computer.
suggests formation of a single new complex, probably
2
PuO L .
2
2
The intensity of coloration of Np(VI) and Pu(VI)
phthalate solutions remains the same for at least
2
days. This indicates relatively high stability of nep-
tunyl and plutonyl in phthalate solutions in the cold.
The absorption spectra of Pu(VI) solutions containing
RESULTS AND DISCUSSION
LiHL and Li L slightly change on heating at 70 C
2
Np(VI) and Pu(VI) are gradually reduced in oxalate
solutions at room temperature to the pentavalent state
for 1 h. However, in hot Li L solutions, the main
2
plutonyl band is substantially shifted to the short-
wave region. This is likely due to rearrangement of
the plutonium coordination sphere. However, to con-
firm this assumption, additional studies are required.
[4 6]. However, oxalate complexes of Np(VI) and
Pu(VI) were prepared [4, 7 10]. Taking this fact into
account, prior to the preparative work we studied
semiquantitatively the complexation and stability of
plutonyl and neptunyl in solutions with different con-
Neptunium(VI), unlike Pu(VI), is gradually reduced
in phthalate solutions at 70 C. The reduction rate in
2
centrations of HL and L anions in the cold and at
RADIOCHEMISTRY Vol. 46 No. 5 2004

SYNTHESIS AND PROPERTIES OF Np(VI) AND Pu(VI) MONOPHTHALATES
423
Li L solutions is 5 7%/h. In LiHL solutions, the
(IV). Weighed portions 26.144 and 2.272 mg. Found
2
reduction is accelerated by a factor of 2. The fact that
the stability of neptunyl in hot phthalate solutions is
lower than that of plutonyl is obviously due to the dif-
PuO 59.06 and 58.93%. Calculated PuO 59.04%.
2
2
Thus, the composition and structure of neptunyl
phthalates and plutonyl phthalates precipitated from
cold solutions and solutions heated at 70 C differ.
This is clearly confirmed by the results of powder
X-ray diffraction analysis.
2
+
+
ference in the potentials of the AnO /AnO couples.
2
2
Thus, PuO L nH O and NpO L nH O can be
2
2
2
2
prepared by addition of equimolar amounts of phtha-
late anions to weakly acidic solutions of Pu(VI) and
Np(VI) at room temperature or at mild warming. First,
we studied precipitation of these compounds from
cold solutions under the above conditions. 0.1 M
PuO (ClO ) and NpO (NO ) solutions remain trans-
The X-ray pattern of compound I precipitated from
cold solution is similar to that of UO L 2H O (V)
2
2
[
2], erroneously indexed in the rhombic system. We
also indexed the X-ray pattern of V [14] and refined
its unit cell parameters [15] in the triclinic system
2
4 2
2
3 2
parent for a certain period after addition of an equi-
(Table 1). Compound II, unlike I and V, crystallizes
molar amount 0.5 M Li L at room temperature. Crys-
2
in the monoclinic system (Table 2). Possible space
groups are C2/c and Cc. The refined unit cell param-
eters are summarized in Table 3.
tal druses appeared on the tube walls only in several
hours. Grinding of these crystals and stirring of the
solution substantially accelerated the crystallization.
Slow crystallization process suggests that these com-
pounds are polymers. The precipitation was virtually
complete in 2 days, although the mother liquor re-
mained yellow, probably due to noticeable solubility
of the compounds in water. The precipitates were
filtered off through a glass filter under a vacuum,
thoroughly washed with water, and dried in an air
flow for 3 h. To analyze the products, they were cal-
cined at 800 850 C to the corresponding dioxides.
Compounds III and IV precipitated from hot solu-
tions are isostructural and differ in the structure from
I and II. The X-ray pattern of III, indexed in the
rhombohedral system (possible space groups are R3
and R3) is presented in Table 4. It should be noted
that compound V precipitates from both cold and hot
solutions. After heating at 175 C for 20 h, the precipi-
tate transformes into UO L 1.33H O (VI) isostruc-
2
2
tural with III and IV. Monohydrate UO L H O
2
2
prepared by us in accordance with the procedure in [1]
turned out to be the dihydrate. We obtained single
crystals of II, III, and V suitable for single crystal
X-ray diffraction analysis. These structural data will
be published later.
