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Solvent extraction of zirconium and hafnium III. Extraction and complex formation with tridentate organophosphorus compounds
Journal of the Less-Common Metals, 59 (1978) 101 - 110 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
101
SOLVENT EXTRACTION OF ZIRCONIUM AND HAFNIUM III. EXTRACTION AND COMPLEX FORMATION WITH TRIDENTATE ORGANOPHOSPHORUS COMPOUNDS
P. BRONZAN and H. MEIDER Ruder BoskouiC Institute, Zagreb (Yugoslavia) (Received October 31, 1977)
Summary
The tridentate organophosphorus compounds bis [ (diphenylphosphinyl) methyl] phenylphosphine oxide (RPPh), bis[ (diphenylphosphinyl)methyl] phosphinic acid (RPOH) and bis[(diphenylphosphinyl)methyl] ethyl phosphinate (RPOEt) have been used for studies of zirconium and hafnium extraction from chloride, perchlorate and sulphate solutions. The formation of M(ClO&* BRPPh, M(ClO&* BRPOEt, M(ClO&. BRPOH, MC14.2RPPh, MC14. BRPOH, MC14*RPOEt, MS04( RPOH), and MS04( RPOH)z. RPOH complexes in the organic phase (M = Zr or Hf) is proposed. The extraction mechanism is discussed. The complexes Zr(OH)zCls~L~8HzO, Hf(OH)zCls*L*8HaO, ZrCII*L and [Zr(OH),(L)] (C104)s*8H20 (L = RPPh, RPOEt or RPOH) were isolated and characterized. The characteristic frequencies of the P=O, P-O-(M) and ClO, vibrations have been assigned.
1. Introduction
The extraction of zirconium and hafnium and the formation of their complexes with organophosphorus compounds have been studied by a number of authors [ 11. Our previous investigations gave evidence of the extraction of zirconium and hafnium and the formation of their complexes with some bidentate organophosphorus compounds [2, 31. There is no previous work dealing with metal complexes or solvent extraction using ligands containing three P=O groups bridged by methylene groups. This work was undertaken in order to gain information relating to the solvent extraction and complex formation properties of ligands with the general formula
102 RI C6H5\
,CH2\
,CH2\
RI = C,H,
(RPPh)
R1=OH
(RPOH)
,C6H5
RI = 0C2H5 (RPOEt) These ligands differ only in the radical RI bound to the central phosphorus atom. Depending on the nature of RI, the ligand is a phosphine oxide (RPPh), a phosphinic acid (RPOH) or a phosphinate (RPOEt). These ligands were first prepared by Maier [ 41 and by Kabachnik and his coworkers [ 51. Kabachnik and his coworkers also prepared the mono- and b&potassium salts of the ligands and proposed a mesomeric structure for the anion. Further, they proposed that the bi- potassium salt consists of two systems with delocalized bonds in different planes. The central phosphoryl group at the intersection of the planes is not equivalent to the other two. The same authors demonstrated, in perchlorate systems, hydrogen bridge formation through two oxygens. The third oxygen is not involved in hydrogen bridge formation [6] . We have also studied the effect of the radical RI on the extraction of zirconium and hafnium and on complex formation. The results obtained are given in this paper.
2. Experimental 2.1. Reagents Bis[(diphenylphosphinyl)methyl] phenylphosphine oxide (RPPh), bis[(diphenylphosphinyl)methyl] phosphinic acid (RPOH) and bis[diphenylphosphinyl)methyl] ethyl phosphinate (RPOEt) were prepared by the method used by Kabachnik et al. [5] . Radioactive 32P labelled ligands were prepared using 32PC13 (Radiochemical Centre, Amersham) as a reagent in their synthesis. Chloroform (Merck p.a.) was used without further purification as the organic solvent in the extraction experiments. Nitrobenzene for use in conductivity measurements was purified by the method of Taylor and Kraus 171. 2.2. Standard metal solutions, radioactive tracers and distribution measuremen ts The procedures used to obtain distribution data, standard metal solutions and radioactive tracers have been outlined in our earlier studies [l] .
103
2.3. Preparation of complexes The ligands, diluted in absolute ethanol, were added to an ethanolic solution of ZrCl,, ZrOCls*&HsO, ZrO(C10&*8HzO or HfOClz*8HsO. The 1igand:metal ratio was at least 1~1. The complexes were precipitated with diethylether. The precipitates were filtered and washed once with dry petroleum ether (b.p. 60 - 80 “C). The complexes precipitated were always of the same stoichiometry. 2.4. Physical measurements The molecular conductance of a millimolar solution of each complex in nitrobenzene was determined on a Tacussel conductivity bridge, type Cd 7. Potentiometric measurements were carried out on a pH meter (Radiometer PHM 64). The IR spectra of the complexes and ligands were recorded with a Perkin-Elmer 257 spectrophotometer (4000 - 625 cm-‘). Osmometric measurements were carried out with a Mechrolab osmometer, model 301 A.
