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On the α-dioximine complexes of transition metals—LX
! more nu¢/. ('hem Vol. 43, pp. 111-113 Pergamo~ Press [Id. 19gl Printed in (;real Britain
ON THE a-DIOXIMINE COMPLEXES OF TRANSITION METALS--LX T H E S T A B I L I T Y O F T H E Fe(II), Co(II) and Ni(II) C O M P L E X E S OF 1,2-CYCLOHEPTANE DIONE DIOXIME AND 1,2-CYCLOOCTANE D I O N E D I O X I M E IN D I O X A N E - W A T E R
MIXTURES
J. HOR,~K, Z. FINTA and Cs. VARHELYI Faculty of Chem. Technology, "Babes-Bolyai University"--Cluj-Napoca, Str. Arany J~inos No. I I, Romania
tReceived 23 August 1979: receivedfor publication 20 February 1980) Abstract--The acid dissociation constants of the 1,2-cycloheptane dione dioxime ~Heptoxime) and 1,2-cyclooctane dione dioxime (Octoxime), as well as the stability constants of the Fe(II), Co(II) and Ni(II) complexes of these ligands were determined by potentiometric titrations, in 75% vol. dioxane--25% vol. water mixtures. On the basis of a relation given in the literature and tested in the case of the studied Fe(lI) and CoOl) complexes, the st~tbility constants of the slightly soluble Ni(ll) complexes were also extrapolated for aqueous solutions.
Potentiometric titrations. In order to obtain the first acid dissociation constants K, of the studied vic-dioximes, samples of 25 ml containing dioxime, perchloric acid and NaCIO4 in 75% vol. dioxane-25% vol. water mixture were titrated with NaOH 9.66 x 10-2 M at 20 _+0. I°C in purified and water saturated methane atmosphere. Increments of dioxane were added to the solution for keeping the composition of the solvent constant. The replacement of the second hydrogen ion from the dioxime was avoided by adding only at most 0.2 mole NaOH per mole of dioxime. The variation of the ionic strength of 0.1 M during the titrations was not significant. The concentration of the hydrogen ions was measured with a RADELKIS-OP 205 precision pH-meter, using an OP 717-1/A type combined electrode. The rapid mixing of the solutions was assured by means of a magnetic stirrer, which was stopped during the actual pH-measurements. In order to cover the whole pH-range in which complex formation occurs, the titrations were carried out beginning from pH ~ 2. The values of K,, were calculated from the titration data by using the relation:
INTRODUCTION The formation, structure and stability of some dimethylglyoxime complexes with important analytical applications have been thoroughly investigated. The analogous complexes of other vic-dioximes, including alkyl- and dialkyl-glyoximes, benzyldioxime and 5-7 membered cycloalkyl dioximes, have also been studied in various experimental conditions and by different methods[I-8]. However, data concerning the formation and stability of complexes with cycloalkyl dioximes containing more than seven membered rings have not been reported. In a previous paper[9] the stability constants of the FedI) and Co(II) complexes with 1,2-cycloheptane dione dioxime (Heptoxime, Heptox × H~_: C7Ht2N202) and 1,2cyclooctane dione dioxime (Octoxime, Octox. H2: C,H~4N2Oz) were determined in aqueous solutions by potentiometric titrations. In these conditions, however, the analogous Ni(Ii)-complexes cannot be studied due to their very low solubility in water. On that account, in the present paper the stability of all these complexes was investigated in 75% vol. dioxane-25% vol. water mixtures and the stability constants of the Ni(II) complexes were extrapolated for aqueous solutions.
