K~::~:~~ K~::~~~g~ K~~:~~g! L K~!L) - NISCAIRnopr.niscair.res.in/bitstream/123456789/54205/1/IJCA...
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MixedLigand Complexes of Ni(II) & Cu(II) with Histidine & Iminodlacetlc Acid as Primary Ligands & Glycine, a-Alanine, p-Alanine, Leucine & Isoleucine as Secondary Ligands J. D. JOSHI Chemistry Department, Shri R.K. Parikh Science College Petlad, Gujarat Received 27 September 1975; revised 23 February 1976; accepted 26 April 1976 Formation constants (Iog K~!L) ofmixed Iigand com- plexes, where M=Ni(U) or Cu(U), A=histidine or Imlnodiaceticacid and L=~lycine, a-alanine, l}-alanine, leucineand isoleucine, have been determined ustng a modifiedform of Irvlng-Rossottl titration technique. Thevalue of mixed Iigand formation constant K~!L.is lowerthan K~ for the binary complexes. This may be becauseofcharge repulsion between the primary ligand andsecondary Iigand, BHATTACHARYA and coworkers have investi- gated 1 • 2 the mixed ligand system (MAL) involving bivalent metal ions like Cu 2 +, Ni2+, Zn 2 + and histidine (Hist.), iminodiacetic acid (IMDA) or nitrilotriacetic acid (NTA) as primary ligand and polyhydroxy- phenols or amino acids as secondary ligands. In the present investigation formation constants of the title systems have been determined employing modifiedform of Irving-Rossetti titration technique. All the reagents used were of AR quality. The metal perchlorates were prepared from their res- pective carbonates and their metal contents deter- mined by standard methods. The experimental set-up and calculations described by Bhattacharya and coworkers- were employed. The measurements were carried out at 30°. The interpretation of the potentiometric curves was similar to that reported by Bhattacharya and coworkers'. nand PL were calculated by the equation used earlier by Mavani et al". Precise values of K~~L were determined by the method of averages", and the results are presented in Table 1. Cu.hist.L system could not be studied as histidine forms a solid complex with Cu(II) at low pH. The order of the formation constants of the ternary complexes is the same as for the binary complexess-". However, the values of KR1*L are significantly lower' than the values of first forma- tion constant Ktk of the binary complexes and are nearly equal to second formation constant KhL. of the binary complexes. The order of mixed ligand f t · t t d '. KM.(Hist) KM.(IMDA) orma ion cons an or er IS. M.(Hist)L > M.(IMDA).L' This can be explained by considering that the electrostatic repulsion between the primary ligand and the secondary ligand goes on increasing with the increase in the charge on the primary ligan d. The values of the formation constants of the mixed ligand complexes [Ni.hist.L] are nearer to those of [Ni.IMDA.LJ though histidine has one negative chargeand IMDA has two negative charges. How- ever, histidine being bulkier molecule offers more steric hindrance to the incoming secondary ligand. NOTES TABLE 1- MIXED LIGAND FORMATION CONSTANT OF SOME HETEROCHELATES OF Cu(II) AND Ni(II) AT 30° log K~::~:~~.L log K~::~~~g~_L log K~~:~~g!_L Glycine e-Alanine Leucine Isoleucine 4·90±0·02 4'65±0'02 4·57±0·02 4'55±0'02 4-85±0'03 4·59±0·02 4·34±0·02 4·51 ±0·02 6·18±0·03 5·17±0·02 6·27±0·01 6·12±0·03 This, besides, charge repulsion other factors may also affect the mixed ligand formation constant. (j- Alanine forms a six-membered chelatering which is more strained. Therefore, the complexes of (j- alanine are less stable. References 1. MAVANI, 1. P., JEJURKAR, C. R. & BHATTACHARYA, P. K., Indian J. Chem., 10 (1972), 742. 2. CHIDAMBARAM, M. V. & BHATTACHARYA, P. K., Acta chim. hung., 75 (1975), 123. 3. MAVANI, I. P., ]EJURKAR, C. R. & BHATTACHARYA, P. K., J. Indian chem, Soc., 49 (1972), 469. 4. DUBEY, S. N. & MEHROTRA, R. C., J. Indian chem. Soc., 43 (1966), 73. 5. CHIDAMBARAM, M. V. & BHATTACHARYA, P. K., J. Indian chem. Soc., 47 (1970), 833. 