The results of gravimetric analysis were consistent
with the general formula AnO L 2H O (An = Np or
2
2
Pu). NpO L 2H O (I). Weighed portions 33.732 and
2
2
1
.215 mg. Found NpO 57.00 and 57.24%. Calculated
2
NpO 57.36%. PuO L 2H O (II). Weighed portions
0.384 and 2.486 mg. Found PuO 57.20 and 57.62%.
Calculated PuO 57.54%.
2
2
2
3
2
We studied the synthesized compounds by thermal
analysis. The results are shown in Fig. 3. Compound I
is exothermally dehydrated at 80 105 C. The anhydr-
ous product is stable up to 270 C. At 270 315 C,
it endothermally decomposes to form pentavalent
species. Decomposition at higher temperature is a
complex process involving Np(V) reduction and oxi-
dation of phthalate anions to CO and H O. Thermal
2
Precipitation of neptunyl phthalates and plutonyl
phthalates from hot solutions differs from that from
cold solutions. 0.05 0.15 M Np(VI) or Pu(VI) solu-
tions containing equimolar amounts of Li L become
2
turbid after heating at 70 C for several minutes. Then,
dark brown large hexagonal pyramidal or prismatic
crystals appear on the walls. The crystallization is
complete in 2 3 h. The solution remains colored prob-
ably owing to noticeable solubility of these com-
pounds. Sometimes, when Pu(VI) solutions are heated
for a short time, large elongated prismatic crystals of
an impurity phase are formed. The products were
filtered off through a glass frit under a reduced pres-
sure, washed with water, and dried in an air flow for
2
2
decomposition is completed above 550 C to form
finally NpO2.
Since anhydrous NpO L is stable in a wide tem-
2
perature range, we prepared this compound by heating
I at 115 C for 30 min. Inasmuch as the product was
X-ray amorphous, we failed to compare its structure
with the powder X-ray diffraction pattern of the urani-
um analog [2]. It should be specially noted that the
dehydration temperature of I (100 C) is lower than
that of V (140 C). Hence, crystallization water in the
structure of I is bound more weakly than in the struc-
ture of V.
3
h. Gravimetric analysis showed that the composition
of both compounds is described by the general formula
AnO L 1.33H O. NpO L 1.33H O (III). Weighed
2
2
2
2
portions 30.901 and 2.158 mg. Found NpO 58.89 and
5
2
9.40%. Calculated NpO 58.86%. PuO L 1.33H O
2 2 2
RADIOCHEMISTRY Vol. 46 No. 5 2004

424
KROT et al.
Table 1. Experimental and calculated powder X-ray diffraction patterns of UO L 2H O (V)
2
2
dexp
,
I/I , %
dcalc
,
hkl
dexp
,
I/I , %
dcalc
,
hkl
0
0
7
6
6
6
5
5
5
5
4
4
4
4
4
4
4
3
3
3
.848
.702
.397
.048
.856
.733
.202
.139
.972
.823
.598
.507
.446
.051
.016
.920
.843
.809
100
30
30
60
60
60
10
60
30
60
60
30
60
30
30
30
30
30
7.838
6.698
6.387
6.040
5.856
5.731
5.214
5.144
4.969
4.822
4.603
4.508
4.446
4.051
4.016
3.919
3.844
3.809
010
011
100
101
011
110
111
002
101
111
012
102
111
012
112
020
021
120
112
111
112
121
021
003
022
103
211
210
201
200
122
112
113
3.054
2.994
2.978
2.881
2.830
10
10
10
30
30
3.052
2.993
2.978
2.880
2.831
2.828
2.796
2.782
2.779
2.740
2.722
2.697
2.675
2.673
2.637
2.620
2.620
2.607
2.586
2.585
2.572
2.551
2.540
2.540
2.484
2.482
2.472
2.454
2.452
2.431
2.424
2.422
122
013
211
201
113
221
211
103
023
122
210
221
212
130
203
031
131
222
104
213
004
014
123
123
202
114
032
113
031
114
132
213
2.794
2.781
5
30
2.740
2.722
2.697
2.674
5
10
10
10
2.640
2.620
30
10
2.605
2.585
5
10
3
.808
3
3
3
3
3
3
3
3
.764
.664
.578
.500
.431
.347
.333
.269
30
10
5
30
10
10
5
3.764
3.665
3.579
3.504
3.429
3.349
3.335
3.272
2.572
2.549
2.541
5
5
5
2.484
5
30
2.474
2.454
5
30
3
.268
3
3
3
.252
.193
.073
5
60
60
3.255
3.194
3.070
2.431
2.423
30
30
3
3
.069
.069
The TG and DTA curves of II are similar to those
of I (Fig. 3). The only difference is that the dehydra-
tion product of II is stable in a narrower tem-
perature range. It starts to decompose at 190 C and
then is exothermally reduced to the pentavalent spe-
cies at 230 C. Formation of the final product, PuO2,
is complete at about 560 C.
