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Ternary complexes of uranyl beta-diketones with aliphatic amides
Polyhedron Vol. IO, No. 14, pp. 1683-1686. 1991 Printed in Great Britain
TERNARY
0277-5387/9l $3.00+.00 0 1991 Pergamon Press plc
COMPLEXES OF URANYL BETA-DIKETONES WITH ALIPHATIC AMIDES
P. B. RUIKAR, M. S. NAGAR and M. S. SUBRAMANIAN* Radiochemistry
Division, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India (Received 9 November 1990 ; accepted 15 April 1991)
Abstract-Ternary adducts of uranyl beta-diketone chelates [beta-diketones = l-phenyl3-methyl-4-benzoyl-pyrazolone-5 l-phenyl-3-methyl-4-acetyl-pyrazolone-5 (PMBP), (PMAP) and thenoyltrifluoroacetone (TTA)] and dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) have been isolated and characterized as UO,(beta-diketone), * amide. The ‘H NMR spectra indicate the existence of restricted rotation of the C-N bond in these complexes. Evidence for the existence of the amide adducts of PMBP as an isomeric mixture has been adduced from the presence of four phenyl protons in their ‘H NMR spectra. Thermal investigations confirm the existence of two types of PMBP moieties as opposed to the TTA adducts.
Long chain aliphatic amides have potential applications in nuclear fuel processing as they have some specific advantages over the conventional extractant, viz. TBP. I-6 A detailed investigation of several amides for the separation of uranium and plutonium is contained in some excellent review articles. 7,8Amides can also act as synergistic donors in the extraction of actinides by beta-diketones. Recently, Yi Min and Wang Liyag have reported synergistic extraction of uranyl nitrate by a mixture of N,N-diisopropylbutylamide and 1-phenyl-3methyl-4-benzoyl-pyrazolone-5 (PMBP). Recently we have also investigated the synergistic extraction of uranyl ion with thenoyltrifluroacetone (TTA) and dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA).” Several binary solid complexes of actinides with amides have also been investigated by Bagnall and co-workers. “,I2 The synthesis, thermal studies, IR and ‘H NMR spectra of ternary uranyl complexes with beta-diketones such as TTA, PMBP and lphenyl-3-methyl-4-acetyl-pyrazolone-5 (PMAP) with three amides, viz. the dibutyl derivatives DBHA, DBOA and DBDA are described in this paper.
*Author to whom correspondence
should be addressed.
EXPERIMENTAL Preparation of the ligands
Pyrazolones and amides were synthesized by the methods of JensenI and Baldwin,14 respectively, and characterized by elemental analysis, IR and NMR spectra. Preparation of the complexes
The complexes were prepared by solvent extraction of aqueous uranyl nitrate solution (10 cm’, 5 mM) at pH = 2 with benzene (10 cm3) containing 10 mM of the beta-diketone and 5 mM of the amide. The organic layer was dried with anhydrous sodium sulphate, evaporated to dryness and the crude product recrystallized from n-hexane. Characterization of the complexes
The complexes were characterized by elemental analysis (Table 1) using standard semi-micro analytical methods. I5 Uranium was determined volumetrically, as well as gravimetrically, as reported earlier.16*17 IR spectra of samples in Nujol mulls between CsI discs were measured using a Pu-9510 spectrophotometer in the range 4000-200 cm-‘.
1683
1684
P. B. RUIKAR Table 1. Analytical
data of uranyl pyrazolone C (%)
Complex UOI(PMBP),.DBHA UO,(PMBP),*DBOA U02(PMBP)2-DBDA U02(PMAP),
- DBHA
U02(PMAP)2
- DBOA
U02(PMAP)2
- DBDA
U02(TTA)*
et nl.
- DBHA
U0,(TTA)2.DBOA
a Figures in parentheses ‘Volumetric. ’ Gravimetric.
H (%)
48.5 (49.1) 49.6 (50.2) 51.3 (51.0) 54.8 (54.7) 55.6 (55.5) 56.4 (56.3) 39.4 (38.3) 40.8 (39.7)
RESULTS AND DISCUSSION
IR spectra The empirical assignments of a few typical bands in the IR spectra of the complexes are given in Table 2. The reduction in the stretching frequency of the
N (%)
5.6 (5.5)
($:)
(:2) (Z)
(Z) 6.3 (6.3)
5.3 (5.4) (E)
(E) 7.4
(Z)
(7.3) 7.0
(Z)
(7.1) 1.5
(Z)
(1.5) 1.5 (1.5)
indicate calculated
‘H NMR spectra were obtained with a Varian FT80A spectrophotometer using 0.05 M solutions in d-chloroform. Thermal investigations were carried out using a ULVAC (TGD-7000) differential thermal analyser in air at a heating rate of 10°C min ’ ,
amide complexes”
c---o(v)
Py. ring v
C-H
inpl.
