Ingle, D. B.

Khanolkar, D. D.

English

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ladiaD JOW'llal of ChemistryVo.'. {4A. Au'ust 1976, PRr :5%-5,SPotentiometric Studies of, Complex .Formation of Mn(II),Co(lI),Ni(H), Cu{II) & Zn(II) .with o-Hydroxyacetophenone Oxime &Its Derivatives' ; '.I.D. B. INGLE & ·D. D. KHANOLKARDepartment of Chemistry. Marathwada University. AurangabadReceived 21 September 1974; revised 5 November 1975; accepted'20 November 1975The stability constants of Mn(II), Co(II), Ni(II), Cu(U) and Zn(II) complexes of some substi-tuted o-hydroxyacetophenone oximes have been determined potentiometrically in water-dioxane(25-75%v/v) at Il'-O"lM (NaCI04) and 30±O·lo using the Bjerrum-Oalvtn pH titration technique asadopted by Irving and Rossotti. The validity of (i) linear relations between metal-Iigand stabilityconstants and proton-Hgand stability constants, (U) Irving-Williams order, and ({ii) Hammettequation have been examined for 1: 1 complexes. . 'THOUGH the formation of metal chelates ofo-hydroxyacetophenone oxime, resacetophe-none oxime and 2-hydroxy-5-methylaceto-phenone oxime has been indicatedt+ but these studieswere mainly concerned with the use of those reagentsas analytical reagents. The present work deals witha systematic potentiometric study of proton-ligandconstants of some substituted o-hydroxyacetophe-none oximes and stability constants of its chelateswith transition metal ions.Materials and MethodsThe details regarding preparation of ligands andthe experimental technique employed for theBjerrum-Calvin titration are given in an earliercommunications,Metal Salt SolutionsIn view of the ability of SO:- ion to complex tothe same extent with the metal ions studied in thepresent investigation and comparatively high themetal-ligand stability, it was considered desirableto employ sulphates of transition metal ions (BDH.Analar) for the present study". The solution ofCu(II) and Ni(II) were standardized by titratingthe metal solutions with aq. sodium EDTA usingmuroxide as an indicator. Mn(II) and Zn(U) wereestimated using Erio. T indicator as described bySchwarzenbach7.The amount of Co(U) was deter-mined by the method followed by Schwarzenbach".CalculationsFor the calculation of stability constants it wasassumed that factors like hydrolysis of metal ionsand presence of polynuclear hydrogen and hydroxylbea.ring complexes were absent. The assumptionswere justified on the following grounds: (i) Thesolutions employed being very dilute, the probabilityof polynuclear species under experimental conditionswas not expected to be significantly high, (ii) themetal-reagent curves show departure from thereagent curve at B values (PH meter readings) muchlower than the B values of hydrolysis of metal ions,596and (iii) the metal-ligand stability constants beingcomparatively very high, the anion complexingwill not vitiate the relative stability values becausethis factor remains common throughout. Valuesof n-(metal-ligand formation number) were calculatedusing the Irving-Rossetti" expression.Cobalt(II) system - The B values of hydrolysisof Co(U) was 5·5. The departure of metal-complextitration curve from the reagent curve commencedat B = 2·75. The variation of n was continuousand symmetrical up to' B = 6·5. The highest valueof ii was 2 before hydrolysis commenced. Thisindicates formation of 1:1 and 1:2 complexes. Theformation curve was not symmetrical. The partof the curve between 0 < n < 2 was treated by thepointwise calculation. The values showed conti-nuous drift. The log K values were calculated by themethod of pointwise calculation log Kl = log