3. Results and discussion 3.1. Ligand properties Because of the rather difficult preparation of the,ligands and the short half-life of the 32P isotope, only a few investigations of the distribution properties of the ligands could be carried out. The dependence of the ligand distribution on the hydrogen ion and ligand concentrations was studied. The partition of the ligands between chloroform and aqueous solutions containing 4 M H‘C104 or 0.1 M H’( [H’, Na+, ClO,] = 1 M) has been studied at various ligand concentrations. Distribution ratios obtained in these systems for the ligands RPPh and RPOEt were rather high (D > 200) and did not depend on ligand concentration. Data obtained for RPOH are given in Table 1. At concentrations higher than 10m3 M the distribution ratio increases with increasing ligand concentration. This result suggests that dimerisation occurs in this concentration range. TABLE
1
Extraction of RPOH from solutions into chloroform
[H’]
= 0.1 M, [H’,
Na+, ClO,]
= 1 M and 4 M HClOd aqueous
W’OHI (W
04 MHC10,
D[H+I =O.lM
5.0 2.5 1.25 6.25 3.12 1.56
4.54 3.14 3.03 2.19 2.09 2.33
20.30 16.85 13.75 13.72 11.74 11.42
x10-3 x1O-3 X 1O-3 X 1O-4 x 1O-4 x 1O-4
DRPOE~ and D~pph under the same conditions
are greater
than 200.
104 TABLE 2 Extraction of RPOH and RPOEt from [H’, Na+, CHaCOO-] chloroform
= 1 M aqueous solutions into
W+Ls (M)
&POH
Dw’oEt
7.1 6.5 5.9 8.9 8.5 2.4
20.4 15.1 10.8 7.7 2.4 1.4
194 108 91 80 72 63
x10-3 X lo-* x 10-5 x10-6 x 10-7 x lo-’
TABLE 3 Extraction of RPOH from [H+, Na+, ClOJ aqueous solutions into chloroform
= 1M
W+l, (W
DRPOH
2.0 1.4 6.4 1.3 3.2 1.6
9.4 13.8 19.3 28.1 26.8 22.8
x10-l x10-l x 10-2 x 1O-2
Tables 2 and 3 show the dependence of the distribution ratios of the ligands on the hydrogen ion concentration. The extraction was carried out from aqueous solutions ([Na*, H’, CH3COO-] = 1 M or [Nd, H’, ClOJ = 1 M, respectively) into chloroform. For the ligands RPOH and RPOEt, a decrease in the value of D with decreasing H’ concentration was observed for acetate/chloroform systems. The distribution of RPPh does not depend on the H’ concentration. On carrying out the extraction from perchlorate solutions with the ligand RPOH, an inverse effect was observed. For the other two ligands, D values higher than 200 were obtained in the H’ concentration range investigated. The decrease of D aron with increasing H’ concentration in perchlorate systems is a consequence of the formation of perchlorate adducts which are more soluble than the free ligand in aqueous solutions. Species formed in perchlorate systems were investigated by two-phase titration of the organic phase after equilibration of the ligand-chloroform solutions with perchloric acid. Table 4 shows the data obtained for the titration of RPPh. The results obtained indicate the formation of 1:l adducts up to 4 M HC104. At higher concentrations, the formation of 1: 2 adducts cannot be excluded. As the two-phase titration could be carried out only at ligand concentrations higher than 10m2 M, the aggregation of the perchlorate species has to be taken into
105 TABLE 4 Extraction
of HC104 into chloroform solutions (2 X lop2 M RPPh) [HC1041.,, W)
0.2 0.4 0.75 1.0 1.5 2.0 4.0 6.0 8.0
2.1 8.3 1.1 3.2 5.6 1.0 1.9 2.0 2.5
x 10-5 x 1O-5 x10-3 x 1O-3 x 1O-3 x 10-2 x 10-2 x 10-2 x 1O-2
account; this suggests that the approach used by Goffart [ 81 and Banks [ 91 is of rather limited application. For this reason the constants have not been calculated. Two-phase titration gave an indication of the species formed in the organic phase, and osmometric measurements were therefore carried out. For species isolated from perchloric acid solutions ( [HC104] > 4 M) molecular weights M higher than 1000 have been obtained, because of the aggregation of the isolated complexes. The data show monomeric RPOEt and RPPh and dimeric RPOH molecules in chloroform (MRm, talc. 554, expl. 600; Mar,,, , talc. 522, expl. 584; MaPOH, talc. 494, expl. 850). Hydrochloric and sulphuric acids are poorly extracted with the ligandchloroform solutions. The ligand RPOH is a phosphinic acid and it was of interest to determine its dissociation constant. A value of 2.64 + 0.02 for the pK was obtained by potentiometric titration from aqueous 1 M NaC104 solutions. 3.2. Zirconium and hafnium extraction The distribution ratios of zirconium and hafnium as a function of the ligand concentration are given in Fig. 1. The extraction was carried out from aqueous 4 M HC104 and 4 M HCl solutions, respectively. Some deviation from a straight line was observed for the perchloric acid/chloroform systems. This is explained by the aggregation of perchlorate adducts of the ligands. Since the ligands are not able to form adducts with HsSO4 and HCl, no deviation from straight lines for the extraction of the metals from sulphuric and hydrochloric acid solutions was observed. The high D values obtained for the extraction of the metals from perchlorate solutions are explained by the formation of rather stable complexes and the fact that perchlorate, which is a large ion with the charge smeared over the surface, is easily extracted into the organic phase. The distribution ratios as a function of ligand and HSO, concentration for the extraction of the metals from 3 M HsSO4 and [H’, Na+, ClO,,
106
3
1
1
OC
x -1
-2
-3
Fig. 1. The dependence of the extraction of Zr (0, A, 0, 0) and Hf (a, A, l, +) from 4 M HClO4 (0, 0, A, A) and 4 M HCl(0, n, 0, +) solutions on the concentration of RPPh (0, 0, D, m) or RPOEt (A, A, 0, +)_
HSOZJ = 1 M aqueous solutions, respectively, are given in Figs. 2(a) and 2(b). For the extraction of the metals with RPPh and RPOEt, low D values (D < 10b3) were obtained; these are not shown. The 1igand:metal ratios for the extraction of the metals by all three ligands and the HSO;;:metal ratio for extraction by RPOH from the systems investigated are presented in Table 5. Low metal concentrations (10m6 M) exclude polymerization. Unhydrolysed M4* species are predominant in solutions of the acidity examined [lo]. For the extraction of the metals from perchloric acid solutions the following equilibria are proposed: G f HC104 M4+ + nL-HClO
4
[ML,] ‘+ + 4[ClO4]
+
L-HC104
F=
[MLJ4*
e
[ML,] [C104] 4
(1) + nHC104
(L = RPOEt, RPPh, RPOH; n = 2 or 3 for the ligands RPPh and RPOEt, 2 for RPOH).