U (%)
25.5 26.0 (25.7) 25.0 25.0 (24.9) 24.7 24.7 (24.2) 22.6 23.2 (22.6) 22.1 22.4 (22.1) 21.7 21.5 (21.5) 24.5 25.0 (25.3) 24.1 25.4 (24.6)
values.
carbonyl band of the free amide from 1640 to 1600 cm-’ indicates its coordination in the molecule. ‘H NMR spectra The ‘H NMR spectral assignments of a few typical complexes are given in Table 3. In the complexes with TTA as the chelating agent, a broad singlet for the thienyl protons in addition to sharp singlets for the CH protons have been observed. The presence of two clear triplets for the a-CH protons of the butyl group in TTA complexes indicate their nonequivalence caused by restricted rotation of the
Table 2. Typical IR bands of uranyl beta-diketone-amide X
U (%)*
O-U-O
C-H
complexes
o/p M-O(Py)
M-O(X)
O-U-O
DBHA DBOA DBDA
1610 1610 1695
1510 1505 1495
Beta-diketone 1065 1065 1060
= PMBP ; Amide = X 775 935 772 930 765 922
430 420 420
350 350 345
275 270 265
DBHA DBOA DBDA
1600 1600 1705
1495 1495 1508
Beta-diketone 1060 1060 1070
= PMAP ; Amide = X 770 930 770 925 780 935
420 415 432
340 345 360
265 265 280
DBHA DBOA
1595 1585
= TTA ; Amide = X 795 925 790 925
495 500
360 360
260 250
Beta-diketone 1070 1070
1685
Ternary complexes of uranyl beta-diketones
Table 3. ‘H NMR spectra of (a) UO,(TTA)* - DBHA and DBOA, and (b) UO,(PMBP), - DBHA and DBOA complexes
Nature of proton
Coupling constants
Band position (ppm)
Intensityb
Multiplicity’
8.16(8.10) 7.70(7.65) 7.20(7.37) 6.71(6.65) 3.80(3.75) 3.50(3.49) 2.80(2.76) 1.70(1.65) 1.21-1.01 (1.05) 0.60(0.55)
l(1) l(l) l(1) l(1) 2(2) 2(2) 2(2) 8(8) 9 (13) 6(6)
Broad singlet Broad singlet Broad singlet Singlet Triplet Triplet Triplet Multiplet Multiplet
8.25-7.15 (8.25-7.18) 3.40(3.45) 2.50(2.53) 1.93(1.95) 1.50(1.53) 0.98( 1.OO) 0.55(0.65)
20 20 4 2 6 8 9(13) 6
Broad peak Broad peak 5 (merger of 3 triplets)
(4 Thienyl proton( 1) Thienyl proton(2) Thienyl proton(3) Proton c(-CH, of butyl( 1) a-CH, of butyl(2) a-CH, of amide Other CH, of butyl CH, and other CH, of amide CH3 of butyl (b) Phenyl and benzoyl c(-CH, of butyl LX-CH2 of amide CH3 of pyrazolone Other CH, of butyl CH3 and other CH, of amide CH3 of butyl
Triplet
3
(J)
6(4)
8 Singlet Multiplet Multiplet Multiplet
a Results in parentheses indicate values for DBOA complexes. ‘Number of protons. ‘Number of peaks.
