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The study of enantioselectivity in copper complexes with some 1,3-dicarbonyl ligands by circular dichroism spectroscopy
P~yked~n Vol. 2, No. I, pp. 37-41, 1983 Printed inGreat Briiain.
THE STUDY OF ENANTIOSELECTIVITY IN COPPER COMPLEXES WITH SOME 1,3-DICARBONYL LIGANDS BY CIRCULAR DICHROIS~ SPECTROSCOPY A. A. KURGANOV,* L. YA. ZHUCHKOVA and V. A. DAVANKOV
NesmeyanovInstitute of Organo-ElementCompounds,U.S.S.R. Academyof Sciences, 117813Moscow, U.S.S.R. (Receioed 10 June 1982) Abstract-The circular diehroism spectra of copper(H) complexes with hydroxymethylene camphor, hydroxymethylene menthone, and trifluoroacetyl camphor as well as of mixed-&and complexes with acetylacetone have been studied in different solvents at different temperat~es. The changes observed in the spectra are attributed to a strong coordination of the soivent molecules in axial positions of square-planar complexes. It has been shown that the contributions of two ligands to the net spectrum of circular dichroism are additive and that the absorption spectraof the complexes do not depend on the optical configuration of the ligands. The conclusion has been drawn that no noticeableinter-@andinteractionsexist in the complexesand no en~tioselective effects are exhibited.
INTRODUCTION Enantioselective effects in labile coordination compounds attract attention of many researchers due to an important role which they play in a number of biological systems’ and in connection with the development of the method of lied-exchange c~omato~aphic resolution of racemic compounds.2’3The most part of investigations in this field involves amino acid ligands’~* whereas information on ligands of other types is much more limited. In previous papers we have considered the reasons for enantioselectivity in coppe~1~ complexes with N - alkyl - a: - amino acids4 and 1,2-diamines.5 In this report we present the results of studying enantiosele~tivity in copper(H) complexes with 3-hydroxymethylene camphor (HMC), 3-trifluoroacetyl camphor (TFC), and 2-hydroxymethyl menthone (HMM).
Complexes of ~ansition metals with 1,3-dic~bonyl ligands were the object of numerous studies and are covered in several reviews.6.’ These papers, however, give only min~um attention to &optical properties of Cu(II) complexes with HMC, TFC and HMM which, in our opinion, deserve thorough investigation. RESULTSANDDISCUSSION I. CD spec~rff of co~p~e~es
As is seen from Fig. 1, the spectra of circular dichroism (CD) of copper complexes with HMC, TFC, and HMM are characterized by l-2 bands in the region of d-d ~ansitions of CufII) atom and by a number of bands in a shorter wavelength region. Such a shape of the CD *Author to whom correspondence should be addressed. ?The data obtained mainly, for different ~~ogen~on~i~~ axial ligands.
spectrum, as is now welf known, is related to the formation of a pseudo~omatic chelate ring in the complexes of l,$diketones and is caused by considerable delocalization of n-electron system of ligands. We considered it interesting to study the effect of solvent and temperature on the shape of the CD spectrum, In aprotic non-polar solvents (hexane, toluene) the bands at - 560 and - 700 nm have a maximum intensity. The intensity decreases in solvents capable of coordination in axial positions of square-planar complexes ~me~anol, acetone, dioxane, a~eto~~le). In the UV region the solvent effects weakly the shape of the CD spectra of Cu(HMQ and Cu(TFQ whereas in the case of Cu~HM~* this effect is strongly pronounced and the transition from acetonitrile to hexane results in an almost complete disappearance of the band at - 340 nm and in a sign change of the band at -4OOnm. It should be, however, noted that correlation with the type of the solvent for Cu(HMM)* is less pronounced than for Cu(HMQ and Cu(TF&. Temperature practically does not affect the shape of the CD spectra: the most sensitive to a temperature change proves to be the band at -~nm whose intensity (in the case of Cu(HMC)*) decreases by about 20% with a temperature rise from 25 to 55” (in methanol). The intensity of other bands changes by only 5-R%. The fact that there is no correlation between the dependence of the CD spectra on the type of the solvent and temperature in a readily coordinating solvent may be explained if the eq~ibrium between a square-plans complex and its adduct with the solvent is almost completely shifted towards adduct and does not depend on temperature. This conclusion is supported by data in the literaturep” showing that the formation constant of such adducts with a composition 1: It is - 10” for Cu(HMQ and Cu(HMM), and -1031/mol for Cu(TF&. Since the solvent concentration is high, these values correspond to almost qu~ti~tive formation of the adduct in solution. Thus, the changes observed in CD spectra of Cu(HMQ2 and Cu(TFC&, when passing from non-coordinating solvents to coordinating ones, are probably due to the fo~ation of adducts with the solvents and refer, mainly, to the region of d-d transitions. As regards 37
