INDIAN J. CHEM., VOL. 17A, JANUARY 1979 in a decrease of 'It-acceptor characteristics of the ligand which precludes the possibility of back-dona- tion. In the case of 2-methyl- and 4-methyl- pyridines (both having resonance), 'It-contributions are almost the same and the a-bonding is greater for 4-methylpyridine; as in case of 2-methylpyridine steric factor may come into play. So the stability constant values for lead (II) complexes with pyridine and methyl-substituted pyridines should follow the order viz. 3-methylpyridine < 2-m~thyl- pyridine < 4-methylpyridine < pyridine, same as observed in this investigation. References 1. ROSENTHAL, M. R. & DRAGO, R. S., Inorg. Chem., 4 (1965), 840. 2. PATEL, R. N. & RAMAN RAO, D. V., Indian]. Chem., 6 (1968), 112. 3. NELSON, S. M. & SHEPHERD, T. M., J. chem, Soc., (1965), 3276. 4. DESAI, A. G. & KABADI, M. B., J. Indian chem, Soc., 44 (1961), 532. 5. BJERRUM, J., Chem. Rev., 46 (1950), 381. 6. MUSGRAVE, T. R. & HUMBURG (Jr), E. R., J. inorg. nucl. Chem., 32 (1970), 2229. 7. PEARD, W. J. & PFLAUM, R. T., J. Am. chem, Soc., 80 (1958), 1593. 8. SUN, M. S. & BREWER, D. G., Can. J. Chem., 45 (1967), 2729. 9. MARTELL, A. E., in Stability constants of metal-ion complexes: SPecial Publication No. 17 (The Chemical Society, London), 1964, 440. 10. VAN UITERT, L. G. & HAss, C. G., J. Am. chem, Soc., 75 (1953), 451. Stability Constants of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) & Zn(II) with 1-(2-Quinolylazo)- 2-acenaphthylenol & 1-(2-Lepidylazo)-2- acenaphthylenol ISHWAR SINGH Sri Venkateswara College, New Delhi 110021 and B. S. GARG & R. P. SINGH* Department of Chemistry, University of Delhi Delhi 110007 Received 8 February 1978; accepted 19 June 1978 Dissociation constants of the two heterocyclic azo dyes, 1-(2-quinolylazo)-2-acenaphthylenol and 1-(2- lepidylazo)-2-acenaphthylenol, and the stability cons- tants of their complexes with bivalent metal ions have been determined pH-metrically, at 30 o ±1° in 75% dioxan medium and at different ionic strengths of NaClO,. Thermodynamic stabilization energies (0 H) of the complexes have been calculated using the method of George and McClure. F OR the spectrophotometric determination of many metal ions-+, 1-(2-quinolylazo)-2-acenaph- thylenol (QAAc) and 1-(2-1epidylazo)-2-acenaphthyl- enol (LAAc) have been used. The present note deals with the determination of dissociation constants of these dyes and formation constants of their com- plexes with bivalent transition metal ions. The stu- dies have been carried out in 75% dioxan medium 104 • at 30° + 1°. The formation constants of the metal- QAAc ~omplexes have been studied at different ionic strengths of sodium perchlorate and have been compared with the results obtained at ionic strength fl.=0·2 for metal-LAAc complexes. The thermodynamic stabilization energy ('~H) values have been calculated from log Kl values according to the method described by George and McClure 5 . A Beckman. pH-meter (expandomatic, SS-2 model) in conjunction with a glass electrode (0-14 PH range) and calomel electrode assembly, was used for pH-measurements. The PH meter was stan- dardized with potassium hydrogen phthalate and phosphate buffers. The calibration of PH meter reading was corrected in 3:1 dioxanjwater by titrat- ing 50 ml of 3:1 dioxanjwater at ionic strength (fl.) = 0·1 with standard perchloric acid. QAAc 6 and LAAc 4 were synthesized by methods described earlier. Solutions of these dyes were prepared in freshly distilled dioxan. All the metal ion solutions