C-N bond, the triplets arising due to the associated spin coupling by the adjacent methylene protons. Two separate signals for the N-methyl protons have also been observed in the spectra of N,Ndimethylacetamide because of their non-equivalence due to hindered rotation. Methyl protons of the butyl group are observed to be the most shielded, occuring as triplets due to coupling by the adjacent methylene protons. In the PMBP and PMAP complexes with amides, the presence of four and two separate signals, respectively, for the aromatic protons indicate their existence as a mixture of isomers. Four separate signals for the aromatic protons have also been observed in the’H NMR spectrum of U02(PMBP)2 - Hz0 in acetone. The amethylene protons of the butyl groups in PMBP and PMAP complexes have been observed as a composite peak of six lines (only five peaks observed), involving the merger of two triplets in the PMBP and PMAP complexes, whereas they are observed as two clear triplets in the corresponding TTA complexes. From this, it is clear that the PMBP and PMAP complexes are less sterically hin-
dered to rotation around the C-N with the TTA complexes.
bond compared
Thermal investigations
The results of the thermal investigations of U02(PMBP)2 complexes with DBHA and DBOA are given in Table 4. The DTA curves of these two complexes show a sharp dip at 125°C presumably due to a phase change on melting. Three plateaux corresponding to weight loss due to one PMBP, amide and the second PMBP are observed, giving rise to exothermic, endothermic and strong exothermic peaks, respectively. The loss of amide and the second PMBP molecule did not give two clear plateaux and the weight loss has been computed as corresponding to the loss of both. On the other hand, the thermograms of U02(TTA)2 - DBHA and UO,(TTA), - DBOA show only one plateau due to the loss of both TTA moieties, indicating that they are symmetrically bonded. This agrees with the idea that the amide complexes of pyrazolones exist as a mixture of isomers.
1686
P. B. RUIKAR
et al.
Table 4. Thermal data for U02(PMBP), X Molecular weight Water loss at 110°C (%) Total loss of weight (%) Loss of one PMBP (%) Decomposition temperature (“C) Peak height temperature (“C) Nature of peak Loss of PMBP+X (%) (i) Decomposition temperature (“C) Peak height temperature (“C) Nature of peak (ii) Decomposition temperature (“C) Peak height temperature (“C) Nature of peak Phase change temperature (“C)
- X complexes”
Hz0
DBHA
DBOA
844.6 3.4 68.9 (68.0) 30.9 (32.9) 280 455
1052
1080
72.2 (73.0) 26.2 (26.4) 190 310 Exothermic 47.0 (47.9) 340 410 Endothermic 450 540 Exothermic 125
72.3 (74.0) 25.9 (25.7) 210 305 Exothermic 46.4 (46.7) 340 410 Endothermic 450 570 Exothermic 125
31.2 (33.0)
380 510 Exothermic
” Figures in parentheses indicate calculated values.
Acknowledgements-The authors wish to express their grateful thanks to Dr P. R. Natarajan for his keen interest in the work.
REFERENCES 1. T. H. Siddall III, J. Phys. Chem. 1960,64, 1863. 2. G. M. Gasparini and G. Grossi, Sep. Sci. Tech. 1980, 15, 825. 3. T. H. Siddall III, J. Znorg. Nucl. Chem. 1963, 25, 883. 4. T. H. Siddall III, J. Znorg. Nucl. Chem. 1967, 29, 149. 5. K. B. Brown, C. A. Blake and J. M. Schimdt, USAEC Report ORNL-3452 (1963). 6. K. B. Brown, C. A. Blake and J. M. Schmidt, USAEC Report ORNL-3627 (1964). 7. G. M. Gasparini and G. Grossi, Solv. Ext. Zon Exch. 1986,4, 1233. 8. C. Musikas, Inorg. Chem. Acta 1987, 140, 197.
9. Yi Min and Wang Liya, Atom. Energy Sci. Tech. 1987, 21, 545. 10. R. Veeraraghavan, S. A. Pai and M. S. Subramaninan, J. Radioanal. Nucl. Chem. 1990, 141, 2, 339. 11. A. Ghany, M. Al-Daher and K. W. Bagnall, J. Less Common Metals 1985,108,257 ; 1985,109,381. 12. K. W. Bagnall and G. F. Pyne, J. Less Common Metals, 1985, 109, 31. 13. B. S. Jensen, Acta Chem. Stand. 1959,13,1668,1890. 14. W. H. Baldwin, C. E. Higgins and J. M. Schmitt, USAEC Report ORNL-3679, Chem. Technol. Div. Progr. Report, pp. 5657. Oak Ridge National Laboratory, Oak Ridge, Tennessee (1965). 15. M. S. Nagar, P. B. Ruikar and M. S. Subramanian, Report BARC- 1048 (1980) ; Report BARC- 1299 (1986). 16. M. S. Nagar, P. B. Ruikar and M. S. Subramanian. Polyhedron 1987, 6, 1913. 17. M. S. Nagar, P. B. Ruikar and M. S. Subramanian, Lanthanide Actinide Res. 1989, 3, 21.