A. A. KURGANOV et al.
,E
4
Al io.4
fO.3
+0.2
.
+4.
u
+2
.o.-
0
-2
.
-0.
-4,c 1’
-6.c
-0.
-0.3
I-
Fig. l(a).
c
P
i
/
_
c
-6.C
,
Fig. l(b).
The studyof euautioselectivity in coppercomplexes
39
Pi
+lO +8
+6
,-
Fig. l(c). Fii. 1. CD spectraof the complexesCu[(lS)-HMC]2 (A), Cu[(lS)-TFC]2 (B), Cu[(lR)-HMMJ2 (C) in Mereot solvents:1, hexane;2, methanol;3, dioxane;4, acetooe;5, tolueoe;6, acetonibile.
Cu(HMl& whose ligands are conformationally more labile than the ligands of camphor derivatives, the formation of adducts, is most likely accompanied by conformational changes and the effect of the solvent manifests itself in the whole region of wave lengths from 200 to 700 nm. 2. Enantiosefectiuity in complexes CU(HMC)~,CU(TFC)~ and Cu(HMM)2 Enantioselectivity in complexes of the ML type arises when there is a mutual effect between two ligands entering into the complex. This mutual effect appears in different forms. Thus, for instance, in the case of complexes of N - alkyl - a - amino acids” it manifests itself in the ditIerent ability of the complexes containing two ligands of identical or opposite cot&nation, to the addition of a solvent molecule in the axial position of Cu2+. In the CD spectra the mutual effect of the ligands appears as a deviation from additivity of the contributions of both ligands into the net CD spectrum. To detect the deviations from the additivity of contributions, we have studied CD spectra of mixed complexes in which HMC, HMM, or TFC was one of the ligands and the acetylacetone (AA) molecule was the second ligand. Acetylacetone is one of the smallest liiands of the 1,3-dicarbonyl type and one may expect that no noticeable steric interactions with the second lid will take place. Only in the case of CU(HMC)~ small deviations in the region -620nm were detected
-0.2-0.4.
IQ. 2. CD spectraof mixed complexesCuj[(lS)-HMCl(AA)}, 1,3-initialcomplexes,2-mixedcomplex.Chloroform as a solvent. (Fig. 2). The formation constant of mixed complex is also close to 4 which means that distribution of the ligands in the system Cu(HMCkCu(AA)&$HMC)(AA) is almost statistical in nature. The absorption spectra of C~IK~R)-(HMC)]~,Cu[(lS& (HMCIIZ and CuI(lR,lS)-(HMC)12 as well as of Cu[(lR)TFC$, Cu[(lS)-TFC12 and Cu[(lR,lS)-(TFC)], are completely identical; the differences between them are within the limits of accuracy of the measurements. All the results obtained indicate that in complexes