respectively. Hence, the coordination polyhedron of
plutonium in the crystal structure of II and IV is a
pentagonal bipyramid, which is similar to that in
hydrated PuO2 ion [16]. It should be noted that the
+
2
band in the spectrum of IV is shifted by 6 nm to the
long-wave region as compared to the band of Pu(VI)
monophthalate in solutions. This is clearly due to
greater number of coordination bonds and higher
strength of these bonds in the solid state. The long-
wave shift of the band of II is smaller (2 nm). Similar
trend was observed with neptunyl carboxylates, sul-
fates, and oxalates [17 20] and with plutonyl oxalates
The thermal behavior of III and IV is similar
(
Fig. 3). They do not undergo endothermic dehydra-
tion. Their active thermolysis starts above 200 C.
Formation of the final thermolysis products, AnO , is
2
complete at about 600 C.
[10]: the smaller the number of crystallization water
The electronic absorption spectra of II and IV re-
corded in NaCl pellets (Fig. 4) contain strong and
sharp bands of f f transitions at 842 and 846 nm,
molecules, the greater the long-wave shift of the f f
transition band. In this case the coordination bonds of
the dioxo cation become stronger in going to com-
RADIOCHEMISTRY Vol. 46 No. 5 2004

SYNTHESIS AND PROPERTIES OF Np(VI) AND Pu(VI) MONOPHTHALATES
425
Table 2. Experimental and calculated powder X-ray diffraction patterns of PuO L 2H O (II)
2
2
dexp
,
I/I , %
dcalc
,
hkl
dexp
,
I/I , %
dcalc
,
hkl
0
0
9
7
6
5
5
5
5
5
5
4
4
4
4
4
4
3
3
3
3
.62
.59
.51
100
30
20
10
20
30
30
40
50
20
30
30
30
60
40
30
10
5
9.67
7.58
6.52
002
110
112
112
020
113
200
021
202
004
022
114
202
023
204
221
114
115
221
024
223
311
312
131
222
132
204
116
314
223
225
133
315
041
116
224
117
402
226
135
400
316
2.611
2.562
2.506
10
10
10
2.612
2.560
2.508
2.505
2.498
2.500
2.472
2.431
2.434
2.423
2.422
2.422
2.413
2.414
2.403
2.378
2.365
2.366
2.344
2.303
2.298
2.286
2.262
2.233
2.221
2.207
2.207
2.198
2.186
2.163
2.134
2.125
2.126
2.103
2.102
2.091
2.093
2.075
2.074
2.041
2.035
042
331
314
225
333
043
135
422
227
421
118
208
402
240
242
420
241
044
243
421
335
242
136
137
045
028
318
118
243
119
512
513
150
151
316
514
423
046
137
337
515
.521
.425
.379
.297
.226
.182
.830
.728
.422
.248
.153
.072
.839
.793
.704
.607
5.531
5.426
5.372
5.292
5.224
5.179
4.833
4.731
4.423
4.243
4.151
4.073
3.841
3.797
3.703
3.606
2.498
10
2.470
2.432
10
10
2.424
10
2.412
10
2.402
2.380
2.364
10
10
10
10
2.342
2.306
2.298
2.287
2.263
2.234
2.221
2.209
10
10
10
10
10
10
10
10
3
.609
3
3
3
.534
.431
.409
5
5
15
3.534
3.437
3.413
3
.415
3
3
3
3
3
3
2
2
2
.344
.310
.216
.160
.096
.047
.962
.932
.867
20
30
20
20
20
10
10
10
10
3.343
3.306
3.214
3.161
3.097
3.051
2.965
2.933
2.869
2.198
2.185
2.165
2.136
2.125
10
10
10
10
10
2
.687
2.107
2.092
2.076
10
10
10
2
2
2
2
2
2
2
2
.804
.763
.746
.717
.685
.663
.646
.633
10
10
10
20
10
20
10
10
2.801
2.766
2.746
2.719
2.686
2.665
2.646
2.634
2.043
2.035
10
10
Table 3. Unit cell parameters of U(VI), Np(VI), and Pu(VI) monophthalates
3
Compound
a,
b,
c,
, deg
, deg
, deg
V,
V
I
II
VI
III
IV
6.733(3)
6.715(3)
10.885(4)
30.54(4)
30.44(3)
30.44(7)
8.147(3)
8.136(4)
10.852(4)
30.54(4)
30.44(3)
30.44(7)
10.574(3)
10.593(4)
19.880(9)
5.850(3)
5.861(9)
5.857(4)
95.03(3)
94.97(3)
90
90
90
100.81(3)
100.49(3)
103.50(1)
90
90
90
103.71(3)
103.71(3)
90
120
120
548.2(4)
547.7(4)
2283(2)
4725(9)
4703(10)
4699(15)
90
120
RADIOCHEMISTRY Vol. 46 No. 5 2004

426
KROT et al.