TERNARY
0277-5387/9l $3.00+.00 0 1991 Pergamon Press plc
COMPLEXES OF URANYL BETA-DIKETONES WITH ALIPHATIC AMIDES
P. B. RUIKAR, M. S. NAGAR and M. S. SUBRAMANIAN* Radiochemistry
Division, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India (Received 9 November 1990 ; accepted 15 April 1991)
Abstract-Ternary adducts of uranyl beta-diketone chelates [beta-diketones = l-phenyl3-methyl-4-benzoyl-pyrazolone-5 l-phenyl-3-methyl-4-acetyl-pyrazolone-5 (PMBP), (PMAP) and thenoyltrifluoroacetone (TTA)] and dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) have been isolated and characterized as UO,(beta-diketone), * amide. The ‘H NMR spectra indicate the existence of restricted rotation of the C-N bond in these complexes. Evidence for the existence of the amide adducts of PMBP as an isomeric mixture has been adduced from the presence of four phenyl protons in their ‘H NMR spectra. Thermal investigations confirm the existence of two types of PMBP moieties as opposed to the TTA adducts.
Long chain aliphatic amides have potential applications in nuclear fuel processing as they have some specific advantages over the conventional extractant, viz. TBP. I-6 A detailed investigation of several amides for the separation of uranium and plutonium is contained in some excellent review articles. 7,8Amides can also act as synergistic donors in the extraction of actinides by beta-diketones. Recently, Yi Min and Wang Liyag have reported synergistic extraction of uranyl nitrate by a mixture of N,N-diisopropylbutylamide and 1-phenyl-3methyl-4-benzoyl-pyrazolone-5 (PMBP). Recently we have also investigated the synergistic extraction of uranyl ion with thenoyltrifluroacetone (TTA) and dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA).” Several binary solid complexes of actinides with amides have also been investigated by Bagnall and co-workers. “,I2 The synthesis, thermal studies, IR and ‘H NMR spectra of ternary uranyl complexes with beta-diketones such as TTA, PMBP and lphenyl-3-methyl-4-acetyl-pyrazolone-5 (PMAP) with three amides, viz. the dibutyl derivatives DBHA, DBOA and DBDA are described in this paper.
*Author to whom correspondence
should be addressed.
EXPERIMENTAL Preparation of the ligands
Pyrazolones and amides were synthesized by the methods of JensenI and Baldwin,14 respectively, and characterized by elemental analysis, IR and NMR spectra. Preparation of the complexes
The complexes were prepared by solvent extraction of aqueous uranyl nitrate solution (10 cm’, 5 mM) at pH = 2 with benzene (10 cm3) containing 10 mM of the beta-diketone and 5 mM of the amide. The organic layer was dried with anhydrous sodium sulphate, evaporated to dryness and the crude product recrystallized from n-hexane. Characterization of the complexes
The complexes were characterized by elemental analysis (Table 1) using standard semi-micro analytical methods. I5 Uranium was determined volumetrically, as well as gravimetrically, as reported earlier.16*17 IR spectra of samples in Nujol mulls between CsI discs were measured using a Pu-9510 spectrophotometer in the range 4000-200 cm-‘.
1683
1684
P. B. RUIKAR Table 1. Analytical
data of uranyl pyrazolone C (%)
Complex UOI(PMBP),.DBHA UO,(PMBP),*DBOA U02(PMBP)2-DBDA U02(PMAP),
- DBHA
U02(PMAP)2
- DBOA
U02(PMAP)2
- DBDA
U02(TTA)*
et nl.
- DBHA
U0,(TTA)2.DBOA
a Figures in parentheses ‘Volumetric. ’ Gravimetric.
H (%)
48.5 (49.1) 49.6 (50.2) 51.3 (51.0) 54.8 (54.7) 55.6 (55.5) 56.4 (56.3) 39.4 (38.3) 40.8 (39.7)
RESULTS AND DISCUSSION
IR spectra The empirical assignments of a few typical bands in the IR spectra of the complexes are given in Table 2. The reduction in the stretching frequency of the
N (%)
5.6 (5.5)
($:)
(:2) (Z)
(Z) 6.3 (6.3)
5.3 (5.4) (E)
(E) 7.4
(Z)
(7.3) 7.0
(Z)
(7.1) 1.5
(Z)
(1.5) 1.5 (1.5)
indicate calculated
‘H NMR spectra were obtained with a Varian FT80A spectrophotometer using 0.05 M solutions in d-chloroform. Thermal investigations were carried out using a ULVAC (TGD-7000) differential thermal analyser in air at a heating rate of 10°C min ’ ,
amide complexes”
c---o(v)
Py. ring v
C-H
inpl.