A. A. KURGANOV et 01.
(b)
(a)
Fig. 3. CD spectra of mixed complexes HMC and TFC in methanol (A) and hexane (B). (1) Cu[(lR)-HMCb (2) Cu[(lS)-HMC]z, (3) Cu[(lS)-TFC]z, (4) Cu{[(lR)_HMCl[(lS)_TFCl},(5) Cu{[(lS)-HMCl[(lS)_TFCl}. CU(HMC)~, Cu(TFC)*
and Cu(HMI@
there
are no
noticeable inter-ligand interactions which could have caused great enantioselective effects. Axial positions of these complexes are easily accessible for the solvent molecules and the strength of the adducts formed does not depend on the optical conliguration of the ligands comprising the complex. This situation is similar to that observed for the compiexes of unsubstituted o-amino a! acids and contrasts with the properties of the complexes of N - alkyl - a! - amino acids4 No enantioselectivity was observed in studying the majority of the systems containing complexes CU(HMC)&I(TFC)~ (Fig. 3) or CU(HMC)Z-CU(HMM)~ (Fig. 4). In these cases a complete additivity of contributions of two ligands was observed, as a rule, which enter into the complex composition and the CD spectrum of the mixed complex is almost an average of the CD
(4
spectra of the initial compounds. The noticeable deviations are observed only in the system CU(~S)-(HMC)~ CU(~S)-(TFC)~ in hexane (Fig. 4b). The constant of formation of the mixed complex (log k = 1.1) points that the mixed structure is more preferred than the initial ones. At the same time the CD spectrum of the corresponding diastereoisomeric structure Cu( lR)HMC( lS)-(TFC) is intermediate between the CD spectra of the initial complexes and therefore, we cannot find the constnat of its formation. Thus, no quantitative information can be obtained about the possible difference in stability of these mixed-ligand diastereoisomeric structures.
(1) Preparation of (1R); (1s) and (lR,lS)-hydroxymethylene camphor, (lS)-trifluoroacetyl camphor and
(b)
Fig. 4. CD spectra of mixed complexes of HMC and HMM in methanol (A) and hexane (B). (1) Cu[(lR)-HMC]2, (2) Cu[(lS)_HMCl2,(3) Cu[(lR)HMMl2, (4) Cu{[(lR)_HMCIt(lR)_HMM&(5) Cu{[(lSbHMCI[(lR>-HMl.
41
Tbe study of enantloselectivlty in copper complexes Table 1. Elemental analyses of synthesized complexes found (calculated) Complex 1. Cu[(lR)-HMC]z 2. Cu[(lS)-HMC]z 3. Cu[(lR,lS)-HMC]* 4. Cu[(lR)-TFC]z 5. Cu[(lS)-TFC]z 6. Cu[(lR,lSbTFC]r 7. Cu[(lR)-HMM]r 8. Cu[(AA)lz
C
H
CU
62.5(62.6) 62.4(62.6) 62.1(62.6) 51.5(51.7) 51.2(51.7) 51.4(51.7) 62.0(62.0) 46.0(45.5)
7.0 (7.1) 6.9 (7.1) 6.9 (7.1) 4.9 (5.0) 4.8 (5.0) 5.2(5.0) 8.2 (7.9) 5.5 (5.3)
15.5(15.1) 15.3(15.1) 14.5(15.1) 11.2(11.3) 11.5Gl.3) 11.7Gl.3) 15.2(14.9) 24.4(24.3)
(lR)-hydroxymethylene menthone was performed as described in Refs. l&12. The products obtained were purified by either steam distillation (hydroxymethylene camphor) or vacuum distillation. (2) Copper complexes with the synthesized ligands were prepared as described in Ref. 13 and puritied by recrystallization from dioxane (for HMC) or by sublimation in uacuo (for HMM and TFC). The data of the elemental analyses are given in Table 1. Acetylacetonate complex of copper was synthesized as described in Ref. 14 and purified by recrystallization from a mixture of methanol with chloroform. The data of the elemental analyses are given in Table 1. (3) CD spectra of the complexes were recorded on the automatic spectropolarimeter “J-20 JASCO” (Japan) at a concentration of 5 x lo-” mol/l (in the visible region) or 5 x lo-” mol/l (in the UV region). The absorption spectra were recorded on the automatic spectrophotometer (GDR) at the same concentrations. (4) Mixed complexes were prepared in solution by mixing the solutions of two different individual complexes. The constants of the formation of mixed complexes_and their spectra were calculated by following the _ .__.-_. procedure described in Ref. 4.