nt(l-ii) +pHL, log K2 = log (n-1){(2-ii) +pHL andthe half integral method.Manganese(II) system"':"-The B value of hydrolysisof Mn(II) could not be determined accurately as thesolution became opaque at B = 5·6. The deviationof metal complex titration curve from the reagentcurve was observed from B = 3·7 to 4,5, dependingon the reagent. The variation of 11,is continuousand symmetrical up' to B = 6. The highest valueof ii was 2 with, a few ligands, while with most ofthe ligands the maximum value of n WClS 1·00. Themethods of pointwise calculation and of half integralswere used for the calculation of log K values,Nickel(II) system - The B of hydrolysis of Ni(II)was 7. The departure of metal-complex titrationcurve from the reagent curve was seen from B = 5.The variation of ii was continuous and symmetricalup to B = 7, and then changed abruptly. Valuesof ii greater than unity were observed at and abovethe B value of hydrolysis. This indicated the for-mation of 1:1 complex and that of 1:2 complex wasuncertain. The log K values for 1:1 complex wereobtained by the method of pointwise calculation.Copper (II) systems - It was observed that (i) inall copper systems, except in the case of 2-hydroxy-5-INGLE & KHANOLKAR: COMPLEXES OF Mn(Il), Co(II), Ni(U), Cu(Il) & Zn(Il)TABLE 1 - METAL-LIGAND STABILITY CONSTANTSLigand log P l\J.j NIn(II) Co(II) Cu(II) Zn(II)log KNi(II)log K,OHAPORAPO5-Methyl-OHAPO3-11ethyl-OHAPO5-Chloro-OHAPO5-Bromo-OHAPO3-Chloro-OHAPO3-Bromo-OHAPO5-lodo-OHAPO5-Xitro-OHAPOlog I{l log K2 log Kl log K2 log K, log no11·86 10·26 /·92 11·43 9·43 7·80 10·99 10'4211·14 9·24- 6·04- 10·65 7·29 8·23 11·10 10'6712·11 7·86 9·20 8·11 8·14 11·33 10·7112·05 8·67 8·89 7·97 11·47 10·9311·28 9·06 6·54 11·17 7·57 7·59 10·77 10·34-11·27 9·30 7·65 11·22 8·34- 7·57 10·78 10·1710'77 7·78 10·35 7·20 7·97 10·99 9·0111·04- 9·66 10·37 7·69 8·02 11·19 10·1211·16 8·31 11·04- 7-41 7·44- 10·68 9·978·97 6·17 9·26 6·39 6·36*Takell from an earlier paper [Indian J. Chem., 13 (1975), 605:.OHAPO = o-hydroxyacetophenone oxime; RAPO = resacetophenone oxime.9·198·468·859·038'428·267·798·24-8·095·53nitroacetophenone oxime where precipitation wasnoticed at B = 2·2 and measurements were notcarried out, a distinct colour change was observedon the addition of reagent around B = 3-4, (ii) thedeparture of metal-complex titration curve fromthe reagent curve was always seen at B values lessthan B of hydrolysis, 4·9 and (iii) the highest valueof ii was around 1'8, indicating the formation of 1:1and 1:2 complexes. The hydrolysis effects wereignored while calculating the metal-ligand stabilityconstants as the complex formation took place ata lower B value than that of hydrolysis.The values in low ii and [L] range are not availableand even if obtained would be suspect on accountof anion complexing at the low B values. Thispermits the use of only He least squares treatmentor pointwise calculation method of Hearon andGilberts. In the latter method log K1K2 is obtainedeither by least squares method-? using Eq. (1).1i (2-ii)[L], •(ii-1)[LJ = (1i-1) KIK2-B..l ... (1)or from the relation log KIK2 = 2 PHLn-1 andlog Kl is then calculated using Eq. (2).K1 = (2-ii)\L]2K1K2-ii ... (2)[L, (1i-l)The least square value of log Kl was too low ascompared to most of the corresponding values ob-tained by the pointwise calculation. This dis-crepancy is due to negati ve values of log Kl at ii< 0·5 which were obtained ill the calculations carriedout assuming log K1K2 = 2 PHL1i=I' These negativevalues might be either due to inaccuracies in theestimation of ii at such low B values where \'(3) -\'(2)is quite small or due to anion complexing