U (%)
25.5 26.0 (25.7) 25.0 25.0 (24.9) 24.7 24.7 (24.2) 22.6 23.2 (22.6) 22.1 22.4 (22.1) 21.7 21.5 (21.5) 24.5 25.0 (25.3) 24.1 25.4 (24.6)
values.
carbonyl band of the free amide from 1640 to 1600 cm-’ indicates its coordination in the molecule. ‘H NMR spectra The ‘H NMR spectral assignments of a few typical complexes are given in Table 3. In the complexes with TTA as the chelating agent, a broad singlet for the thienyl protons in addition to sharp singlets for the CH protons have been observed. The presence of two clear triplets for the a-CH protons of the butyl group in TTA complexes indicate their nonequivalence caused by restricted rotation of the
Table 2. Typical IR bands of uranyl beta-diketone-amide X
U (%)*
O-U-O
C-H
complexes
o/p M-O(Py)
M-O(X)
O-U-O
DBHA DBOA DBDA
1610 1610 1695
1510 1505 1495
Beta-diketone 1065 1065 1060
= PMBP ; Amide = X 775 935 772 930 765 922
430 420 420
350 350 345
275 270 265
DBHA DBOA DBDA
1600 1600 1705
1495 1495 1508
Beta-diketone 1060 1060 1070
= PMAP ; Amide = X 770 930 770 925 780 935
420 415 432
340 345 360
265 265 280
DBHA DBOA
1595 1585
= TTA ; Amide = X 795 925 790 925
495 500
360 360
260 250
Beta-diketone 1070 1070
1685
Ternary complexes of uranyl beta-diketones
Table 3. ‘H NMR spectra of (a) UO,(TTA)* - DBHA and DBOA, and (b) UO,(PMBP), - DBHA and DBOA complexes
Nature of proton
Coupling constants
Band position (ppm)
Intensityb
Multiplicity’
8.16(8.10) 7.70(7.65) 7.20(7.37) 6.71(6.65) 3.80(3.75) 3.50(3.49) 2.80(2.76) 1.70(1.65) 1.21-1.01 (1.05) 0.60(0.55)
l(1) l(l) l(1) l(1) 2(2) 2(2) 2(2) 8(8) 9 (13) 6(6)
Broad singlet Broad singlet Broad singlet Singlet Triplet Triplet Triplet Multiplet Multiplet
8.25-7.15 (8.25-7.18) 3.40(3.45) 2.50(2.53) 1.93(1.95) 1.50(1.53) 0.98( 1.OO) 0.55(0.65)
20 20 4 2 6 8 9(13) 6
Broad peak Broad peak 5 (merger of 3 triplets)
(4 Thienyl proton( 1) Thienyl proton(2) Thienyl proton(3) Proton c(-CH, of butyl( 1) a-CH, of butyl(2) a-CH, of amide Other CH, of butyl CH, and other CH, of amide CH3 of butyl (b) Phenyl and benzoyl c(-CH, of butyl LX-CH2 of amide CH3 of pyrazolone Other CH, of butyl CH3 and other CH, of amide CH3 of butyl
Triplet
3
(J)
6(4)
8 Singlet Multiplet Multiplet Multiplet
a Results in parentheses indicate values for DBOA complexes. ‘Number of protons. ‘Number of peaks.
C-N bond, the triplets arising due to the associated spin coupling by the adjacent methylene protons. Two separate signals for the N-methyl protons have also been observed in the spectra of N,Ndimethylacetamide because of their non-equivalence due to hindered rotation. Methyl protons of the butyl group are observed to be the most shielded, occuring as triplets due to coupling by the adjacent methylene protons. In the PMBP and PMAP complexes with amides, the presence of four and two separate signals, respectively, for the aromatic protons indicate their existence as a mixture of isomers. Four separate signals for the aromatic protons have also been observed in the’H NMR spectrum of U02(PMBP)2 - Hz0 in acetone. The amethylene protons of the butyl groups in PMBP and PMAP complexes have been observed as a composite peak of six lines (only five peaks observed), involving the merger of two triplets in the PMBP and PMAP complexes, whereas they are observed as two clear triplets in the corresponding TTA complexes. From this, it is clear that the PMBP and PMAP complexes are less sterically hin-
dered to rotation around the C-N with the TTA complexes.