K,,
-
[tt+](C N~'OH -- CHCIO4 - [H+] - K J I H ']) - -
Cl~io, .~ (CN,oH- CHclo, + [H +] - K~./[H'I)
EXPERIMENTAL
Reagents. The 1,2-cycloheptane dione dioxime and the i,2cyclooctane dione dioxime were obtained by the oxidation of cycloheptanone and cyclooctanone with selenium dioxide in boiling absolute ethanol, followed by the oximation of the 1,2diones with an excess of NH,OH, HCI and KOH (molar ratio: I:l) in aqueous solution. The crude products were recrystallized from hot water[13, 14]. Their purity was determined gravimetrically as [Ni(Diox × Hh] from acetate buffer solution. Fe(ll), Co(II) and Ni(lI) perchlorates were prepared from ',tnalytical grade carbonates and perchloric acid. The NaOH solution was obtained from NaOH p.a. and distilled water free of CO,. NaCIO4 p.a. w~s used to establish the constant ionic strength of 0.1 M. Dioxane was purified by Vogel's method[15] and passed through an activated alumina column immediately before use. 111
where K~ = 4.63 ~ 10 t8 extrapolated from literature data[16]. The stability constants of the studied complexes were determined by titration with NaOH 9.66.10 2M of samples prepared as described above, but containing also the corresponding transition metal perchlorate (metal:dioxime=l:2.5). The initial concentrations in the samples were: CM2~ -4.0× 10 4M, CDiox H2 = 1.0.10 ~'M, CHClO4= 1.04.10-' M. In the above described experimental conditions, the hydrolysis of the metal ions, as well as the oxidation of the free or coordinated ones. was neglectible. The ti and Diox.H values were calculated from the potentiometric titration data by means of the relations: K C [Diox.n ] = [ ~ ( .c,o,+CD,,,x H,-CN,o.-[H+] ~ K JIM÷l) and
fi=CDi,,~HZ (I-[H+]/Ka)[H +] CM 2.
RESULTS
AND DISCUSSION
In dioxane-water solutions containing various transition metal ions (M 2+) and vic-dioximes (Diox.H2) the
J. HORAKet al.
112 following equilibria have been taken into account:
means of the least square method. For each complex, l0 experimental values were taken between ti ~0.3 and ri ~ 1.75. The corresponding fll and /32 values are listed in Table I. The stability constants obtained for the studied complexes in dioxane-water mixtures allow us to approximate the stability of the Ni(II) complexes in water in the same conditions, on the basis of the relation
Ka
Diox.H2 ~ Diox.H- + H ÷
(l)
Ki
(2)
M2+ + Diox'H- ~ [M(Diox.H)] + K2
[M(Diox. H)]+ + Diox.H- ~ [M(Diox.Hh].
(3)
log fl, - log fl,(w) = pKa - pKa(w)
The values of the first acid dissociation constant K~ calculated from the potentiometric titration data, are (4.01 -+0.17)× l0 -14 for Heptoxime and (5.21 _+0.24)× 10-14 for Octoxime. These values show the Octoxime to be a stronger acid as compared to Heptoxime, as it was also found in aqueous solutions[10]. The Ka value of Heptoxime agrees well with that of 4.68 × l0 -14 obtained at 25°C in the same solution and ionic strength 1. The stability constants were derived from the ti and Diox.H- data by using the complex formation function[l 1]:
given by Irving and Rossotti[12] for (ML) type complexes. (The symbols (w) indicate the corresponding values of K, and Ka in water). Although the above relationship is valid only for l: 1 complexes, approximations for 1/21ogfl2(w) were also attempted by using the experimentally obtained log/32. First the validity of the relation (6) was tested with the aid of the /3,(w) and [32(w) values of the Fe(II) and Co(II) complexes reported in our previous paper[10] also included in the Table 1. The mean values of log fll- log [3,(w) (2.81 for Heptoxime and 2.91 for Octoxime) are quite close to the corresponding pKa-pKa(w) terms (2.75 and 2.84, respectively), but the mean values calculated for the 1/2 log f12- 1/2 log fl2(w) are too low (2.36 and 2.45), as compared to the pKa-pK~(w) differences. On the other hand, the value of the ratio fll/fl2 of the Ni(II) complexes differs strongly from that of the analogous Fe(II) and Co(II) compounds. In these conditions, the conclusion is, that a good approximation on the basis of eqn (6) can be made only for/31, but not also for the overall stability constants of the Ni(II) complexes. Therefore, the extrapolated /32(w) values given in Table 1, are somewhat uncertain. As seen from the stability data presented in Table 1, the order of the increasing stability of both the Heptoxime and Octoxime complexes is Ni(II)
N
E ifl,[L-]' -
N
I
(4)
+ ~/3,[L-]' !