(2) (3) 1 or
107
I -4
'o9[RKlHI
I ,.
I -3
v
log[ Ha4-] (b)
Fig. 2. (a) The dependence of the extraction of Zr (0) and Hf (m) from 3 M HzS04 solutions on the concentration of RPOH. (b) The dependence of the extraction of Zr (0) and Hf (m) on HSOp concentration. [H’, Na+, ClO,, HSOZ] = 1 M; [RPOH] = 1 x lo-* M.
TABLE 5 Extraction of zirconium and hafnium with RPPh, RPOEt and RPOH Composition of the aqueous phase
4 M HC104 4MHCl 3 M H2SO4
HSOr/metal ratio
Ligand/metal ratio RPPh
RPOEt
RPOH
RPOH
Zr
Hf
Zr
Hf
Zr
Hf
2.8 1.8 -
2.3 2.0 -
2.5 1.2 -
2.7 1.0 -
1.3 1.6 2.6
1.5 1.5 2.2
[H+, Na+, ClO,, HSOZ] = 1 M
Zr
Hf
1.8
1.5
The shapes and slopes of the extraction curves obtained are in agreement with the results obtained for the extraction of the metals by bidentate organophosphorus compounds [ 2, 31. The conductivity measurements on the chloride species isolated (which are discussed below) indicate that the probability of extraction of dissociated species is low. On the basis of the extraction data, the formation of MC14*RPOEt, MC14-2RPPh and MC14* nRPOH (n = 1 or 2) complexes in the organic phase is proposed (M = Zr or Hf).,
108
All these results indicate that the most stable complexes are formed with the figand RPOH. With this ligand the extraction could be carried out even from aqueous 3 M HaSO4 solutions. Depending on the composition of the aqueous phase, a reaction releasing one or two HSO, ions (Fig. Z(b)) takes place, indicating that MS04(RPOH)s and MS04(RPOH)s * RPOH are formed.
Tetrachioride, oxychloride and oxyperchlorate complexes of zirconium and oxychloride complexes of hafnium have been isolated from ethanolic solutions by precipitation with diethylether. The analytical data shown in Table 6 suggest certain stoichiometries but do not reflect the real structure of the complexes. Because of the low solubihty of the complexes, we were not able to determine their molecuiar weights. Water dedication by the TABLE 6 Analytical data for zirconium and hafnium complexes with RPPh, RPOEt and RPOH Compound
ZrC14*RPPh Zr(OH)$YgRPPh*8H# ]Zr(OH)~(RPPh)](ClO4)~~8H~O Hf(OH)~C~~~~Ph*8~2~ ZrClg RPOEt Z~OH)~~i~*RPOEt*8H~# [Zr(OH)g(RPOEt)](ClC&*8H~O Hf( OH)&12*RPOEt- 8HzC ZrCl4* RPOH Zr(OH)&‘la* RPOH- 8H# ~Z~O~)~(~OH)I(C~O~)Z~~H~O Hf(OH)~C~~~RPUH- 8H20
Calculated (%)
Found (W)
M
P
CI
11.59 10.21 8.93 18.19 12.09 10.58 9.22 18.80 12.55 10.94 9.49 19.38
11.81 10.40 9.09 9.47 12.31 10.78 9.39 9.79 12.78 11.14 9.66 10.09
18.02 7.93 6.94 7.23 16.78 8.23 7.16 7.41 19.51 8.50 7.37 7.79
H20
16.13 14.09 14.67 18.70
14.02 15.17 17.26 14.94 15.63
M
P
Cl
12.07 11.10 9.82 18.75 12.95 11.39 10.05 19.52 13.35 11.30 10.28 19.92
11.32 10.54 9.14 952 12.74 11,08 9-28 9.50 12.56 Il.58 10.35 10.53
17.61 7.82 7.53 7.15 18.14 8.48 7.28 7.10 17.92 9.27 6.95 6.37
Hz
15, 14. a 15, 14. a 16. 14. a
M = Zr or Hf. aBecause only small amounts of the hafnium complexes were available, the water content of these compounds has not been determined.