F 20.2iO.4) 20.0(20.4) 20.7QO.4) -
REFERRNCES
‘L. D. Pettlt and R. J. W. Wofford. In Metal Ions in Biological Systems (Edited by H. Sigel), Vol. 9. Marcel Dckker, New York (1979). *V. A. Davankov, S. V. Rogozbln and A. A. Kurganov, Russ. Chem. Rev. 197443,764. ‘V. A. Davankov, Adu. in Chromatography (Edited by J. C. Giddings, E. Grusbka, J. Caxes and P. R. Brown), Vol. 18, p. 139.Marcel Dckker, New York, 1890. ‘v. A. Davankov, S. V. Rogozbin, A. A. Kurganov and L. Ya. Zhucbkova, J. Inora. Nucl. Chem. 1975.37.369. ‘A. A. Kurganov,T:M. Ponomaryova, V. A. Davankov, Jnorg. Chim. Acta 198045, L23. 6J. J. Fortman and R. E. Sievers, Coord. Chem. Rev. 19716,331. ‘K. C. Kosbi, V. V. Pathoik, Coord. Chem. Reu. 197722,371. *J. Sasaki, hf. Seikurada, M. Matsul and T. Sbiymoitsu, Bui. Chem. Sot. Jaoan 197452.245. Q. P. Graddon~andE. C. Wotton, J. Inorg. Nucl. Chem. 1%121, 49. “Beiisteins Handbuch der Grganishen Chemie, VII, 592 (1925). “Beilsteins Handbuch der Organischen Chemie, W, 568 (1925). ‘*A. L. Henne, M. S. Newman, L. L. Quill and R. A. Staniforth, J. Am. Chem. Sot. 1947,69, 1819. ]~BeiIsteinsHandbuch der Grganischen Chemie 1,781 (1928). “A. A. Kurganov, L. Ya. Zbucbkova and V. A. Davankov, J. Inorg. Nucf.Chem. 1978,40,1081.
THE STUDY OF ENANTIOSELECTIVITY IN COPPER COMPLEXES WITH SOME 1,3-DICARBONYL LIGANDS BY CIRCULAR DICHROIS~ SPECTROSCOPY A. A. KURGANOV,* L. YA. ZHUCHKOVA and V. A. DAVANKOV
NesmeyanovInstitute of Organo-ElementCompounds,U.S.S.R. Academyof Sciences, 117813Moscow, U.S.S.R. (Receioed 10 June 1982) Abstract-The circular diehroism spectra of copper(H) complexes with hydroxymethylene camphor, hydroxymethylene menthone, and trifluoroacetyl camphor as well as of mixed-&and complexes with acetylacetone have been studied in different solvents at different temperat~es. The changes observed in the spectra are attributed to a strong coordination of the soivent molecules in axial positions of square-planar complexes. It has been shown that the contributions of two ligands to the net spectrum of circular dichroism are additive and that the absorption spectraof the complexes do not depend on the optical configuration of the ligands. The conclusion has been drawn that no noticeableinter-@andinteractionsexist in the complexesand no en~tioselective effects are exhibited.
INTRODUCTION Enantioselective effects in labile coordination compounds attract attention of many researchers due to an important role which they play in a number of biological systems’ and in connection with the development of the method of lied-exchange c~omato~aphic resolution of racemic compounds.2’3The most part of investigations in this field involves amino acid ligands’~* whereas information on ligands of other types is much more limited. In previous papers we have considered the reasons for enantioselectivity in coppe~1~ complexes with N - alkyl - a: - amino acids4 and 1,2-diamines.5 In this report we present the results of studying enantiosele~tivity in copper(H) complexes with 3-hydroxymethylene camphor (HMC), 3-trifluoroacetyl camphor (TFC), and 2-hydroxymethyl menthone (HMM).
