Patel, M. S.

Trivedi, T.

Vyas, D. N.

English

NOPR

Indian Journal of ChemistryVol. 15A, December 1977, pp. 1051-1053Polarographic Study of Complexation of BP+ with Schiff Bases InAcetate BufferM. S. PATEL, T. TRIVEDI & D. N. VYASDepartment of Chemistry, Saurashtra University, BhavnagarReceived 2 December 1976; accepted 24 June 1977The complexation reaction of Bi> with three Schiff bases derived from benzaldehyde, sali-cylaldehyde and vanillin and tris buffer has been investigated polarographically in acetate bufferat three different temperatures. The quasi-reversible reduction wave in each case has beengiven three different treatments due to (i) Matsuda and Ayabe, (ii) Gelftngs and (iii) Koryta tocalculate overall electrode reaction rate constant. The stability constants of the complexesand therrnodynarnic functions have .also been deterrnlned.POLAROGRAPHIC investigations on thecomplexation of Bi(III) with Schiff baseshave not been carried out so far, though afew reports on the complexes of Bi(III) and Sb(III)are availablev '. A detailed polarographic studyof Bi(III) complexes with three Schiff bases suchas benzaldehyde tris buffer (Ia), salicylaldehydetris buffer+ (Ib) and vanillin tris buffer" (Ic) has beencarried out. In view of the quasi-irreversible natureof the reduction wave, the overall electrode reactionrate constants have been calculated employing(i) Matsuda and Ayabe, (ii) Gellings and (iii) Korytatreatments.Ia:R, =Rl=R3=H:Ib:R,=OH,RrR3=Hrc;R,=H,R1=OcH3 ,R3=O HMaterials and MethodsSalicylaldehyde and vanillin tris buffers wereprepared by the literature method+, m.ps. 134° and158° respectively. Benzaldehyde tns _buffer w~sprepared employing standard method" for Schiffbases, m.p. 92°.A stock solution of Bi(III) was prepared bydissolving bismuth trichloride (AR) in gl. aceticacid and then titrated against standard titriplexIII (CLOH14N2NazOs.2H20) solution. The final solu-tion contained 0·422 mM Bi(III) in 1·0M acetatebuffer of pH 4·76, with 0·002% gelatin as themaximum suppressor. The ligands were also dis-solved in I·Oilf acetate buffer except BT which wasfirst dissolved in gl. acetic acid and then dilutedwith acetate buffer. Its complexation was studiedin 4'OM acetate buffer of pH 4·2.Polarograms of the deaerated solution were re-corded manuallv at the desired temperature (± 0.1°)using a Toshniwal polarograph type CL02A andBeltronix micro ammeter. The capillary used hadthe characteristic: m2/3 tl/6 = 2·2 mg2/3 sec-1/2 inl'OAf acetate buffer of pH 4·76 at zero applied volt-age. The average current was measured 111 eachcase against SCE.Results and DiscussionA single well-defined reduction wave was obtainedin each case. The plots of id vs h~orr were linear.The temperature coefficients of the limiting currentwere in the range 1·1 to I·6%rc. These obser-vations suggest the diffusion-controlled nature of thecurrent.Negative shifts of Et on increasing [ligand]indicate complexation. The plots of log ijid-i vsE are curved near abscissa. The values of k~vt(between 10-2 and 30) and of standard electrodereaction rate constant (between 2 x l 0-2 and 5 x l 0-11em sec-l) show the quasi-reversible nature of thereduction+-".In order to calculate the overall standard reactionrate constants (k~)B for reaction (1)[AfX"Jz+ +Ze~Jl +nX ... (1)Three different methocls were used. The valuesof (k~)B thus obtained are listed in Table 1.Matsuda and Ayabe treatment6 - The overallstandard reaction rate constant (k~)B was determinedusing Eq. (2)log (k~)B = log k;+} log (D')"+! 