at low Bvalues of the order of 3. This would cause the ex-perimental values of ii to be lower than the trueones.In the treatment by the method of least squares,it has been suggested that the values are betterestimated with the help of the slope rather than theintercept. The value of log KIK2 was, therefore, ob-tained by this method. log K2 was obtained by thepointwise calculations independently. The value oflog J(1 was then obtained by taking the difference.The values of log Kl and log K2 so obtained are inagreement with those obtained from the half-integralmethod.Zinc(ll) system - The deviation of metal complextitration curve from the reagent curve starts atB = 5·5. The value of ii = 1 at B value of hydro-lysis 6'1, show the formation of only 1:1 complex.Results and DiscussionThe metal-ligand stability constants of thevarious metal systems studied presently are givenin Table 1.Relation between log Kl and log PK!j (PK~) - Thevalidity of the linear relation between metal-ligandstability constants and proton-ligand stability con-stants has been examined for transition metal com-plexes of substituted o-hydroxyacetophenone oximes(OHAPOs) by plotting log Kl against log PKf,It will be be seen a single line passing through allthe points is not possible. In particular, thepoints corresponding to 5-methyl-, 3-methyl-, 5-uitro-,3-chloro- and 3-bromo-OHAPOs show significantdeviation from linearity. Jones et alP have sug-gested that correlations of this type are not generallyvalid. In the present case for oxirnes with disso-ciation constants close to each other the points,roughly fall on a linear plot, while 5-methyl-,3-.methyl~ and 5-uitro-OHAPOs whose log PKlf areWIdely different, the points deviate from linearity.However deviation from linearity exhibited 3-chloro-and 3-bromo-OHAPOs may be due to steric inter-action.Relation bettaeen log K values of iieo similar metalions '/.i:ith the same ligan d. - A comparison of themetal-ligand stability constants of two similar metalshaving the same coordination number was suggestedby Irving and Rossot tit", Plots obtained for thesystems Cu(II)-Zn(II), Cu(U)-Ni(U), Mn(U)-Zn(II)and Ni(II)-Zn(U) show that except for Cu(U) com-plexes the relation of Freiser and coworkers= doesnot show much improvement over the log Kl versuspKoH relation.Irving-Williams order for stability constants - Thelog K values of the metal complexes do not followthe Irving-Williamsw order. They also do not597INDJAN J. CHEM., VOL. HA, AUGUST 1976agree with the order of the pH values of incipientprecipitation of metal ions given by Flagg. andFurmanw for salicylaldoximeor by Bandyopadhayayaand Rayl8 for salicylamidoxime.The Irving-Williams order which is essentiallythe order of crystal fieldstabilization energies (CFSE)of transition metal ions will ideally hold foroctahedral spin-free transition metal complexes ifthe various factors such as metal ligand bondenergies, polarization energies of the Iigands, hydra-tion energies, etc., contributing to standard enthalpychange, vary uniformly, except. the differences inligand field stabilization energies. The work onsolid transition metal complexes of substituted,OHAPOSl7indicated that Cu(U), Ni(U) and Co(II)complexes are square planar and the last two arespin-paired. The exceptions to the Irving-Williamsorder have been attributed to spin-pairing in strongcrystalfields as one of the probable causes since thisfactor influences the relative CFSE in a differentway than in spin-free complexesv. Further, Co(H)and Mo(U) ions are known for their tendency to getoxidized in! alkaline medium in the presence ofnitrogen