Complexes of ~ansition metals with 1,3-dic~bonyl ligands were the object of numerous studies and are covered in several reviews.6.’ These papers, however, give only min~um attention to &optical properties of Cu(II) complexes with HMC, TFC and HMM which, in our opinion, deserve thorough investigation. RESULTSANDDISCUSSION I. CD spec~rff of co~p~e~es
As is seen from Fig. 1, the spectra of circular dichroism (CD) of copper complexes with HMC, TFC, and HMM are characterized by l-2 bands in the region of d-d ~ansitions of CufII) atom and by a number of bands in a shorter wavelength region. Such a shape of the CD *Author to whom correspondence should be addressed. ?The data obtained mainly, for different ~~ogen~on~i~~ axial ligands.
spectrum, as is now welf known, is related to the formation of a pseudo~omatic chelate ring in the complexes of l,$diketones and is caused by considerable delocalization of n-electron system of ligands. We considered it interesting to study the effect of solvent and temperature on the shape of the CD spectrum, In aprotic non-polar solvents (hexane, toluene) the bands at - 560 and - 700 nm have a maximum intensity. The intensity decreases in solvents capable of coordination in axial positions of square-planar complexes ~me~anol, acetone, dioxane, a~eto~~le). In the UV region the solvent effects weakly the shape of the CD spectra of Cu(HMQ and Cu(TFQ whereas in the case of Cu~HM~* this effect is strongly pronounced and the transition from acetonitrile to hexane results in an almost complete disappearance of the band at - 340 nm and in a sign change of the band at -4OOnm. It should be, however, noted that correlation with the type of the solvent for Cu(HMM)* is less pronounced than for Cu(HMQ and Cu(TF&. Temperature practically does not affect the shape of the CD spectra: the most sensitive to a temperature change proves to be the band at -~nm whose intensity (in the case of Cu(HMC)*) decreases by about 20% with a temperature rise from 25 to 55” (in methanol). The intensity of other bands changes by only 5-R%. The fact that there is no correlation between the dependence of the CD spectra on the type of the solvent and temperature in a readily coordinating solvent may be explained if the eq~ibrium between a square-plans complex and its adduct with the solvent is almost completely shifted towards adduct and does not depend on temperature. This conclusion is supported by data in the literaturep” showing that the formation constant of such adducts with a composition 1: It is - 10” for Cu(HMQ and Cu(HMM), and -1031/mol for Cu(TF&. Since the solvent concentration is high, these values correspond to almost qu~ti~tive formation of the adduct in solution. Thus, the changes observed in CD spectra of Cu(HMQ2 and Cu(TFC&, when passing from non-coordinating solvents to coordinating ones, are probably due to the fo~ation of adducts with the solvents and refer, mainly, to the region of d-d transitions. As regards 37
A. A. KURGANOV et al.
,E
4
Al io.4
fO.3
+0.2
.
+4.
u
+2
.o.-
0
-2
.
-0.
-4,c 1’
-6.c
-0.
-0.3
I-
Fig. l(a).
c
P
i
/
_
c
-6.C
,
Fig. l(b).
The studyof euautioselectivity in coppercomplexes
39
Pi
+lO +8
+6
,-
Fig. l(c). Fii. 1. CD spectraof the complexesCu[(lS)-HMC]2 (A), Cu[(lS)-TFC]2 (B), Cu[(lR)-HMMJ2 (C) in Mereot solvents:1, hexane;2, methanol;3, dioxane;4, acetooe;5, tolueoe;6, acetonibile.