6. CHIDAMABARAM, M. V. & BHATTACHARYA, P. K., Indian J. Chem., 7 (1969), 282. Mixed Ligand Complexes of Th(IV) with Diethylenetriaminepentaacetic Acid (DTPA) as a Primary Ligand & Ethylenediamine & Propylene-Lz- & -1,3-Diamines as Secondary Ligands O. P. PACHAURI & J. P. TANDON Department of Chemistry, University of Rajasthan J aipur 302004 Received 23 February 1976; accepted 26 April 1976 Solution equilibria of ternary systems of the type MAB, where M=Th(IV), A=diethylenetriaminepenta- acetic acid (DTPA), B=ethylenediamine (en), 1,2- propylenediamine (1,2-pn) or 1,3-propylenedianline (1,3-pn) have been studied potentiometrically. The nature of the titration curves indicates that the secon- dary ligand B (en or 1,2-pn) is added stepwise to the initially formed Th(IV)-DTPA chelate. However, in the case of Th(IV)-DTPA-l,3-pn system the experi- mental evidence does not support the mixed complex formation. The formation constants (log K~!B) of the mixed ligand chelates have been calculated and the order of stability in terms of secondary li~and has been found to be 1,2-pn>en. THE formation constants of the 1:1:1 Th(IV)- DTPA or CDTA-diamirJes 1 , 1:1:1 Th(IV)-DTPA- hydroxy acid 2 - 4 and 1:1:1 Th(IV)-DTPA-amino acids" have been reported by us. The resulting mixed ligand complexes containing octadentate DTPA molecule as primary ligand indicate that the central metal ion attains tenfold coordination. With a view to having an idea of the relative stabilities, these studies have been extended for the ternary systems 1:1:1 Th(IV)-DTPA-diamines and 57
Transcript of K~::~:~~ K~::~~~g~ K~~:~~g! L K~!L) - NISCAIRnopr.niscair.res.in/bitstream/123456789/54205/1/IJCA...
MixedLigand Complexes of Ni(II) & Cu(II)with Histidine & Iminodlacetlc Acid asPrimary Ligands & Glycine, a-Alanine,
p-Alanine, Leucine & Isoleucine asSecondary Ligands
J. D. JOSHI
Chemistry Department, Shri R.K. Parikh Science CollegePetlad, Gujarat
Received 27 September 1975; revised 23 February 1976;accepted 26 April 1976
Formation constants (Iog K~!L) ofmixed Iigand com-plexes, where M=Ni(U) or Cu(U), A=histidine orImlnodiaceticacid and L=~lycine, a-alanine, l}-alanine,leucineand isoleucine, have been determined ustng amodifiedform of Irvlng-Rossottl titration technique.Thevalue of mixed Iigand formation constant K~!L.islowerthan K~ for the binary complexes. This may bebecauseof charge repulsion between the primary ligandandsecondary Iigand,
BHATTACHARYA and coworkers have investi-gated1•2 the mixed ligand system (MAL) involving
bivalent metal ions like Cu2+, Ni2+, Zn2+ and histidine(Hist.), iminodiacetic acid (IMDA) or nitrilotriaceticacid (NTA) as primary ligand and polyhydroxy-phenols or amino acids as secondary ligands. Inthe present investigation formation constants ofthe title systems have been determined employingmodifiedform of Irving-Rossetti titration technique.
All the reagents used were of AR quality. Themetal perchlorates were prepared from their res-pective carbonates and their metal contents deter-mined by standard methods.
The experimental set-up and calculations describedby Bhattacharya and coworkers- were employed.The measurements were carried out at 30°.
The interpretation of the potentiometric curveswas similar to that reported by Bhattacharya andcoworkers'. nand PL were calculated by the equationused earlier by Mavani et al". Precise values ofK~~L were determined by the method of averages",and the results are presented in Table 1. Cu.hist.Lsystem could not be studied as histidine forms asolid complex with Cu(II) at low pH.
The order of the formation constants of theternary complexes is the same as for the binarycomplexess-". However, the values of KR1*L aresignificantly lower' than the values of first forma-tion constant Ktk of the binary complexes and arenearly equal to second formation constant KhL. ofthe binary complexes. The order of mixed ligandf t· t t d '. KM.(Hist) KM.(IMDA)orma ion cons an or er IS. M.(Hist)L > M.(IMDA).L'
This can be explained by considering that theelectrostatic repulsion between the primary ligandand the secondary ligand goes on increasing withthe increase in the charge on the primary ligan d.The values of the formation constants of the mixedligand complexes [Ni.hist.L] are nearer to those of[Ni.IMDA.LJ though histidine has one negativecharge and IMDA has two negative charges. How-ever, histidine being bulkier molecule offers moresteric hindrance to the incoming secondary ligand.