Karl Fischer method and thermo~~~e~c rne~u~rnen~ indicated the presence of eight molecules of water per metal atom, Water is released over a wide temperature interval, indicating that the water molecules are bound in more than one way. The conductivity measurements given in Table 7 were carried out in nitrobenzene. The chloride and oxychloride complexes of the metals are nonelectrolytes. Values of 14 - 20 for 10m3 M solutions of the perchlorate complexes were obtained. As the IR spectra show no coordination of the perchlorate ion, the low activity of the perchlorate ion in nitrobenzene solution can be explained by the formation of highly charged polymeric metal-hydroxy-ligand complexes which exert an attractive force on
109
TABLE 7 Conductivity
data for the chloride
and perchlorate
complexes
of zirconium
Compound
and
hafnium
&I (10-3M)
(a2-1M-1cm2) ZrC14. RPPh ZrCl4.RPOEt ZrCl,. RPOH Zr (OH)sC12* RPOEt* 8HaO Zr (OH)zClz* RPPh* 8HsO Zr (OH).$&* RPOH* 8HaO Hf( OH)&lz*RPPh*BH2O Hf( OH)zC12* RPOEt* 8HzO Hf( OH)&Xz* RPOH* 8H2O [ Zr( OH)s( RPPh)] (ClO&* 8HzO [Zr(OH)2(RPOEt)](C104)2~8HzO [ Zr( OH)z( RPOH)] (ClO4)2* 8HaO
2.45 2.23 3.10 3.53 4.40 Insoluble 4.81 3.42 4.24 20.07 14.66 13.81
TABLE 8 IR frequencies (cm-l) of the ligands and of the chloride and perchlorate zirconium and hafnium Compound
~(~,~,),~(~)~~,12~(~)(cGHs)
Zr(
(RPPh)
OH)zC12* RPPhsBH20 Hf (OH)zCla* RPPh* 8HaO ZrC14. RPPh [ Zr( OH)z( RPPh)] (ClO4)2’ 8H2O [(‘&H5)2P(O)CH2]zP(O)(OCzHs) Zr (OH)$lz* RPOEt* 8HzO Hf (OH)zCla* RPOEt* 8HaO ZrC14. RPOEt [Zr(OH)a(RPOEt)](ClO4)2*8HaO [(csH&P(O)cH,] 2P(WOW OH)&lz* RPOH. 8HaO Hf (OH)zCla* RPOH* 8HaO ZrCl4. RPOH [Zr(OH)2(RPOH)](C104)z~8Hz0
Zr(
(RPOEt)
WOW
v(P=o)
V(ClO,)
12106,11906 1160s 1175s 1170sh, 1080s 1160s
-
12456, 1175s 1170s 1185s llBOsh, 1075s llBOsh, 1150s 12486, 1175s 1160s 1160s llBOsh, 1075s 1160s
complexes of
‘(OH)
-
3450 3450
- 2900 - 2850
109Os,625m
3400
- 2900
-
3400 3400 -
- 2800 - 2850
109Os,625m
3380
- 2900
-
258Ow, 225 3450 - 2850 3400 - 2850 -
109Os,625m
3400
- 2900
the negative
perchlorate ions. The formation of multiple ion species held together by electrostatic forces is very probable. The IR data for the ligands and for the complexes examined are given in Table 8. The coordination of the ligands through oxygen from the P=O group is demonstrated by the negative u(~=~) frequency shift. Shifts of 60 - 90 cm-’ were observed. As well as a shoulder at 1160 cm- ‘, the IR spectra of the complexes ZrCl,* L
(L = RPOH, RPOEt or RPPh) show a very strong band at 1080 cm-‘,
which
110
could be assigned as a strongly coordinated P=O . . .(M) absorption band. The spectra of the oxychloride and oxyperchlorate complexes show a fairly strong wide absorption band over the range 2850 - 3450 cm-‘; this is attributed to the hydroxyl stretching vibration of water molecules and indicates the bridging of metal atoms through hydroxyl groups. The intense narrow absorption band at 800 - 1000 cm-’ associated with the presence of M=O groups is absent in all the spectra examined. The M - 0 - M vibration mode is not found in these spectra. In general, perchlorate complexes do not show any splitting of the vCclo,) bands. The non-degenerate u1 frequency which usually appears in the spectra of coordinated perchlorates in the 920 - 945 cm- ’ region is completely absent. Strong bands due to ionic perchlorate were observed at 1090 cm-’ and 625 cm-‘. In conclusion, the results obtained show that the nature of the radical bound to the central phosphorus atom and the electronegativity of the oxygen influence the extraction properties of the ligands. From non-aqueous ethanolic solutions, however, the same type of complex is built up, whichever ligand is used. From the data obtained it is difficult to determine whether the ligands act as tridentate or as bidentate agents. The IR spectra indicate that all three phosphoryl groups are involved in complex formation but the same spectra can also be obtained after polymerization.
References 1 T. Ya. Medved, Yu, M. Polikarpov, L. E. Bertina, V. G. Kossih, K. S. Yudina and M. I. Kabachnik, Uspehi Himiji, 44 (1975) 1003. 2 P. Bronzan and H. Meider-Gorican, J. Less-Common Met., 29 (1972) 407. 3 H. Meider-Gorican, J. Inorg. Nucl. Chem., 33 (1971) 1919. 4 L. Maier, Helv. Chim. Acta, 52 (1969) 827. 5 T. Ya. Medved, Yu. M. Polikarpov, S. A. Pisareva, E. I. Matrosov and M. I. Kabachnik, Izv. Akad. Nauk SSSR, Ser. Khim., (1968) 2062. 6 E. I. Matrosov, K. Zh. Kulumbetova, L. I. Arhipova, T. Ya. Medved and M. I. Kabachnik, Izv. Akad. Nauk SSSR, Ser. Khim., (1972) 193. 7 E. G. Taylor and C. A. Kraus, J. Am. Chem. Sot., 69 (1947) 1731. 8 J. Goffart and G. Duyckaerts, Anal. Chim. Acta, 36 (1965) 499. 9 J. W. O’Laughlin, D. F. Jensen, J. W. Ferguson, J. J. Richard and C. V. Banks, Anal. Chem., 40 (1968) 1931. 10 A. I. Zhukov, E. I. Kazantsey and V. N. Onosov, Zh. Neorg. Khim., 7 (1962) 915.