Table 4. Experimental and calculated powder X-ray diffraction pattern of NpO L 1.33H O (III)
2
2
dexp
,
I/I , %
dcalc
,
hkl
dexp
,
I/I , %
dcalc
,
hkl
0
0
1
5.34
.77
.57
70
70
50
50
10
100
10
100
10
30
30
15.22
8.79
7.61
110
300
220
101
211
131
401
321
051
241
511
710
431
161
701
351
621
900
012
2.822
2.813
2.730
5
10
10
2.823
2.811
2.734
2.730
2.720
2.678
2.647
2.637
2.562
2.537
2.502
2.500
2.500
2.438
2.404
2.368
2.313
2.313
2.287
271
122
470
811
312
042
731
232
502
660
10.1.0
191
651
390
10.0.1
612
072
532
262
8
7
5
5
4
4
4
3
3
3
3
.718
.054
.562
.380
.208
.912
.787
.679
.487
5.721
5.052
4.573
4.380
4.209
3.920
3.796
3.683
3.492
2.720
2.676
2.645
2.637
2.570
2.535
2.498
50
50
10
50
5
5
50
30
3
.485
3
3
.313
.164
30
30
3.316
3.169
2.442
2.407
2.368
2.311
30
5
30
30
3
.169
3
2
2
.096
.930
.910
70
5
5
3.102
2.930
2.913
2.288
30
pounds with lower water content. In addition, the
molar absorption coefficient of solid plutonyl phtha-
lates II and IV, estimated by the procedure in [17,
that of hydrated plutonyl cations. The fact that the
extinction coefficient of the solid plutonyl phthalates
(250 l mol 1 cm ) is similar to that of the mono-
phthalate complex in a solution suggests the structural
1
18], is lower by a factor of approximately two than
Fig. 3. TG and DTA curves of Np(VI) monophthalates I and II (weighed portions 33.732 and 30.384 mg, respectively) and Pu(VI)
1
monophthalates III and IV (weighed portions 30.901 and 26.144 mg, respectively), recorded at a heating rate of 5 deg min
.
RADIOCHEMISTRY Vol. 46 No. 5 2004

SYNTHESIS AND PROPERTIES OF Np(VI) AND Pu(VI) MONOPHTHALATES
427
complex owing to structural features of these com-
1
pounds. As a result, two bands at 940 and 928 cm
for VI and III and at 940 and 932 cm 1 for IV appear
in this spectrum range.
The IR spectra of these compounds are complicated
by the presence of the bands of carboxy groups and
benzene ring and by hydrogen bonding. However, full
interpretation of the IR spectra was beyond the scope
of this work.
Thus, crystallization and structure of Np(VI) mono-
phthalates differ from those of Pu(VI) monophthalates
and especially from those of U(VI) analogs. This is
also the case for An(VI) compounds with tetrahedral
Fig. 4. Electronic absorption spectra of crystalline
1) PuO L 2H O and (2) PuO L 1.33H O.
(
anions XO2 (X = S, Se, Mo, Cr) [21]. This difference
2
2
2
2
4
should be taken into account in preparation of new
neptunyl and plutonyl compounds.
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1
2
3
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2
2
2
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1
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1
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2
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RADIOCHEMISTRY Vol. 46 No. 5 2004