Cu(HMl& whose ligands are conformationally more labile than the ligands of camphor derivatives, the formation of adducts, is most likely accompanied by conformational changes and the effect of the solvent manifests itself in the whole region of wave lengths from 200 to 700 nm. 2. Enantiosefectiuity in complexes CU(HMC)~,CU(TFC)~ and Cu(HMM)2 Enantioselectivity in complexes of the ML type arises when there is a mutual effect between two ligands entering into the complex. This mutual effect appears in different forms. Thus, for instance, in the case of complexes of N - alkyl - a - amino acids” it manifests itself in the ditIerent ability of the complexes containing two ligands of identical or opposite cot&nation, to the addition of a solvent molecule in the axial position of Cu2+. In the CD spectra the mutual effect of the ligands appears as a deviation from additivity of the contributions of both ligands into the net CD spectrum. To detect the deviations from the additivity of contributions, we have studied CD spectra of mixed complexes in which HMC, HMM, or TFC was one of the ligands and the acetylacetone (AA) molecule was the second ligand. Acetylacetone is one of the smallest liiands of the 1,3-dicarbonyl type and one may expect that no noticeable steric interactions with the second lid will take place. Only in the case of CU(HMC)~ small deviations in the region -620nm were detected
-0.2-0.4.
IQ. 2. CD spectraof mixed complexesCuj[(lS)-HMCl(AA)}, 1,3-initialcomplexes,2-mixedcomplex.Chloroform as a solvent. (Fig. 2). The formation constant of mixed complex is also close to 4 which means that distribution of the ligands in the system Cu(HMCkCu(AA)&$HMC)(AA) is almost statistical in nature. The absorption spectra of C~IK~R)-(HMC)]~,Cu[(lS& (HMCIIZ and CuI(lR,lS)-(HMC)12 as well as of Cu[(lR)TFC$, Cu[(lS)-TFC12 and Cu[(lR,lS)-(TFC)], are completely identical; the differences between them are within the limits of accuracy of the measurements. All the results obtained indicate that in complexes
A. A. KURGANOV et 01.
(b)
(a)
Fig. 3. CD spectra of mixed complexes HMC and TFC in methanol (A) and hexane (B). (1) Cu[(lR)-HMCb (2) Cu[(lS)-HMC]z, (3) Cu[(lS)-TFC]z, (4) Cu{[(lR)_HMCl[(lS)_TFCl},(5) Cu{[(lS)-HMCl[(lS)_TFCl}. CU(HMC)~, Cu(TFC)*
and Cu(HMI@
there
are no
noticeable inter-ligand interactions which could have caused great enantioselective effects. Axial positions of these complexes are easily accessible for the solvent molecules and the strength of the adducts formed does not depend on the optical conliguration of the ligands comprising the complex. This situation is similar to that observed for the compiexes of unsubstituted o-amino a! acids and contrasts with the properties of the complexes of N - alkyl - a! - amino acids4 No enantioselectivity was observed in studying the majority of the systems containing complexes CU(HMC)&I(TFC)~ (Fig. 3) or CU(HMC)Z-CU(HMM)~ (Fig. 4). In these cases a complete additivity of contributions of two ligands was observed, as a rule, which enter into the complex composition and the CD spectrum of the mixed complex is almost an average of the CD
(4
spectra of the initial compounds. The noticeable deviations are observed only in the system CU(~S)-(HMC)~ CU(~S)-(TFC)~ in hexane (Fig. 4b). The constant of formation of the mixed complex (log k = 1.1) points that the mixed structure is more preferred than the initial ones. At the same time the CD spectrum of the corresponding diastereoisomeric structure Cu( lR)HMC( lS)-(TFC) is intermediate between the CD spectra of the initial complexes and therefore, we cannot find the constnat of its formation. Thus, no quantitative information can be obtained about the possible difference in stability of these mixed-ligand diastereoisomeric structures.
(1) Preparation of (1R); (1s) and (lR,lS)-hydroxymethylene camphor, (lS)-trifluoroacetyl camphor and
(b)
Fig. 4. CD spectra of mixed complexes of HMC and HMM in methanol (A) and hexane (B). (1) Cu[(lR)-HMC]2, (2) Cu[(lS)_HMCl2,(3) Cu[(lR)HMMl2, (4) Cu{[(lR)_HMCIt(lR)_HMM&(5) Cu{[(lSbHMCI[(lR>-HMl.