101
SOLVENT EXTRACTION OF ZIRCONIUM AND HAFNIUM III. EXTRACTION AND COMPLEX FORMATION WITH TRIDENTATE ORGANOPHOSPHORUS COMPOUNDS
P. BRONZAN and H. MEIDER Ruder BoskouiC Institute, Zagreb (Yugoslavia) (Received October 31, 1977)
Summary
The tridentate organophosphorus compounds bis [ (diphenylphosphinyl) methyl] phenylphosphine oxide (RPPh), bis[ (diphenylphosphinyl)methyl] phosphinic acid (RPOH) and bis[(diphenylphosphinyl)methyl] ethyl phosphinate (RPOEt) have been used for studies of zirconium and hafnium extraction from chloride, perchlorate and sulphate solutions. The formation of M(ClO&* BRPPh, M(ClO&* BRPOEt, M(ClO&. BRPOH, MC14.2RPPh, MC14. BRPOH, MC14*RPOEt, MS04( RPOH), and MS04( RPOH)z. RPOH complexes in the organic phase (M = Zr or Hf) is proposed. The extraction mechanism is discussed. The complexes Zr(OH)zCls~L~8HzO, Hf(OH)zCls*L*8HaO, ZrCII*L and [Zr(OH),(L)] (C104)s*8H20 (L = RPPh, RPOEt or RPOH) were isolated and characterized. The characteristic frequencies of the P=O, P-O-(M) and ClO, vibrations have been assigned.
1. Introduction
The extraction of zirconium and hafnium and the formation of their complexes with organophosphorus compounds have been studied by a number of authors [ 11. Our previous investigations gave evidence of the extraction of zirconium and hafnium and the formation of their complexes with some bidentate organophosphorus compounds [2, 31. There is no previous work dealing with metal complexes or solvent extraction using ligands containing three P=O groups bridged by methylene groups. This work was undertaken in order to gain information relating to the solvent extraction and complex formation properties of ligands with the general formula
102 RI C6H5\
,CH2\
,CH2\
RI = C,H,
(RPPh)
R1=OH
(RPOH)
,C6H5
RI = 0C2H5 (RPOEt) These ligands differ only in the radical RI bound to the central phosphorus atom. Depending on the nature of RI, the ligand is a phosphine oxide (RPPh), a phosphinic acid (RPOH) or a phosphinate (RPOEt). These ligands were first prepared by Maier [ 41 and by Kabachnik and his coworkers [ 51. Kabachnik and his coworkers also prepared the mono- and b&potassium salts of the ligands and proposed a mesomeric structure for the anion. Further, they proposed that the bi- potassium salt consists of two systems with delocalized bonds in different planes. The central phosphoryl group at the intersection of the planes is not equivalent to the other two. The same authors demonstrated, in perchlorate systems, hydrogen bridge formation through two oxygens. The third oxygen is not involved in hydrogen bridge formation [6] . We have also studied the effect of the radical RI on the extraction of zirconium and hafnium and on complex formation. The results obtained are given in this paper.
2. Experimental 2.1. Reagents Bis[(diphenylphosphinyl)methyl] phenylphosphine oxide (RPPh), bis[(diphenylphosphinyl)methyl] phosphinic acid (RPOH) and bis[diphenylphosphinyl)methyl] ethyl phosphinate (RPOEt) were prepared by the method used by Kabachnik et al. [5] . Radioactive 32P labelled ligands were prepared using 32PC13 (Radiochemical Centre, Amersham) as a reagent in their synthesis. Chloroform (Merck p.a.) was used without further purification as the organic solvent in the extraction experiments. Nitrobenzene for use in conductivity measurements was purified by the method of Taylor and Kraus 171. 2.2. Standard metal solutions, radioactive tracers and distribution measuremen ts The procedures used to obtain distribution data, standard metal solutions and radioactive tracers have been outlined in our earlier studies [l] .
103
2.3. Preparation of complexes The ligands, diluted in absolute ethanol, were added to an ethanolic solution of ZrCl,, ZrOCls*&HsO, ZrO(C10&*8HzO or HfOClz*8HsO. The 1igand:metal ratio was at least 1~1. The complexes were precipitated with diethylether. The precipitates were filtered and washed once with dry petroleum ether (b.p. 60 - 80 “C). The complexes precipitated were always of the same stoichiometry. 2.4. Physical measurements The molecular conductance of a millimolar solution of each complex in nitrobenzene was determined on a Tacussel conductivity bridge, type Cd 7. Potentiometric measurements were carried out on a pH meter (Radiometer PHM 64). The IR spectra of the complexes and ligands were recorded with a Perkin-Elmer 257 spectrophotometer (4000 - 625 cm-‘). Osmometric measurements were carried out with a Mechrolab osmometer, model 301 A.
3. Results and discussion 3.1. Ligand properties Because of the rather difficult preparation of the,ligands and the short half-life of the 32P isotope, only a few investigations of the distribution properties of the ligands could be carried out. The dependence of the ligand distribution on the hydrogen ion and ligand concentrations was studied. The partition of the ligands between chloroform and aqueous solutions containing 4 M H‘C104 or 0.1 M H’( [H’, Na+, ClO,] = 1 M) has been studied at various ligand concentrations. Distribution ratios obtained in these systems for the ligands RPPh and RPOEt were rather high (D > 200) and did not depend on ligand concentration. Data obtained for RPOH are given in Table 1. At concentrations higher than 10m3 M the distribution ratio increases with increasing ligand concentration. This result suggests that dimerisation occurs in this concentration range. TABLE
1
Extraction of RPOH from solutions into chloroform
[H’]
= 0.1 M, [H’,
Na+, ClO,]
= 1 M and 4 M HClOd aqueous
W’OHI (W
04 MHC10,
D[H+I =O.lM
5.0 2.5 1.25 6.25 3.12 1.56
4.54 3.14 3.03 2.19 2.09 2.33
20.30 16.85 13.75 13.72 11.74 11.42
x10-3 x1O-3 X 1O-3 X 1O-4 x 1O-4 x 1O-4
DRPOE~ and D~pph under the same conditions
are greater
than 200.