explicited for N = 2 and transformed into the form ti
(1 ti)Diox.H-
2-ti . _ =/32 7~_- [Dlox'H ]+/3,
(5)
Where/31 = K , and/32 = K1K2. The linearity of the curves obtained by plotting 2- n ti J - ~ [Diox'H-] vs (1 - ti)[Diox.H-] is quite satisfactory, as it is illustrated on the Fig. I. In these conditions fll and/32 were calculated as the slope and intercept of the obtained straight lines by
m T
_o
I
x _
o/
;=, ,~
,,c
2
2-fi
[Diox H - ] x IO13
I
~
-20
C
(6)
20
Fig. 1. Determination of stability constants of the [Fe(Diox.H)2] complexes: (l)-Diox.H2=Heptoxime, (2)Diox.H2= Octoxime.
113
The oMioximine complexes of transitiom metals--LX Table 1. Stability constants of Fe(II), CoOl) and Ni(II) complexes of Heptoxime and Octoxime in water and in 75% vol. dioxane-25% vol. water mixtures, at 20°C and #=0.1M Dioxane(75% vol)-water (25% vol)
Water+
Complex
/3~ x 10 ,2
f12 × 10-24
/3, × 10 io
/32 x 10 [9
[Fe(Heptox.H)2] [Co(Heptox.H)2] [Ni(Heptox.H)2] [Fe(Octox.H)2] [Co(Octox.H)2] [Ni(Octrox.H)2]
16.8-+0.8 10.7-+0.3 3.37-+0.05 12.6-+0.8 6.25-+0.45 2.07-+0.05
4.49-+0.33 1.71 _+0.10 6.33-+0.38 351-+0.38 1.08-+0.10 4.27_+0.25
2.90-+0.15 1.51 -+0.10 (0.603) 1.62-+0.18 0.742_+0.08 (0.380)
I0.2+0.3 2.70-+0.15 (2.00) 4.97-+0.30 1.22-+0.10 (1.45)
*Data for Fe(II) and Co(II) complexes taken from [9]. compared to the Octoxime, in agreement with the Ko values of these ligands.
REFERENCES
I. C. V. Banks and S. Anderson, lnorg. Chem. 2, 112 (1%3). 2. V. M. Peshkova and V. M. Bochkova, Nauchn. Dokl. Vysshei Shkoly, Khim. Khim. Technol. 1958, 62. 3. V. M. Savostina, E. K. Astakhova and V. M. Peshkova, Zhur. Neorgan. Khim. 9, 80 (1964). 4. V. M. Bochkova and V. M. Peshkova, Zhur. Neorgan. Khim. 3, 1131 (1958). 5. K. Burger, Coordination Chemistry: Experimental Methods, p. 350. Akadgmiai Kiad6, Budapest (1973). 6. E. K. Astakhova, V. M. Savostina and V. M. Peshkova, Zhur Neorgan. Khim. 9, 817 (1%4).
JINC Vol 4 t No. I--H
7. K. Burger arid I. Ruff, Acta Chim. Acad. Sci. Hung. 49, I (1%6). 8. K. Burger and E. Papp-Moln~.r, Magyar Kdm. Folydirat 73. 77 (1%7). 9. C. Macarovici, J. Hofftk and Cs. Vfirhelyi, Rev. Roumaine Chim. 6,000 (1980). In press. I0. J. Zsak6, J. t-lofftk, Z. Fin+a, Cs. V~.rhelyi and J. Mitrache, Mikrochim. Acta I, 405 (1979). 11. J. Bjerrum, Metal Ammine Formation in Aqueous 5alution, p. 15. Hall, Copenhagen (1941). 12. H. Irving and H. Rossotti, Acta Chem. Scand. 10, 72 (1956). 13. E. Miiller and M. Bauer, Liebigs Ann. Chem. 654, 105 (1%2). 14. A. Harr, R. C. Voter and C. V. Banks, J. Org. Chem. 14, 8362 (1949). 15. A. I. Vogel, A Text-book of Practical Organic Chemistry, 3rd Edn., p. 177. Longmans, Green & Co., London (1956). t6. G. Baughma~ and E. Griinwald, J. Am. Chem. Soc. 80, 3844 (1958).