NOTES
TABLE 1- MIXED LIGAND FORMATION CONSTANT OF SOMEHETEROCHELATES OF Cu(II) AND Ni(II) AT 30°
log K~::~:~~.Llog K~::~~~g~_Llog K~~:~~g!_LGlycinee-AlanineLeucineIsoleucine
4·90±0·024'65±0'024·57±0·024'55±0'02
4-85±0'034·59±0·024·34±0·024·51 ±0·02
6·18±0·035·17±0·026·27±0·016·12±0·03
This, besides, charge repulsion other factors may alsoaffect the mixed ligand formation constant. (j-Alanine forms a six-membered chelatering whichis more strained. Therefore, the complexes of (j-alanine are less stable.
References
1. MAVANI, 1. P., JEJURKAR, C. R. & BHATTACHARYA, P. K.,Indian J. Chem., 10 (1972), 742.
2. CHIDAMBARAM,M. V. & BHATTACHARYA, P. K., Acta chim.hung., 75 (1975), 123.
3. MAVANI, I. P., ]EJURKAR, C. R. & BHATTACHARYA, P. K.,J. Indian chem, Soc., 49 (1972), 469.
4. DUBEY, S. N. & MEHROTRA, R. C., J. Indian chem. Soc.,43 (1966), 73.
5. CHIDAMBARAM, M. V. & BHATTACHARYA, P. K., J. Indianchem. Soc., 47 (1970), 833.
6. CHIDAMABARAM, M. V. & BHATTACHARYA, P. K., IndianJ. Chem., 7 (1969), 282.
Mixed Ligand Complexes of Th(IV) withDiethylenetriaminepentaacetic Acid (DTPA)as a Primary Ligand & Ethylenediamine &
Propylene-Lz- & -1,3-Diamines asSecondary Ligands
O. P. PACHAURI & J. P. TANDON
Department of Chemistry, University of RajasthanJaipur 302004
Received 23 February 1976; accepted 26 April 1976
Solution equilibria of ternary systems of the typeMAB, where M=Th(IV), A=diethylenetriaminepenta-acetic acid (DTPA), B=ethylenediamine (en), 1,2-propylenediamine (1,2-pn) or 1,3-propylenedianline(1,3-pn) have been studied potentiometrically. Thenature of the titration curves indicates that the secon-dary ligand B (en or 1,2-pn) is added stepwise to theinitially formed Th(IV)-DTPA chelate. However,in the case of Th(IV)-DTPA-l,3-pn system the experi-mental evidence does not support the mixed complexformation. The formation constants (log K~!B)of themixed ligand chelates have been calculated and theorder of stability in terms of secondary li~and hasbeen found to be 1,2-pn>en.
THE formation constants of the 1:1:1 Th(IV)-DTPA or CDTA-diamirJes1, 1:1:1 Th(IV)-DTPA-
hydroxy acid2-4 and 1:1:1 Th(IV)-DTPA-aminoacids" have been reported by us. The resultingmixed ligand complexes containing octadentateDTPA molecule as primary ligand indicate thatthe central metal ion attains tenfold coordination.With a view to having an idea of the relativestabilities, these studies have been extended for theternary systems 1:1:1 Th(IV)-DTPA-diamines and
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1ND1AN j. CHEM., VOL. i5A, JANUARY i977
the results presented in this note. The diaminesemployed were: ethylenediamine (en), 1,2-pro-pylenediamine (1,2-pn) and 1,3-propylenediamine(1,3-pn).
A stock solution of metal nitrate (BDH, AR) wasprepared in doubly distilled water and standardizedas described earlier", The hydrochlorides of thediamines (Riedel) were first prepared and then re-crystallized several times. Their solutions wereprepared in doubly distilled water by direct weighing.Tripotassium salt of DTPA was used for preparing itssolution in doubly distilled water. The ligand solu- ------------------------tions ",ere standardized potentiometrically againsta standard KOH solution. The ionic strength ofall the reaction mixtures was maintained constant(lL = 0·1) using O·lM potassium nitrate and low con-centrations (5X 10-3M) of the ligand and metal ion.
The hydrolysis constant (PKH) of the normal 1:1Th(IV)-DTPA chelate and the dissociation constantsof diamines were taken from the Iiterature". Theformation constants of the mixed ligand complexeswere calculated by the methods similar to thoseemployed by Thompson and Loraas".
The potentiometric titration curves of dihydro-chlorides of en and 1,2-pnindicate a small differencein their pK values and only onewell-definedinflexionat m = 1 (m = moles of alkali added per mole ofthe ligand or metal ion) in both the cases.
When the reaction mixture containing Th(IV)and the primary ligand (DTPA) in the molar ratioof 1:1 was titrated, an inflexion at m = 2 wasobserved due to the neutralization of two protonsfrom the ligand. This indicated the formation ofthe normal hydrated 1:1 Th(IV)-DTPA chelate inthe buffer region. Further addition of one mole ofalkali resulted in a secondbuffer region, whichmay beascribed to the hydrolysis of the 1:1 binary chelate''.
