Joseph, P. T.

Mohandas, P. N.

Pavithran, C.

Warrier, K. G. K.

English

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INDIAN J. CHEM., VOL. 14A, JULY 19767. TSUKAMATO,T., Chem, A bstr. , 55 (1961), 5879f.8· JOB, P., Ann. Chim., 6 (1936), 97.9. SUBBARAMARAo, K. V. & RAGHAVRAO,B. H. S. V.,J. scient. indo Res., 14B (1955). 278.10. CALVIN, M. & WILSON. K. W .• J. Am. chem. Soc., 67(1954), 2003.11. BJERRUM, J., Metal aminine formation in aqueous solution(Haase, Copenhagen), 1941.12. IRVING, H. & ROSSOTTI,H. 5., J. chem, Soc., (1954).2904.13. IRVING; H. & ROSSOTTI,H. 5., J. chem. Soc .• (1953).3397.14. IRVING,H. & WILLIAMS,R. J. P., Nature, 162 (1948),746.Stepwise Formation Constants of La(III),Ce(III), Pr(III) & Nd(III) with 4-H'ydroxy-3-formyl-(2' /4')-methylazobenzenesK. G. K. WARRIER, C. PAVITHRAN,P. N. MOHANDAS &P. T. JOSEPHIndustrial Research Laboratory, Trivandrum 19Received 17 June 1975; accepted 4 October 1975Stepwise formation constants of La(III), Ce(III),Pr(III) and Nd(III) complexes with 4-hydroxy-3-formyl-(2'/4')-methylazobenzenes (HF2MB andHF4MB) have been determined in 60% aq, ethanol(w/w) at 28±O·P under Nt atmosphere, usln~ theCalvln-BJernim pH titration technique. The orderof formation constants of the complexes is Nd(UI)>Pr(III) >Ce(III)>La(III).SYNTHESIS and chelating tendencies of somesubstituted azo benzenes have been reportedby Mohan Das et al,l-s. The formation constantsof La(III), Ce(III). Pr(III) and Nd(III) complexeswith 4-hydroxy-3-formyl-(2' /4')-methylazobcnzenes(HF2MB and HF4MB) have now been determinedin 60% aq. ethanol (w/w) employing Bjerrum-Calvinpotentiometric titration technique.All the reagents were of AR grade (BDH). Pre-paration of ligands and details of experimentaldrocedure have been reported earlier-. Metal nitrate(La, Ce, Pr or Nd) solutions were prepared in con-ductivity water. Corrections in PH values weremade according to the method of Bates+, Themetal hydroxides precipitated at PH 7·30 and 7·50for Nd(III), 7·55 and 7·60 for Pr(III). 7·65 and 7,70for Ce(III) and 7·80 and 7·85 for La(III) in the caseof HF2MB and HF4MB complexes respectively.Despite the tendency of the complexes of these metalions to hydrolyse, such effects were ignored in thepresent study, since the complexes are stable inthe pH range studie~. . .All the ligands being mo.noprohc, neutrah~e o~eequivalent of the bas~ to gIve one bu!fer region l!lthe titration curves 10 accordance WIth the equi-librium (1).HA~H+ +A- ... (1)The acid dissociation constants of HF2MB andHF4MB were found to be 8·05 and 8·02 respectivelyby the methods of Irving and Rossetti- and Bjerrum.The formation curves for the metal-ligand systemswere drawn between ii and PA, the values of whichwere calculated according to the method of Bjerrumand Calvin", The complex equilibria may be re-presented by Eqs. (2-4).HA+Ms+=MA2++H+ (2)MA2++HA=MA~+H+ (3)MA~+HA=MA3+H+ (4)The log k values for these systems. wer~ obtainedfrom the formation curves and are given 10 Table 1along with probable errors. Refined values of log ~were also calculated by the correction-term methodand are given in Table 1. HF2MB and HF4MB behaveas bidentate ligands forming 1: 3 compl?xes. Theorder of stability of the metal complexes IS: Nd(III)>Pr(III»Ce(III»La(III) (Table 1). La(III).Ce(III), Pr(III) and Nd(III) have ionic radii of1·061 1·034 1·013 and 0·995 A respectively. Sincethe stability of the complexes of th.e m~tal ionshaving similar electronic configuration 1Ocreas~swith decreasing ionic size, the above order of stab~-lities is in accordance with the expected trend. ThISis also justified by considering Z2/r values for thesemetal ions.The order of ligands according to their chelatingtendency is HF2MB>HF4MB.References1. MOHAN DAS, P. N., SUNAR, O. P. & TRIVEDI, C. P.,Indian J. Chem., 11 (1973), 196.2. JOSEPH, P. T., THOMAS, O. F., IBRAHIM RAWTHER &MOHAN DAS, P. N., Indian J. Chem. (in press).3. MOHANDAS, P. N., SUNAR, O. P. & TRIVEDI, C. P., J.inorg, nucl, Chem., 35 (1973), 849.4. BATES, R. G., PAABO, M. & ROBINSON, R. A., J. Phys.Chem.,67 (1963), 1833.5. IRVING, H. & ROSSOTTI, H. 5., J. chem. s«; (1954),2904.6. CALVIN, M. & WILSON, L. W., J. Am. chem. s«.. 67(1945), 2003.TABLE 1 - STEPWISE FORMATIONCONSTANTSOF VARIOUSMETALCOMPLEXESOBTAINEDBY BJERRUM-CALVINMETHODMetal ion HF2MB HF4MBlog k, log kl log k. log (3. log k, log k. log k. log (3.Nd(III) 5·64 4·31 3-70 13-65 5·22 3-97 3·60 12·79(13·57) (12·69)Pr(III) 5·22 3·92 3·55 12·69 5·10 3·92 3·50 12·52(12-80) (12·62)Ce(III) 5·27 3·86 3·47 12-60 4·97 4·88 3·47 12·32(12'20) (12·50)La(IiI) 5·06 3·70 3·37 12-13 4·65 3·60 3·35 11·60(12'15) (11·31)Values in parentheses have been obtained by correction-term method.540

Stepwise Formation Constants of La(III), Ce(III), Pr(III) & Nd(III) with 4-H'ydroxy- 3-formyl-(2'/4')-methylazobenzenes

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Stepwise Formation Constants of La(III), Ce(III), Pr(III) & Nd(III) with 4-H'ydroxy- 3-formyl-(2'/4')-methylazobenzenes

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