ON THE a-DIOXIMINE COMPLEXES OF TRANSITION METALS--LX T H E S T A B I L I T Y O F T H E Fe(II), Co(II) and Ni(II) C O M P L E X E S OF 1,2-CYCLOHEPTANE DIONE DIOXIME AND 1,2-CYCLOOCTANE D I O N E D I O X I M E IN D I O X A N E - W A T E R
MIXTURES
J. HOR,~K, Z. FINTA and Cs. VARHELYI Faculty of Chem. Technology, "Babes-Bolyai University"--Cluj-Napoca, Str. Arany J~inos No. I I, Romania
tReceived 23 August 1979: receivedfor publication 20 February 1980) Abstract--The acid dissociation constants of the 1,2-cycloheptane dione dioxime ~Heptoxime) and 1,2-cyclooctane dione dioxime (Octoxime), as well as the stability constants of the Fe(II), Co(II) and Ni(II) complexes of these ligands were determined by potentiometric titrations, in 75% vol. dioxane--25% vol. water mixtures. On the basis of a relation given in the literature and tested in the case of the studied Fe(lI) and CoOl) complexes, the st~tbility constants of the slightly soluble Ni(ll) complexes were also extrapolated for aqueous solutions.
Potentiometric titrations. In order to obtain the first acid dissociation constants K, of the studied vic-dioximes, samples of 25 ml containing dioxime, perchloric acid and NaCIO4 in 75% vol. dioxane-25% vol. water mixture were titrated with NaOH 9.66 x 10-2 M at 20 _+0. I°C in purified and water saturated methane atmosphere. Increments of dioxane were added to the solution for keeping the composition of the solvent constant. The replacement of the second hydrogen ion from the dioxime was avoided by adding only at most 0.2 mole NaOH per mole of dioxime. The variation of the ionic strength of 0.1 M during the titrations was not significant. The concentration of the hydrogen ions was measured with a RADELKIS-OP 205 precision pH-meter, using an OP 717-1/A type combined electrode. The rapid mixing of the solutions was assured by means of a magnetic stirrer, which was stopped during the actual pH-measurements. In order to cover the whole pH-range in which complex formation occurs, the titrations were carried out beginning from pH ~ 2. The values of K,, were calculated from the titration data by using the relation:
INTRODUCTION The formation, structure and stability of some dimethylglyoxime complexes with important analytical applications have been thoroughly investigated. The analogous complexes of other vic-dioximes, including alkyl- and dialkyl-glyoximes, benzyldioxime and 5-7 membered cycloalkyl dioximes, have also been studied in various experimental conditions and by different methods[I-8]. However, data concerning the formation and stability of complexes with cycloalkyl dioximes containing more than seven membered rings have not been reported. In a previous paper[9] the stability constants of the FedI) and Co(II) complexes with 1,2-cycloheptane dione dioxime (Heptoxime, Heptox × H~_: C7Ht2N202) and 1,2cyclooctane dione dioxime (Octoxime, Octox. H2: C,H~4N2Oz) were determined in aqueous solutions by potentiometric titrations. In these conditions, however, the analogous Ni(Ii)-complexes cannot be studied due to their very low solubility in water. On that account, in the present paper the stability of all these complexes was investigated in 75% vol. dioxane-25% vol. water mixtures and the stability constants of the Ni(II) complexes were extrapolated for aqueous solutions.