104 TABLE 2 Extraction of RPOH and RPOEt from [H’, Na+, CHaCOO-] chloroform
= 1 M aqueous solutions into
W+Ls (M)
&POH
Dw’oEt
7.1 6.5 5.9 8.9 8.5 2.4
20.4 15.1 10.8 7.7 2.4 1.4
194 108 91 80 72 63
x10-3 X lo-* x 10-5 x10-6 x 10-7 x lo-’
TABLE 3 Extraction of RPOH from [H+, Na+, ClOJ aqueous solutions into chloroform
= 1M
W+l, (W
DRPOH
2.0 1.4 6.4 1.3 3.2 1.6
9.4 13.8 19.3 28.1 26.8 22.8
x10-l x10-l x 10-2 x 1O-2
Tables 2 and 3 show the dependence of the distribution ratios of the ligands on the hydrogen ion concentration. The extraction was carried out from aqueous solutions ([Na*, H’, CH3COO-] = 1 M or [Nd, H’, ClOJ = 1 M, respectively) into chloroform. For the ligands RPOH and RPOEt, a decrease in the value of D with decreasing H’ concentration was observed for acetate/chloroform systems. The distribution of RPPh does not depend on the H’ concentration. On carrying out the extraction from perchlorate solutions with the ligand RPOH, an inverse effect was observed. For the other two ligands, D values higher than 200 were obtained in the H’ concentration range investigated. The decrease of D aron with increasing H’ concentration in perchlorate systems is a consequence of the formation of perchlorate adducts which are more soluble than the free ligand in aqueous solutions. Species formed in perchlorate systems were investigated by two-phase titration of the organic phase after equilibration of the ligand-chloroform solutions with perchloric acid. Table 4 shows the data obtained for the titration of RPPh. The results obtained indicate the formation of 1:l adducts up to 4 M HC104. At higher concentrations, the formation of 1: 2 adducts cannot be excluded. As the two-phase titration could be carried out only at ligand concentrations higher than 10m2 M, the aggregation of the perchlorate species has to be taken into
105 TABLE 4 Extraction
of HC104 into chloroform solutions (2 X lop2 M RPPh) [HC1041.,, W)
0.2 0.4 0.75 1.0 1.5 2.0 4.0 6.0 8.0
2.1 8.3 1.1 3.2 5.6 1.0 1.9 2.0 2.5
x 10-5 x 1O-5 x10-3 x 1O-3 x 1O-3 x 10-2 x 10-2 x 10-2 x 1O-2
account; this suggests that the approach used by Goffart [ 81 and Banks [ 91 is of rather limited application. For this reason the constants have not been calculated. Two-phase titration gave an indication of the species formed in the organic phase, and osmometric measurements were therefore carried out. For species isolated from perchloric acid solutions ( [HC104] > 4 M) molecular weights M higher than 1000 have been obtained, because of the aggregation of the isolated complexes. The data show monomeric RPOEt and RPPh and dimeric RPOH molecules in chloroform (MRm, talc. 554, expl. 600; Mar,,, , talc. 522, expl. 584; MaPOH, talc. 494, expl. 850). Hydrochloric and sulphuric acids are poorly extracted with the ligandchloroform solutions. The ligand RPOH is a phosphinic acid and it was of interest to determine its dissociation constant. A value of 2.64 + 0.02 for the pK was obtained by potentiometric titration from aqueous 1 M NaC104 solutions. 3.2. Zirconium and hafnium extraction The distribution ratios of zirconium and hafnium as a function of the ligand concentration are given in Fig. 1. The extraction was carried out from aqueous 4 M HC104 and 4 M HCl solutions, respectively. Some deviation from a straight line was observed for the perchloric acid/chloroform systems. This is explained by the aggregation of perchlorate adducts of the ligands. Since the ligands are not able to form adducts with HsSO4 and HCl, no deviation from straight lines for the extraction of the metals from sulphuric and hydrochloric acid solutions was observed. The high D values obtained for the extraction of the metals from perchlorate solutions are explained by the formation of rather stable complexes and the fact that perchlorate, which is a large ion with the charge smeared over the surface, is easily extracted into the organic phase. The distribution ratios as a function of ligand and HSO, concentration for the extraction of the metals from 3 M HsSO4 and [H’, Na+, ClO,,
106
3
1
1
OC
x -1
-2
-3
Fig. 1. The dependence of the extraction of Zr (0, A, 0, 0) and Hf (a, A, l, +) from 4 M HClO4 (0, 0, A, A) and 4 M HCl(0, n, 0, +) solutions on the concentration of RPPh (0, 0, D, m) or RPOEt (A, A, 0, +)_
HSOZJ = 1 M aqueous solutions, respectively, are given in Figs. 2(a) and 2(b). For the extraction of the metals with RPPh and RPOEt, low D values (D < 10b3) were obtained; these are not shown. The 1igand:metal ratios for the extraction of the metals by all three ligands and the HSO;;:metal ratio for extraction by RPOH from the systems investigated are presented in Table 5. Low metal concentrations (10m6 M) exclude polymerization. Unhydrolysed M4* species are predominant in solutions of the acidity examined [lo]. For the extraction of the metals from perchloric acid solutions the following equilibria are proposed: G f HC104 M4+ + nL-HClO
4
[ML,] ‘+ + 4[ClO4]
+
L-HC104
F=
[MLJ4*
e
[ML,] [C104] 4
(1) + nHC104
(L = RPOEt, RPPh, RPOH; n = 2 or 3 for the ligands RPPh and RPOEt, 2 for RPOH).