41
Tbe study of enantloselectivlty in copper complexes Table 1. Elemental analyses of synthesized complexes found (calculated) Complex 1. Cu[(lR)-HMC]z 2. Cu[(lS)-HMC]z 3. Cu[(lR,lS)-HMC]* 4. Cu[(lR)-TFC]z 5. Cu[(lS)-TFC]z 6. Cu[(lR,lSbTFC]r 7. Cu[(lR)-HMM]r 8. Cu[(AA)lz
C
H
CU
62.5(62.6) 62.4(62.6) 62.1(62.6) 51.5(51.7) 51.2(51.7) 51.4(51.7) 62.0(62.0) 46.0(45.5)
7.0 (7.1) 6.9 (7.1) 6.9 (7.1) 4.9 (5.0) 4.8 (5.0) 5.2(5.0) 8.2 (7.9) 5.5 (5.3)
15.5(15.1) 15.3(15.1) 14.5(15.1) 11.2(11.3) 11.5Gl.3) 11.7Gl.3) 15.2(14.9) 24.4(24.3)
(lR)-hydroxymethylene menthone was performed as described in Refs. l&12. The products obtained were purified by either steam distillation (hydroxymethylene camphor) or vacuum distillation. (2) Copper complexes with the synthesized ligands were prepared as described in Ref. 13 and puritied by recrystallization from dioxane (for HMC) or by sublimation in uacuo (for HMM and TFC). The data of the elemental analyses are given in Table 1. Acetylacetonate complex of copper was synthesized as described in Ref. 14 and purified by recrystallization from a mixture of methanol with chloroform. The data of the elemental analyses are given in Table 1. (3) CD spectra of the complexes were recorded on the automatic spectropolarimeter “J-20 JASCO” (Japan) at a concentration of 5 x lo-” mol/l (in the visible region) or 5 x lo-” mol/l (in the UV region). The absorption spectra were recorded on the automatic spectrophotometer (GDR) at the same concentrations. (4) Mixed complexes were prepared in solution by mixing the solutions of two different individual complexes. The constants of the formation of mixed complexes_and their spectra were calculated by following the _ .__.-_. procedure described in Ref. 4.
F 20.2iO.4) 20.0(20.4) 20.7QO.4) -
REFERRNCES
‘L. D. Pettlt and R. J. W. Wofford. In Metal Ions in Biological Systems (Edited by H. Sigel), Vol. 9. Marcel Dckker, New York (1979). *V. A. Davankov, S. V. Rogozbln and A. A. Kurganov, Russ. Chem. Rev. 197443,764. ‘V. A. Davankov, Adu. in Chromatography (Edited by J. C. Giddings, E. Grusbka, J. Caxes and P. R. Brown), Vol. 18, p. 139.Marcel Dckker, New York, 1890. ‘v. A. Davankov, S. V. Rogozbin, A. A. Kurganov and L. Ya. Zhucbkova, J. Inora. Nucl. Chem. 1975.37.369. ‘A. A. Kurganov,T:M. Ponomaryova, V. A. Davankov, Jnorg. Chim. Acta 198045, L23. 6J. J. Fortman and R. E. Sievers, Coord. Chem. Rev. 19716,331. ‘K. C. Kosbi, V. V. Pathoik, Coord. Chem. Reu. 197722,371. *J. Sasaki, hf. Seikurada, M. Matsul and T. Sbiymoitsu, Bui. Chem. Sot. Jaoan 197452.245. Q. P. Graddon~andE. C. Wotton, J. Inorg. Nucl. Chem. 1%121, 49. “Beiisteins Handbuch der Grganishen Chemie, VII, 592 (1925). “Beilsteins Handbuch der Organischen Chemie, W, 568 (1925). ‘*A. L. Henne, M. S. Newman, L. L. Quill and R. A. Staniforth, J. Am. Chem. Sot. 1947,69, 1819. ]~BeiIsteinsHandbuch der Grganischen Chemie 1,781 (1928). “A. A. Kurganov, L. Ya. Zbucbkova and V. A. Davankov, J. Inorg. Nucf.Chem. 1978,40,1081.