K,,
-
[tt+](C N~'OH -- CHCIO4 - [H+] - K J I H ']) - -
Cl~io, .~ (CN,oH- CHclo, + [H +] - K~./[H'I)
EXPERIMENTAL
Reagents. The 1,2-cycloheptane dione dioxime and the i,2cyclooctane dione dioxime were obtained by the oxidation of cycloheptanone and cyclooctanone with selenium dioxide in boiling absolute ethanol, followed by the oximation of the 1,2diones with an excess of NH,OH, HCI and KOH (molar ratio: I:l) in aqueous solution. The crude products were recrystallized from hot water[13, 14]. Their purity was determined gravimetrically as [Ni(Diox × Hh] from acetate buffer solution. Fe(ll), Co(II) and Ni(lI) perchlorates were prepared from ',tnalytical grade carbonates and perchloric acid. The NaOH solution was obtained from NaOH p.a. and distilled water free of CO,. NaCIO4 p.a. w~s used to establish the constant ionic strength of 0.1 M. Dioxane was purified by Vogel's method[15] and passed through an activated alumina column immediately before use. 111
where K~ = 4.63 ~ 10 t8 extrapolated from literature data[16]. The stability constants of the studied complexes were determined by titration with NaOH 9.66.10 2M of samples prepared as described above, but containing also the corresponding transition metal perchlorate (metal:dioxime=l:2.5). The initial concentrations in the samples were: CM2~ -4.0× 10 4M, CDiox H2 = 1.0.10 ~'M, CHClO4= 1.04.10-' M. In the above described experimental conditions, the hydrolysis of the metal ions, as well as the oxidation of the free or coordinated ones. was neglectible. The ti and Diox.H values were calculated from the potentiometric titration data by means of the relations: K C [Diox.n ] = [ ~ ( .c,o,+CD,,,x H,-CN,o.-[H+] ~ K JIM÷l) and
fi=CDi,,~HZ (I-[H+]/Ka)[H +] CM 2.
RESULTS
AND DISCUSSION
In dioxane-water solutions containing various transition metal ions (M 2+) and vic-dioximes (Diox.H2) the
J. HORAKet al.
112 following equilibria have been taken into account:
means of the least square method. For each complex, l0 experimental values were taken between ti ~0.3 and ri ~ 1.75. The corresponding fll and /32 values are listed in Table I. The stability constants obtained for the studied complexes in dioxane-water mixtures allow us to approximate the stability of the Ni(II) complexes in water in the same conditions, on the basis of the relation
Ka
Diox.H2 ~ Diox.H- + H ÷
(l)
Ki
(2)
M2+ + Diox'H- ~ [M(Diox.H)] + K2
[M(Diox. H)]+ + Diox.H- ~ [M(Diox.Hh].
(3)
log fl, - log fl,(w) = pKa - pKa(w)
The values of the first acid dissociation constant K~ calculated from the potentiometric titration data, are (4.01 -+0.17)× l0 -14 for Heptoxime and (5.21 _+0.24)× 10-14 for Octoxime. These values show the Octoxime to be a stronger acid as compared to Heptoxime, as it was also found in aqueous solutions[10]. The Ka value of Heptoxime agrees well with that of 4.68 × l0 -14 obtained at 25°C in the same solution and ionic strength 1. The stability constants were derived from the ti and Diox.H- data by using the complex formation function[l 1]:
given by Irving and Rossotti[12] for (ML) type complexes. (The symbols (w) indicate the corresponding values of K, and Ka in water). Although the above relationship is valid only for l: 1 complexes, approximations for 1/21ogfl2(w) were also attempted by using the experimentally obtained log/32. First the validity of the relation (6) was tested with the aid of the /3,(w) and [32(w) values of the Fe(II) and Co(II) complexes reported in our previous paper[10] also included in the Table 1. The mean values of log fll- log [3,(w) (2.81 for Heptoxime and 2.91 for Octoxime) are quite close to the corresponding pKa-pKa(w) terms (2.75 and 2.84, respectively), but the mean values calculated for the 1/2 log f12- 1/2 log fl2(w) are too low (2.36 and 2.45), as compared to the pKa-pK~(w) differences. On the other hand, the value of the ratio fll/fl2 of the Ni(II) complexes differs strongly from that of the analogous Fe(II) and Co(II) compounds. In these conditions, the conclusion is, that a good approximation on the basis of eqn (6) can be made only for/31, but not also for the overall stability constants of the Ni(II) complexes. Therefore, the extrapolated /32(w) values given in Table 1, are somewhat uncertain. As seen from the stability data presented in Table 1, the order of the increasing stability of both the Heptoxime and Octoxime complexes is Ni(II)
N
E ifl,[L-]' -
N
I
(4)
+ ~/3,[L-]' !