were prepared by dissolving the corres- ponding (AR quality) sulphates or nitrates and were standardized by well known methods. So- dium perchlorate (Riedel) was used to keep ionic strength constant. A 0·05 M solution of tetrame- thylammonium hydroxide (TMAH) (E. Merck, A.G., Darmstadt) in 75% dioxan (aqueous) was used as the titrant and this solution was standardized with a standard solution of oxalic acid. The dioxan used was purified by refluxing with sodium metal for 24 hr and was freshly distilled over sodium before use. All the other chemicals used were of reagent grade. All the measurements were carried out at 30° + 1°. Pre-saturated nitrogen (with 75% dioxan) -was passed through the solution during titrations. pH-titration procedure the experimental method of Bjerrum and Calvin, as modified by Irving and Rossotti", was used to determine the values of ii and pL. The following solutions (set I) were titrated against Mj20 TMAH solution in 75% dioxan for determination of stability constants of metal complexes at different ionic strengths. (i) 1·0 ml HCI0 4 (0·01M)+2·0 ml NaCl0 4 (2.0M) +1·0 ml KN0 3 or K 2 S0 4 (O·OlM) +1·0 ml H 2 0 +15·0 ml dioxan. (ii) 1·0 ml HCl0 4 (O·OlM) +2·0 ml NaCl0 4 (2.0M) +1·0 ml KN0 3 or K 2 S0 4 (0·01M)+1·0 ml H 2 0 +15 ml QAAc or LAAc (3'33x10- 3 M) in dioxan. (iii) 1·0 ml HCl0 4 (O·OlM) +2·0 ml NaCl0 4 (2,OM) + 1·0 ml metal nitrate or sulphate (O·OIM) + 1·0 ml H 2 0+15 ml QAAc (3·33 X 10-3M) in dioxan. In other sets, II, III and IV (studied only with QAAc) , requisite amount of NaCl0 4 was added to maintain ionic strength at 0·1, 0·01 and 0·005 M. In all the cases, corrections for change in volume on mixing dioxan and aqueous solution (total volume= 19·67 ml due to contraction on mixing dioxan and water) as well as changes in volume which take place during the course of titrations, were made. From the titration curves of acid alone and those obtained ~n ~he presence of ligand at a particular constant 1011lC strength, iiH values of the ligand (QAAc or LAAc) at various PH values were cal- culated and the PKNJ;I and PKOH values of the ligands were found by plotting log [(ii H -l)/(2-ii H )] versus pH and log [iiHj(l-ii H )] versus PH respectively.
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INDIAN J. CHEM., VOL. 17A, JANUARY 1979
in a decrease of 'It-acceptor characteristics of theligand which precludes the possibility of back-dona-tion. In the case of 2-methyl- and 4-methyl-pyridines (both having resonance), 'It-contributionsare almost the same and the a-bonding is greaterfor 4-methylpyridine; as in case of 2-methylpyridinesteric factor may come into play. So the stabilityconstant values for lead (II) complexes withpyridine and methyl-substituted pyridines shouldfollow the order viz. 3-methylpyridine < 2-m~thyl-pyridine < 4-methylpyridine < pyridine, sameas observed in this investigation.
References1. ROSENTHAL, M. R. & DRAGO, R. S., Inorg. Chem., 4
(1965), 840.2. PATEL, R. N. & RAMAN RAO, D. V., Indian]. Chem.,
6 (1968), 112.3. NELSON, S. M. & SHEPHERD, T. M., J. chem, Soc.,
(1965), 3276.4. DESAI, A. G. & KABADI, M. B., J. Indian chem, Soc.,
44 (1961), 532.5. BJERRUM, J., Chem. Rev., 46 (1950), 381.6. MUSGRAVE, T. R. & HUMBURG (Jr), E. R., J. inorg.
nucl. Chem., 32 (1970), 2229.7. PEARD, W. J. & PFLAUM, R. T., J. Am. chem, Soc., 80
(1958), 1593.8. SUN, M. S. & BREWER, D. G., Can. J. Chem., 45 (1967),
2729.9. MARTELL, A. E., in Stability constants of metal-ion
complexes: SPecial Publication No. 17 (The ChemicalSociety, London), 1964, 440.