The potentiometric titration curves of 1:1:1Th(IV)-DTPA-en and 1:1:1 Th(IV)-DTPA-l,2-pnsystems exhibit inflexions at m = 2 and m = 4. Inboth the cases up to m = 2, the curves overlap withthat of 1:1 Th(IV)-DTPA curve indicating theformation of 1:1 binary complex in the initial stagesof titration. Occurrence of a second buffer regionbetween m = 2 and m = 4 corresponds to theneutralization of two hydrogen ions from thediamines resulting in the stepwise formation of 1:1:1mixed ligand complexes.
The formation of the mixed ligand derivatives wasfurther supported by drawing a composite curve[drawn by the horizontal addition of the 1:1 Th(IV)-DTPA curve to the respective free secondary ligandcurve], which was found to be well above the experi-mental curve between m = 2 and m = 4 in these cases.
However, in the Th(IV)-DTPA-l,3-pn system,definite support in favour of the ternary complexformation was not available from the pH-metriccurves. A similar observation was made in the caseof Th(IV)-EDTA or CDTA-l,3-pn system. In thesesystems, no appreciable lowering ofpH in comparisonto the theoretical composite curve was noted.
A comparison of the formation constants listedin Table 1indicates that the stability of mixed ligandcomplexes in terms of primary ligand follows theorder: EDTA > CDTA > DTPA and in terms ofsecondary ligands 1,2-pn > en.
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TABLE 1 - FORMATIONCONSTANTSOF 1: 1: 1 MIXED LIGANDCHELATESAT TEMP.=30o±1° AND [1.=0'1 (KN03)
System
Th(IV)-DTPA-enTh(IV)-DTPA-1,2-pnTh(IV)-CDTA-enTh(IV)-CDTA-1,2-pnTh(IV)-EDTA-enTh(IV)-EDTA-1,2-pn
4·41 ±0'084'62±0'045'30±0'08 (ref. 1)5'48 ±0'09 (ref. 1)6·55 ±0'03 (ref. 1)6·70±0·02 (ref. 1)
The lower stabilities of the ternary derivativeswith DTPA as compared to the analogous CDTAor EDTA complexes may be explained on the basisof the relative stabilities of their binary chelates".Due to the higher basicity of 1,2-pn, its complexeshave been found to be more stable than the corres-ponding en derivatives.
A plot of log K~~B against log KMA (where A =EDTA, CDTA, or DTPA, and B = en or 1,2-pn)was linear indicating that the relative stabilitiesof the ternary complexes follow the same order asthe binary complexes.
References
1. PACHAURI, O. P. & TANDON, J. P., Acta chim, hung.,86 (1975), 39.
2. PACHAURI,O. P. & TANDON, J. P., J. inorg. nucl, cu«;37 (1975), 2321.
3. PACHAURI, O. P. & TANDON, J. P., Z. Naturforsoh., 30(1975), 751.
4. PACHAURI, O. P. & TANDON, J. P., Mh. Chem., 107(1976), 83.
5. PACHAURI,O. P. & TANDON, J. P., Bull. Akad, pol. Sci.,24 (1976), 7.
6. PACHAURI,O. P. & TANDON, J. P., BUll. Akad. pol. 5ci.,22 (1974), 981.
7. SHARMA,G. & TANDON,J. P., Z. Naturforsch., 25 (1970), 22.8. THOMSON,L. C. & LORAAs, J. A., Tnorg, Chem., 2 (1963),
89.9. BOGUCKI,R. F. & MARTELL,A. E., J. Am. chem. Soc., 80
(1958), 4170.
Stability Constants of Some Transition MetalComplexes with Schiff Bases Derived from
Salicylaldehyde & m-Aminophenol orm-Anisidine
K. P. DUBEY & B. L. WAZIRDepartment of Chemistry, University of Kashmir, Srinagar
Received 13 February 1976; accepted 24 March 1976
Stability constants of a number of transition metalcomplexes with Schiff bases derived from salicylalde-hyde, and m-aminophenol (SMAP) or m-anisidine(SMA) have been determined in 50% ethanol at p.=0·05M(KNOs)' using the Calvin-Bjerrum pH titration tech-nique as modified by Irving and Rossotti. The orderof stabilities for the complexes of first row transitionmetals is: Cu2+>Fe2+>Ni2+>CoH>Zn2+> MnH. Theorder of stabilities in the case of some other tran-sition metal complexes is: CrS+>UO~+>Be2+>Nd8+>PrS+>LaS+.