explicited for N = 2 and transformed into the form ti
(1 ti)Diox.H-
2-ti . _ =/32 7~_- [Dlox'H ]+/3,
(5)
Where/31 = K , and/32 = K1K2. The linearity of the curves obtained by plotting 2- n ti J - ~ [Diox'H-] vs (1 - ti)[Diox.H-] is quite satisfactory, as it is illustrated on the Fig. I. In these conditions fll and/32 were calculated as the slope and intercept of the obtained straight lines by
m T
_o
I
x _
o/
;=, ,~
,,c
2
2-fi
[Diox H - ] x IO13
I
~
-20
C
(6)
20
Fig. 1. Determination of stability constants of the [Fe(Diox.H)2] complexes: (l)-Diox.H2=Heptoxime, (2)Diox.H2= Octoxime.
113
The oMioximine complexes of transitiom metals--LX Table 1. Stability constants of Fe(II), CoOl) and Ni(II) complexes of Heptoxime and Octoxime in water and in 75% vol. dioxane-25% vol. water mixtures, at 20°C and #=0.1M Dioxane(75% vol)-water (25% vol)
Water+
Complex
/3~ x 10 ,2
f12 × 10-24
/3, × 10 io
/32 x 10 [9
[Fe(Heptox.H)2] [Co(Heptox.H)2] [Ni(Heptox.H)2] [Fe(Octox.H)2] [Co(Octox.H)2] [Ni(Octrox.H)2]
16.8-+0.8 10.7-+0.3 3.37-+0.05 12.6-+0.8 6.25-+0.45 2.07-+0.05
4.49-+0.33 1.71 _+0.10 6.33-+0.38 351-+0.38 1.08-+0.10 4.27_+0.25
2.90-+0.15 1.51 -+0.10 (0.603) 1.62-+0.18 0.742_+0.08 (0.380)
I0.2+0.3 2.70-+0.15 (2.00) 4.97-+0.30 1.22-+0.10 (1.45)
*Data for Fe(II) and Co(II) complexes taken from [9]. compared to the Octoxime, in agreement with the Ko values of these ligands.
REFERENCES
I. C. V. Banks and S. Anderson, lnorg. Chem. 2, 112 (1%3). 2. V. M. Peshkova and V. M. Bochkova, Nauchn. Dokl. Vysshei Shkoly, Khim. Khim. Technol. 1958, 62. 3. V. M. Savostina, E. K. Astakhova and V. M. Peshkova, Zhur. Neorgan. Khim. 9, 80 (1964). 4. V. M. Bochkova and V. M. Peshkova, Zhur. Neorgan. Khim. 3, 1131 (1958). 5. K. Burger, Coordination Chemistry: Experimental Methods, p. 350. Akadgmiai Kiad6, Budapest (1973). 6. E. K. Astakhova, V. M. Savostina and V. M. Peshkova, Zhur Neorgan. Khim. 9, 817 (1%4).
JINC Vol 4 t No. I--H
7. K. Burger arid I. Ruff, Acta Chim. Acad. Sci. Hung. 49, I (1%6). 8. K. Burger and E. Papp-Moln~.r, Magyar Kdm. Folydirat 73. 77 (1%7). 9. C. Macarovici, J. Hofftk and Cs. Vfirhelyi, Rev. Roumaine Chim. 6,000 (1980). In press. I0. J. Zsak6, J. t-lofftk, Z. Fin+a, Cs. V~.rhelyi and J. Mitrache, Mikrochim. Acta I, 405 (1979). 11. J. Bjerrum, Metal Ammine Formation in Aqueous 5alution, p. 15. Hall, Copenhagen (1941). 12. H. Irving and H. Rossotti, Acta Chem. Scand. 10, 72 (1956). 13. E. Miiller and M. Bauer, Liebigs Ann. Chem. 654, 105 (1%2). 14. A. Harr, R. C. Voter and C. V. Banks, J. Org. Chem. 14, 8362 (1949). 15. A. I. Vogel, A Text-book of Practical Organic Chemistry, 3rd Edn., p. 177. Longmans, Green & Co., London (1956). t6. G. Baughma~ and E. Griinwald, J. Am. Chem. Soc. 80, 3844 (1958).