10. VAN UITERT, L. G. & HAss, C. G., J. Am. chem, Soc.,75 (1953), 451.
Stability Constants of Mn(II), Fe(II), Co(II),Ni(II), Cu(II) & Zn(II) with 1-(2-Quinolylazo)-
2-acenaphthylenol & 1-(2-Lepidylazo)-2-acenaphthylenol
ISHWAR SINGHSri Venkateswara College, New Delhi 110021
andB. S. GARG & R. P. SINGH*
Department of Chemistry, University of DelhiDelhi 110007
Received 8 February 1978; accepted 19 June 1978
Dissociation constants of the two heterocyclic azodyes, 1-(2-quinolylazo)-2-acenaphthylenol and 1-(2-lepidylazo)-2-acenaphthylenol, and the stability cons-tants of their complexes with bivalent metal ions havebeen determined pH-metrically, at 30o±1° in 75%dioxan medium and at different ionic strengths ofNaClO,. Thermodynamic stabilization energies (0 H)of the complexes have been calculated using the methodof George and McClure.
FOR the spectrophotometric determination ofmany metal ions-+, 1-(2-quinolylazo)-2-acenaph-
thylenol (QAAc) and 1-(2-1epidylazo)-2-acenaphthyl-enol (LAAc) have been used. The present note dealswith the determination of dissociation constants ofthese dyes and formation constants of their com-plexes with bivalent transition metal ions. The stu-dies have been carried out in 75% dioxan medium
104•
I
at 30° + 1°. The formation constants of the metal-QAAc ~omplexes have been studied at differentionic strengths of sodium perchlorate and havebeen compared with the results obtained at ionicstrength fl.=0·2 for metal-LAAc complexes. Thethermodynamic stabilization energy ('~H) valueshave been calculated from log Kl values accordingto the method described by George and McClure5.
A Beckman. pH-meter (expandomatic, SS-2model) in conjunction with a glass electrode (0-14PH range) and calomel electrode assembly, was usedfor pH-measurements. The PH meter was stan-dardized with potassium hydrogen phthalate andphosphate buffers. The calibration of PH meterreading was corrected in 3:1 dioxanjwater by titrat-ing 50 ml of 3:1 dioxanjwater at ionic strength(fl.) = 0·1 with standard perchloric acid.
QAAc6 and LAAc4 were synthesized by methodsdescribed earlier. Solutions of these dyes wereprepared in freshly distilled dioxan. All the metalion solutions were prepared by dissolving the corres-ponding (AR quality) sulphates or nitrates andwere standardized by well known methods. So-dium perchlorate (Riedel) was used to keep ionicstrength constant. A 0·05 M solution of tetrame-thylammonium hydroxide (TMAH) (E. Merck, A.G.,Darmstadt) in 75% dioxan (aqueous) was usedas the titrant and this solution was standardizedwith a standard solution of oxalic acid. The dioxanused was purified by refluxing with sodium metal for24 hr and was freshly distilled over sodium before use.All the other chemicals used were of reagent grade.
All the measurements were carried out at 30° + 1°.Pre-saturated nitrogen (with 75% dioxan) -waspassed through the solution during titrations.
pH-titration procedure the experimental methodof Bjerrum and Calvin, as modified by Irving andRossotti", was used to determine the values of iiand pL. The following solutions (set I) weretitrated against Mj20 TMAH solution in 75% dioxanfor determination of stability constants of metalcomplexes at different ionic strengths.
(i) 1·0 ml HCI04 (0·01M)+2·0 ml NaCl04 (2.0M)+1·0 ml KN03 or K2S04 (O·OlM) +1·0 ml H20+15·0 ml dioxan.