bond compared
Thermal investigations
The results of the thermal investigations of U02(PMBP)2 complexes with DBHA and DBOA are given in Table 4. The DTA curves of these two complexes show a sharp dip at 125°C presumably due to a phase change on melting. Three plateaux corresponding to weight loss due to one PMBP, amide and the second PMBP are observed, giving rise to exothermic, endothermic and strong exothermic peaks, respectively. The loss of amide and the second PMBP molecule did not give two clear plateaux and the weight loss has been computed as corresponding to the loss of both. On the other hand, the thermograms of U02(TTA)2 - DBHA and UO,(TTA), - DBOA show only one plateau due to the loss of both TTA moieties, indicating that they are symmetrically bonded. This agrees with the idea that the amide complexes of pyrazolones exist as a mixture of isomers.
1686
P. B. RUIKAR
et al.
Table 4. Thermal data for U02(PMBP), X Molecular weight Water loss at 110°C (%) Total loss of weight (%) Loss of one PMBP (%) Decomposition temperature (“C) Peak height temperature (“C) Nature of peak Loss of PMBP+X (%) (i) Decomposition temperature (“C) Peak height temperature (“C) Nature of peak (ii) Decomposition temperature (“C) Peak height temperature (“C) Nature of peak Phase change temperature (“C)
- X complexes”
Hz0
DBHA
DBOA
844.6 3.4 68.9 (68.0) 30.9 (32.9) 280 455
1052
1080
72.2 (73.0) 26.2 (26.4) 190 310 Exothermic 47.0 (47.9) 340 410 Endothermic 450 540 Exothermic 125
72.3 (74.0) 25.9 (25.7) 210 305 Exothermic 46.4 (46.7) 340 410 Endothermic 450 570 Exothermic 125
31.2 (33.0)
380 510 Exothermic
” Figures in parentheses indicate calculated values.
Acknowledgements-The authors wish to express their grateful thanks to Dr P. R. Natarajan for his keen interest in the work.
REFERENCES 1. T. H. Siddall III, J. Phys. Chem. 1960,64, 1863. 2. G. M. Gasparini and G. Grossi, Sep. Sci. Tech. 1980, 15, 825. 3. T. H. Siddall III, J. Znorg. Nucl. Chem. 1963, 25, 883. 4. T. H. Siddall III, J. Znorg. Nucl. Chem. 1967, 29, 149. 5. K. B. Brown, C. A. Blake and J. M. Schimdt, USAEC Report ORNL-3452 (1963). 6. K. B. Brown, C. A. Blake and J. M. Schmidt, USAEC Report ORNL-3627 (1964). 7. G. M. Gasparini and G. Grossi, Solv. Ext. Zon Exch. 1986,4, 1233. 8. C. Musikas, Inorg. Chem. Acta 1987, 140, 197.
9. Yi Min and Wang Liya, Atom. Energy Sci. Tech. 1987, 21, 545. 10. R. Veeraraghavan, S. A. Pai and M. S. Subramaninan, J. Radioanal. Nucl. Chem. 1990, 141, 2, 339. 11. A. Ghany, M. Al-Daher and K. W. Bagnall, J. Less Common Metals 1985,108,257 ; 1985,109,381. 12. K. W. Bagnall and G. F. Pyne, J. Less Common Metals, 1985, 109, 31. 13. B. S. Jensen, Acta Chem. Stand. 1959,13,1668,1890. 14. W. H. Baldwin, C. E. Higgins and J. M. Schmitt, USAEC Report ORNL-3679, Chem. Technol. Div. Progr. Report, pp. 5657. Oak Ridge National Laboratory, Oak Ridge, Tennessee (1965). 15. M. S. Nagar, P. B. Ruikar and M. S. Subramanian, Report BARC- 1048 (1980) ; Report BARC- 1299 (1986). 16. M. S. Nagar, P. B. Ruikar and M. S. Subramanian. Polyhedron 1987, 6, 1913. 17. M. S. Nagar, P. B. Ruikar and M. S. Subramanian, Lanthanide Actinide Res. 1989, 3, 21.