(2) (3) 1 or
107
I -4
'o9[RKlHI
I ,.
I -3
v
log[ Ha4-] (b)
Fig. 2. (a) The dependence of the extraction of Zr (0) and Hf (m) from 3 M HzS04 solutions on the concentration of RPOH. (b) The dependence of the extraction of Zr (0) and Hf (m) on HSOp concentration. [H’, Na+, ClO,, HSOZ] = 1 M; [RPOH] = 1 x lo-* M.
TABLE 5 Extraction of zirconium and hafnium with RPPh, RPOEt and RPOH Composition of the aqueous phase
4 M HC104 4MHCl 3 M H2SO4
HSOr/metal ratio
Ligand/metal ratio RPPh
RPOEt
RPOH
RPOH
Zr
Hf
Zr
Hf
Zr
Hf
2.8 1.8 -
2.3 2.0 -
2.5 1.2 -
2.7 1.0 -
1.3 1.6 2.6
1.5 1.5 2.2
[H+, Na+, ClO,, HSOZ] = 1 M
Zr
Hf
1.8
1.5
The shapes and slopes of the extraction curves obtained are in agreement with the results obtained for the extraction of the metals by bidentate organophosphorus compounds [ 2, 31. The conductivity measurements on the chloride species isolated (which are discussed below) indicate that the probability of extraction of dissociated species is low. On the basis of the extraction data, the formation of MC14*RPOEt, MC14-2RPPh and MC14* nRPOH (n = 1 or 2) complexes in the organic phase is proposed (M = Zr or Hf).,
108
All these results indicate that the most stable complexes are formed with the figand RPOH. With this ligand the extraction could be carried out even from aqueous 3 M HaSO4 solutions. Depending on the composition of the aqueous phase, a reaction releasing one or two HSO, ions (Fig. Z(b)) takes place, indicating that MS04(RPOH)s and MS04(RPOH)s * RPOH are formed.
Tetrachioride, oxychloride and oxyperchlorate complexes of zirconium and oxychloride complexes of hafnium have been isolated from ethanolic solutions by precipitation with diethylether. The analytical data shown in Table 6 suggest certain stoichiometries but do not reflect the real structure of the complexes. Because of the low solubihty of the complexes, we were not able to determine their molecuiar weights. Water dedication by the TABLE 6 Analytical data for zirconium and hafnium complexes with RPPh, RPOEt and RPOH Compound
ZrC14*RPPh Zr(OH)$YgRPPh*8H# ]Zr(OH)~(RPPh)](ClO4)~~8H~O Hf(OH)~C~~~~Ph*8~2~ ZrClg RPOEt Z~OH)~~i~*RPOEt*8H~# [Zr(OH)g(RPOEt)](ClC&*8H~O Hf( OH)&12*RPOEt- 8HzC ZrCl4* RPOH Zr(OH)&‘la* RPOH- 8H# ~Z~O~)~(~OH)I(C~O~)Z~~H~O Hf(OH)~C~~~RPUH- 8H20
Calculated (%)
Found (W)
M
P
CI
11.59 10.21 8.93 18.19 12.09 10.58 9.22 18.80 12.55 10.94 9.49 19.38
11.81 10.40 9.09 9.47 12.31 10.78 9.39 9.79 12.78 11.14 9.66 10.09
18.02 7.93 6.94 7.23 16.78 8.23 7.16 7.41 19.51 8.50 7.37 7.79
H20
16.13 14.09 14.67 18.70
14.02 15.17 17.26 14.94 15.63
M
P
Cl
12.07 11.10 9.82 18.75 12.95 11.39 10.05 19.52 13.35 11.30 10.28 19.92
11.32 10.54 9.14 952 12.74 11,08 9-28 9.50 12.56 Il.58 10.35 10.53
17.61 7.82 7.53 7.15 18.14 8.48 7.28 7.10 17.92 9.27 6.95 6.37
Hz
15, 14. a 15, 14. a 16. 14. a
M = Zr or Hf. aBecause only small amounts of the hafnium complexes were available, the water content of these compounds has not been determined.