(ii) 1·0 ml HCl04 (O·OlM) +2·0 ml NaCl04 (2.0M)+1·0 ml KN03 or K2S04 (0·01M)+1·0 ml H20+15 ml QAAc or LAAc (3'33x10-3M) in dioxan.
(iii) 1·0 ml HCl04 (O·OlM) +2·0 ml NaCl04 (2,OM)+ 1·0 ml metal nitrate or sulphate (O·OIM) +1·0 mlH20+15 ml QAAc (3·33 X 10-3M) in dioxan.
In other sets, II, III and IV (studied only withQAAc) , requisite amount of NaCl04 was added tomaintain ionic strength at 0·1, 0·01 and 0·005 M. Inall the cases, corrections for change in volume onmixing dioxan and aqueous solution (total volume=19·67 ml due to contraction on mixing dioxan andwater) as well as changes in volume which takeplace during the course of titrations, were made.
From the titration curves of acid alone and thoseobtained ~n ~he presence of ligand at a particularconstant 1011lC strength, iiH values of the ligand(QAAc or LAAc) at various PH values were cal-culated and the PKNJ;I and PKOH values of the ligandswere found by plotting log [(iiH-l)/(2-iiH)] versuspH and log [iiHj(l-iiH)] versus PH respectively.
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TABLE 1 - STABILITY CONSTANTS OF BIVALENT COMPLEXESOF QAAc AND LAAc AT DIFFERENT IONIC STRENGTHS
Cu (II) Fe(II) Zn(H) Ni(H) Co (II) Mn(H)
LAAc (iJ. = 6'2)log K, 9·12 8'85 7'59 7-40 7·30 6·36log K. 8·18 6·97 6·62 6'52 5·73~. 17·30 14·56 14'02 13-82 12'09
QAAc (iJ. = 0'2)log Kl 9'07 8'20 7·79 6·66 6·29 5·95log K. 7·43 6'72 6·17 5·85 5'52 5·10s, 16'50 14·92 13-96 12'51 11·81 11-05
QAAc (iJ. = 0·1)log K; 9·72 8'19 7-68 6·49 6·24 5·98log K. 8'68 7·41 7·12 6·11 6·02 5·88~. 18'40 15'60 14-80 12·60 12·26 11-86
QAAc (iJ. = 0'01)log Kl 10'62 8'70 8·24 7'37 6'74 6'40log K. 9·30 8·10 7·62 6·96 6·99 6·41~2 19·92 16·80 15'86 14·33 13·73 12·81
QAAc (iJ. = 0'005)log x, 11'20 9·85 9·87 9·18 7·88 8·00log K. 9·48 8·58 7·93 7·43 7'12 6·93(3. 20·68 18·43 17·80 16'61 15'00 14'93
TABLE 2 - STABILIZATION ENERGIES (II R) OF THE METALCOMPLEXES AT iJ. =: 0'2M (NaCI04)
Metal LAAc complexes QAAc complexesion
AG IIR AG 'ORkcal/mole (kcal/mole)
Mn(IJ) 8·67 8·11Fe(II) 12·06 19·0 11"18 19'0Co (II) 9·95 24·0 8·57 23·0Ni(II) 10·09 33-0 9'08 33'0Cu(II) 12·43 27'0 12·36 27'0Zn(lI) 10·35 10'62
From the titration curves of solutions (i), (ii)and (iii), ii values of the metal complexes weredetermined at various pH values. The formationcurves obtained by plotting the ii and pL valueshave been analysed for log KI and log K2, which aretabulated in Table 1.
Utilizing the values of stability constants, 6.Gand '8H functions have also been evaluated (Table 2).
The values of log KI and log K2 for the complexesof the metal ions studied are given in Table 1. Theorder of decreasing stability of the complexesformed by different metal ions is: Cu(II) > Fe(II)> Zn(II) > Ni(II) > Co (II) > Mn(II).