10g(DMx)1l+log qr~p) ...(2)All the terms in the equation were determinedas per the description given in the literature". D'and DMX are diffusion coefficients of the metal ionand complex species respectively determined fromIlkovic equation.The plot of E~ vs log ex was linear in each caseand the value ~f n was determined as 1 usingrelation (3)ZF (:.l(-ED)n = 2'3Rt" Lllog C~ ... (3)The above' fact suggests that a 1:1 complexprevails in the bulk of the solution. The ligand1051INDIAN J. CHEM., VOL. 15A, DECEMBER 1977number p of the complex actually reduced at theelectrode was found from relation (4).P = (1-) ,A. log k:(J.. n, /).log Cx ...(4)In the present case p = 0 which shows that metalion itself is reduced after dissociating from thecomplex at the electrode.The standard electrode reaction rate constant wascalculated from Eq. (5) (ref. 6){k~ls= k~.( PI . KI')/3 ... (5)I'=p+lwhere ~ = backward transfer coefficient and KI' =dissociation constant, with [J. = N, N -1, , P+1.The complex actually reduced at the electrode isassumed as Mxf:·GeUings treatmentS - Though this treatment isvalid to calculate k~ for a metal ion in non-cornplexingmedia, this was modified according to the argumentsgiven by Meites": The modification was achievedby simply introducing the ligand concentrationterm to the equation developed for the reduction.of simple metal ion.Eq. (6) given by Gellingslog k~= log A+t log D'" +t log D~x ..• (6)was modified to get Eq _ (7)log (k~h= log A+t leg D'rt.+t log D~x+log C'Ji"-P) ... (7)In the present case P = 0, and to evaluate A, thevalue of E; was obtained from the intercept on theordinate of the plot_[E+2.3RT.lOg_ i _] vs i/id (ref. 10, 11)nF td-lKoryta treatment12 - This was also modified similarto the Gellings treatment. (k~)B was evaluated usingEq. (8)kG) _ i' v'D'rt. DMX c/3n{ e B - C=-'--'-. .'- 886 ! xId-21' o· twhere i' is the current when E = Eli The value-of E! is obtained by drawing an assymptot of thelog plot from the region E-++oo. The potentialat which this asymptote cuts the abscissa is E~'Stability constants of complexes - The stabilityconstant (log K) of each complex was determinedusing the method giv~n by Lingane'", taking s~riesof ligand concentratIOns. The values are gIvenin Table 2.The structure" of the ligands suggest that thestability of Bi-ST should be greater than the othertwo complexes as ST (Ib) has -OR group in t~e. ringat ortho position which may form an. additionalcoordinate bond with the central metal ion. Suchpossibility is not seen ~th other l.iga~ds. Theexperimental results obtame~ .<l:reqUl!e III agree-ment with this fact. The stabilities are III the order:Bi-ST>Bi-VT~Bi-BT.For all the three complexes, the reduction of thecomplex is slower than that of the metal ion. The•.• (8)1052reduction rate increases with temperature (Table 1).Thermodynamic functions of electrode reaction(Table 3) support this fact. Higher the stabilityof the complex, lower is the reduction rate. As freeenergy change is positive it can be predicted thatthe. re~ction IS not spontaneous and requiresactivation energy.The complexation is less favoured at higher tem-peratures as the stability constants decrease with risein temperature. Negative free energy change alsodecreases with the increase in temperature. Thevalues of /).S are nearly constant and