Karl Fischer method and thermo~~~e~c rne~u~rnen~ indicated the presence of eight molecules of water per metal atom, Water is released over a wide temperature interval, indicating that the water molecules are bound in more than one way. The conductivity measurements given in Table 7 were carried out in nitrobenzene. The chloride and oxychloride complexes of the metals are nonelectrolytes. Values of 14 - 20 for 10m3 M solutions of the perchlorate complexes were obtained. As the IR spectra show no coordination of the perchlorate ion, the low activity of the perchlorate ion in nitrobenzene solution can be explained by the formation of highly charged polymeric metal-hydroxy-ligand complexes which exert an attractive force on
109
TABLE 7 Conductivity
data for the chloride
and perchlorate
complexes
of zirconium
Compound
and
hafnium
&I (10-3M)
(a2-1M-1cm2) ZrC14. RPPh ZrCl4.RPOEt ZrCl,. RPOH Zr (OH)sC12* RPOEt* 8HaO Zr (OH)zClz* RPPh* 8HsO Zr (OH).$&* RPOH* 8HaO Hf( OH)&lz*RPPh*BH2O Hf( OH)zC12* RPOEt* 8HzO Hf( OH)&Xz* RPOH* 8H2O [ Zr( OH)s( RPPh)] (ClO&* 8HzO [Zr(OH)2(RPOEt)](C104)2~8HzO [ Zr( OH)z( RPOH)] (ClO4)2* 8HaO
2.45 2.23 3.10 3.53 4.40 Insoluble 4.81 3.42 4.24 20.07 14.66 13.81
TABLE 8 IR frequencies (cm-l) of the ligands and of the chloride and perchlorate zirconium and hafnium Compound
~(~,~,),~(~)~~,12~(~)(cGHs)
Zr(
(RPPh)
OH)zC12* RPPhsBH20 Hf (OH)zCla* RPPh* 8HaO ZrC14. RPPh [ Zr( OH)z( RPPh)] (ClO4)2’ 8H2O [(‘&H5)2P(O)CH2]zP(O)(OCzHs) Zr (OH)$lz* RPOEt* 8HzO Hf (OH)zCla* RPOEt* 8HaO ZrC14. RPOEt [Zr(OH)a(RPOEt)](ClO4)2*8HaO [(csH&P(O)cH,] 2P(WOW OH)&lz* RPOH. 8HaO Hf (OH)zCla* RPOH* 8HaO ZrCl4. RPOH [Zr(OH)2(RPOH)](C104)z~8Hz0
Zr(
(RPOEt)
WOW
v(P=o)
V(ClO,)
12106,11906 1160s 1175s 1170sh, 1080s 1160s
-
12456, 1175s 1170s 1185s llBOsh, 1075s llBOsh, 1150s 12486, 1175s 1160s 1160s llBOsh, 1075s 1160s
complexes of
‘(OH)
-
3450 3450
- 2900 - 2850
109Os,625m
3400
- 2900
-
3400 3400 -
- 2800 - 2850
109Os,625m
3380
- 2900
-
258Ow, 225 3450 - 2850 3400 - 2850 -
109Os,625m
3400
- 2900
the negative
perchlorate ions. The formation of multiple ion species held together by electrostatic forces is very probable. The IR data for the ligands and for the complexes examined are given in Table 8. The coordination of the ligands through oxygen from the P=O group is demonstrated by the negative u(~=~) frequency shift. Shifts of 60 - 90 cm-’ were observed. As well as a shoulder at 1160 cm- ‘, the IR spectra of the complexes ZrCl,* L
(L = RPOH, RPOEt or RPPh) show a very strong band at 1080 cm-‘,
which
110
could be assigned as a strongly coordinated P=O . . .(M) absorption band. The spectra of the oxychloride and oxyperchlorate complexes show a fairly strong wide absorption band over the range 2850 - 3450 cm-‘; this is attributed to the hydroxyl stretching vibration of water molecules and indicates the bridging of metal atoms through hydroxyl groups. The intense narrow absorption band at 800 - 1000 cm-’ associated with the presence of M=O groups is absent in all the spectra examined. The M - 0 - M vibration mode is not found in these spectra. In general, perchlorate complexes do not show any splitting of the vCclo,) bands. The non-degenerate u1 frequency which usually appears in the spectra of coordinated perchlorates in the 920 - 945 cm- ’ region is completely absent. Strong bands due to ionic perchlorate were observed at 1090 cm-’ and 625 cm-‘. In conclusion, the results obtained show that the nature of the radical bound to the central phosphorus atom and the electronegativity of the oxygen influence the extraction properties of the ligands. From non-aqueous ethanolic solutions, however, the same type of complex is built up, whichever ligand is used. From the data obtained it is difficult to determine whether the ligands act as tridentate or as bidentate agents. The IR spectra indicate that all three phosphoryl groups are involved in complex formation but the same spectra can also be obtained after polymerization.
References 1 T. Ya. Medved, Yu, M. Polikarpov, L. E. Bertina, V. G. Kossih, K. S. Yudina and M. I. Kabachnik, Uspehi Himiji, 44 (1975) 1003. 2 P. Bronzan and H. Meider-Gorican, J. Less-Common Met., 29 (1972) 407. 3 H. Meider-Gorican, J. Inorg. Nucl. Chem., 33 (1971) 1919. 4 L. Maier, Helv. Chim. Acta, 52 (1969) 827. 5 T. Ya. Medved, Yu. M. Polikarpov, S. A. Pisareva, E. I. Matrosov and M. I. Kabachnik, Izv. Akad. Nauk SSSR, Ser. Khim., (1968) 2062. 6 E. I. Matrosov, K. Zh. Kulumbetova, L. I. Arhipova, T. Ya. Medved and M. I. Kabachnik, Izv. Akad. Nauk SSSR, Ser. Khim., (1972) 193. 7 E. G. Taylor and C. A. Kraus, J. Am. Chem. Sot., 69 (1947) 1731. 8 J. Goffart and G. Duyckaerts, Anal. Chim. Acta, 36 (1965) 499. 9 J. W. O’Laughlin, D. F. Jensen, J. W. Ferguson, J. J. Richard and C. V. Banks, Anal. Chem., 40 (1968) 1931. 10 A. I. Zhukov, E. I. Kazantsey and V. N. Onosov, Zh. Neorg. Khim., 7 (1962) 915.