The above order of stabilities of the complexesis in agreement with the order reported by Irvingand Williams" and Mellor and Maley", except in thecase of Fe(II). This situation is observed in com-plexes of this metal ion with some other ligands10,1lalso. The stability constants of the metal complexesand PKOH values of the liaands at different ionicstrength show a regular and gradual increase withthe decrease of ionic strength of the medium. Theligand field stabilization energies ('8H) (Table 2) followthe order: Fe(II) < Co(II) < Ni(II) > Cu(II).
(
NOTES
References1. SINGH, ISHWAR, MEHTA, Y. L., GARG, B. S. & SINGH,
R. P., Talanta, 23 (1976), 617.2. SINGH, ISHWAR, GARG, B. S. & SINGH, R. P., Z. analyt,
cu-«, 284 (1977), 42.3. SINGH, ISHWAR, GARG, B. S. & SINGH, R. P., J. Indian
chem, s»; 54 (1977), 787.4. SINGH, ISHWAR, Ph.D. Thesis, University of Delhi, 1977.5. GEORGE, P. & MCCLURE, D. S., Progress in inorganic
chemistry, Vol. 1, edited by F. A. Cotton (Interscience,New York), 1959, 381.
6. MEHTA; Y. L., GARG, B. S. & SINGH, R. P., Curro Sci.,43 (1) (1974), 11.
7. IRVING, H. & ROSSOTTI, H., J. chem, so«, (1953), 3397.8. IRVING, H. & WILLIAMS, R. J. P., Nature, 162 (1948),746.9. MELLOR, D. P. & MALEY, L., Nature, 159 (1947), 370.
10. CALLAHAN, C. M., FERNELIUS, W. C. & BLOCK, B. P.,Analyt. chim, Acta, 16 (1957), tot.
11. BERGER, K., EGYED, I. & RUFF, I., J. inorg. nucl. Chem.,28 (1966), 139.
Spectroscopic Evidence for the Presence ofMono- &. Di-protonated Species of
p-N,N-DimethylaminobenzylideneaniIine & Itsp'-Substituted Derivatives
ALI A. H. SAEED
Chemistry Department, College of ScienceBasrah University, Basrah, Iraq
Received 19 March 1978; revised 3 July 1978;accepted 10 July 1978
The effects of solvent, substituent and protonationon the charge-transfer band ofp-N,N-dimethylamino-benzylldeneaniline and its p'-substituted derivativeshave been studied. In glacial acetic acid or dilutesulphuric acid these Schiff bases form a mono-proto-nated species, whereas in concentrated sulphuric acidthey form a diprotonated species. The monoproto-nated species have been isolated as red or orange solidsfrom dilute sulphuric acid medium.
THE electronic spectra of a number of azome-thines and related compounds have been studied
by several workers>", In the spectrum of P-N,N-dimethylaminobenzylideneaniline (I), two 7t*+-7ttransitions, a band at 360 nm and a shoulderaround 310 nm are observed. The former bandhas been attributed to a charge-transfer transitionan~ the latter to a transition involving a locallyexcited state (1B2u-type state of aniline-). Smetsand Delvaux? have reported that P-N,N-dimethy-laminobenzylideneaniline produces an intense bandin the acid media. Ricketts and Cho" interpretedthe spectral data in acid media and indicated thepresence of. ~ono-acid cations of benzylidene-p'-phenylazoaniline and P-N,N-dimethylaminobenzy-lidene-p'<phenylazoaniline resulting from protona-tion at the azo and the azomethine nitrogens.Molecular orbital calculationss predict that the monoprotonated species of the Schiff base (I) exists almostentirely in the anilinium form. In the present notethe ch~rge t~ansfer band in the spectrum of (I) hasbeen investigated further by studying both thesolver,tt a~d substitueD:t effects. The effect of pro-tonation IS also studied and compared with theprevious work6,9.
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