negative, asmust be the case with neutral Iigands-",Comparison of the three treatments - The valuesof (ke)B obtained with the three different treatmentsare in good agreement, though the values obtainedby Koryta treatment show slight variations. ThisTABLE 1- POLAROGRAPHIC BEHAVIOUR OF Bi(III) SCHIFFBASE COMPLEXES[Ligand]M0·000·0250'0350-050o-co0'0290-0400·0450-0240'0450·060-Ei(vs SCE)Gellings Koryta MatsudaBi-BT3442503442500·1930·1880·1860-2090·2020-2000·2130·2060·2040·2180·2100'20839·047·054·03'34·46·24·55·97·55·57·08·658·060·062·03-64·86'65'76·98·35·97·58·959·071·097·01·93·15·60·71'32·40·30·71·70·91·92'50·71·62·01·12·32·756·058·060·0H4·16·34·55·97·35·67·08·762·074·093·02·32·95·30·91·62-90·41·01·91·32·13·10·61·73·01·51·83·73442503442SOBi-ST3442500·1580'1570·15659·074·099·03442500'211 2·20·197 2'80·184 5·00·216 0·80·200 1'30·190 2'60·218 0'30·201 0'70·191 1·8Bi-VT0'178 1·10·170 1·90·166 3·10·184 1-10·174 1-60·170 2·70·192 1-10·180 1·90·174 2·73442503442503442503442SO344250PATEL et al.: POLAROGRAPHIC STUDY OF COMPLEXATION OF Bis, WITH SCHIFF BASESTABLE 2 - STABILITY CONSTANTS AND THERMODYNAMICFUNCTIONSTemp.(0C)log K l!.G l!.Hkcal kcalmole"! mole"!Bi-BT2·34 -3·322-22 -3,23 -5·0342-15 -3-20l!.Se.u,344250-5·62344250Bi-ST4'2 -5·963·5 -5·102·9 -4,33Bi-VT2·53 -3'512'20 -3·172·05 -2·96-32·6-37·5 -102-8344250-13,5TABLE 3 - THERMODYNAMIC FUNCTIONS OF ELECTRODEREACTION FOR Bi- VT[Ligand]M0·00Temp.(0C)344250344250l!.Gkcal mole-!l!.Hkcal mole-!+5·024+5·016+5·008+5'17+5·13+5·08+5-4920·045may be due to the fact that the equation employedin Koryta treatment utilizes the value of i'lid -2i'which has less accuracy compared to the formermethods.In order to evaluate log A in Gellings treatmentE; was obtained by extrapolation method10'1l, whilein Matsuda treatment E. was obtained by calculationand hence it seems to be more accurate.AcknowledgementThe authors thank Prof. K. A. Thaker for labora-tory facilities, and the CSIR, New Delhi, for theaward of junior research fellowships to two of them(M.S.P. and T.T.).References1. NAZAROV, B. F., TRUKHACHEV'A, V. A. & STROMBERG,A. G., Izv. uyssh, ucheb. Zaued, Khim. Technol., 15(1972), 983; Chem. Abstr., 77 (1972),0171904s.2. CHlKRYZOV'A, E. G. & MERYAN, V. T., Zh. analit. Khim.,22 (1972), 1542.3. SUNDARESAN, R. & SUNDARAM, A. K., Proc. Indian Acad,sa: 78 (1973). 225.4. RUSTAGI, S. C. & RAO, G. N., Indian]. Chem., 13 (1975),702.5. HEINERT, D. & MARTELL, A. :8., J. Am. chem. Soc., 84-(1962), 3257.6. MATSUDA, H. & AYABE, Y., Z. Elektrochem., 63 (1959),1164.7. DELAHAY, P., J. Am. chem. Soc., 75 (1953), 1430.8. GELLlNGS, P. J., Z. Elekirochem., 66 (1962), 477.9. MEITES, L., Polarographic technique (Interscience Pub-lishers, New York). 1967, 251.10. VERMA, P. S., JAIN, D. S. & GAUR, J. N., Indian J.Chem., 13 (1975), 586.11. CHANDRASEKHARAN, V. R., SUNDARESAN, R., SARAIYA,S. C. & RADHAKRISHNAN, T. P., Study of irreversibleprocesses by polarography [Bhabha Atomic ResearchCentre, Bombay), 1968, 10.12. KORYTA, J., Electrochim. Acta, 6 (1962), 67.13. LINGANE, J. J., Chern. Rev., 29 (1941), 1.14. PERRIN, D. D., Organic complexing reagents (IntersciencePublishers, New York), 1964, 49.1053

Polarographic Study of Complexation of BP+ with Schiff Bases In Acetate Buffer

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Polarographic Study of Complexation of BP+ with Schiff Bases In Acetate Buffer

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