donors. It, therefore, appears that unlessQUe has exact knowledge of the contribution ofvarious factors which influence the CFSE of metalcomplexes, it would be futile to discuss the orderof stability constants vis-a-vis the Irving-Williamsorder.Application of Hammett equation to metal-ligandsystem - May and Jonesl' on the lines of theHammett relation proposed the relation log KIKo= G for metal-complexes, where K and KO are thestability constants of the complexes with substitutedand unsubstituted acids, G is Hammett constantand G is a constant characteristic of the reaction.They found that the above relation was valid forseventeen Cu(II) complexes of substituted benzoicacids but failed fora series of pyridine adducts of'Cu(II) acetyl acetonates. Tate and JonesliO alsocould not get a satisfactory linear relation forsulphonate complexes of cadmium. The va~uesof G were obtained by Hammett from a great varietyof data and have, in some cases, a rather large pro-babilit spread.. These values for dioxane-watersolvent are not available. .It was, therefore, thought598that one couldjustify the use of alternative G valuesgiven by the ratio of dissociation constants ofsubstituted OHAPOs to that of OHAPO. TheseG values were employed to test the linear relationsuggested by May and Jones. It was found thatthe points corresponding to 5-methyl-, 5-chloro-,5-bromo- and 5-iodo-OHAPOs roughly fall on alinear plot and those corresponding to 3-methyl-,3-chloro-, 3-bromo- and 5-nitro-OHAPOsshow signi-ficant deviation from linearity. The deviation ob-served in the case of first three oximes may beattributed to the ortho effect. The nitro substitutedcompound gives anomalous results probably becauseof the possibility of direct conjugation of the nitrogroup with the phenoxide ion.References1. KABADI, M. B, & VENKATACHALAM, K. A., Curr. Sci .•27 (1958), 337.2, PODDAR, S. N., Indian J. Chem; 1 (1963). 496; 537.3. SHARMA, H. K., Indian J. appl. cu«; 28 (1964), 43.4. PATEL, R. P. & PATEL, R. D., J. inorg . nucl. Chem., 32(1970), 2591. .5. INGLE, D. B. & KHANOLKAR, D. D., J. Indian chem,Soc., 50 (1973), 103.6. BJERRUM, J., Chem. m«, 46 (1950), 38t.7. SCHWARZBNBACH, G., Comp'exomet,ic titrations (Methuen& Co, Ltd, London), 1957, 69; 76; 79; 82.8. IRVING, H. & ROSSOTTI, H., J. chem. s». (1953),2904.9. HEARON, J. Z. & GILBERT, J. B., J. Am. chem, Soc., 77(1955}, 2594.10. SCARBOROUGH, J. B., Numerioa; mathematical analysis(Oxford University Press), 1930, 364.11. JONES, J. G., TOMKINSON, J. C., POOLE, J. B. & WILLIAMS,R. J. P., J. chem. Soc., (1958), 200t.12. FREISER, rr; FERNANODO, Q. & CHENEY, G. E., J. Phys.Chem. Ithaca, 63 (1959), '250.13. IRVING, H. & ROSSOTTI, H., Acta cbem, scand., 10(1956), 72.14. IRVING, H. & WILLIAMS, R. J. P., Natu,e, 162 (1948), 746.15. FLAGG, J. F. & FURMAN, N. H., Ind. Engng chem. Anal.Ed" 11 (1940), 529, 663.16. BANDYOPADHAYAYA, D. & RAY, P., J. Indian chem,ss«, 33 (1956), 21, 65.17. KHANOLKAR, V. D., Ph.D ..thesis, Marathwada University,Aurangabad, 1973.18. COTTON, F. A. & 'VILKINSON, G., Advanced inorganiacheMistry (Interscience, New York], 1966, 690.19. MAY, W. R. & JONES, M. M., J. inorg, nucl. Chem.,24 (1962), 511; 2S (1963), 507.20. TATE, J. F. & JONES, M. M., J. Am. chem. Soc., 83 (1961).3024.

Potentiometric Studies of, Complex Formation of Mn(II),Co(II), Ni(II), Cu(II) & Zn(II) with o-Hydroxyacetophenone Oxime & Its Derivatives

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Potentiometric Studies of, Complex Formation of Mn(II),Co(II), Ni(II), Cu(II) & Zn(II) with o-Hydroxyacetophenone Oxime & Its Derivatives

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