NOTES

For the complex A.en [Found: Ti, 15·26; Cl, 22·74;S, 10·48;. F, 6,28; C, 11·45; H, 3,75; N, 9·53.Reqd.: Tl, 15·53; CI, 22·97; S, 10,35; F, 6·15; C,11·55; H, 3·56; N, 9·05%]. For the complex

A.DMSO [Found: Ti, 14·89; Cl, 21-32; S, 20·08;F, 5·96; C, 10·60; H, 2·85. Reqd.: Ti, 14·67; Cl,21?0; ~, 19·57; F, 5,81; C, 11:00; H, 2·75%].

Tltamum, sulphur and fluonne were determined,gravimetrically 2S Ti02, BaS04 and (C6HslaSnFrespectively. Chlorine was determined by Volha.rd'smethod. The parent compound and its coordination,complexes are yellow, hygroscopic solids, insoluble in,common organic solventS. Their melting points are>260°.

It is now well established that the symmetry()f the fluorosulphate group is reduced from Cav(when it is ionic) to Cs when it acts as a mono- orbidentate groupa-5. However, if it acts as a tri­<Ientate ligard its symmetry still remains Cav. Thislowering of the symmetry (when it acts as amOl1O- or bidentate ligand) results in an incre2seof its fundamental vibrations from six to nine,all of which are IiR and Raman active. The IRabsorption bands for the fluorosulphate group in (A)>can be assigned on the basis of Cav symmetrywhich is maintained not because of the anionicSOaF-, but due to the metal-anion coordination,in which all the three oxygen atoms of the fluoro­sulphate group are involved in coordination in anequivalent position resulting in hexa-coordination oftitanium. That the fluorosulphate group in (A) isnot ionic becomes evident from a comparison of itsIR spectra (',1max in em-I) with that of CsSOaF(ref. 6). The ',12mode shows a significant shift from715 in the cesium salt to 820. There is consistent,though smaller, shift in VI and Va modes (VI shiftsfrom 1078 to 1090, while Vashifts from 558 to 580).'.14' ',Is and ',16modes appear at 1230, 560 and 420respectively. There is, thus, a probability that theiluorosulphate group in (A) is tridentate having aCav symmetry.

The presence of the methoxy group in (A) issupported by its analytical data as well as by itsIR spectrum. The IR spectrum of (A) as a mullin hexachlorobutadiene shows bands at 2920 and2885, which may be attributed to vC-H. Otherbands usually attributed to an alkoxy group arealso present in (A) and also in its coordination>complexes under discussion. In pure methanol, thebands at 1035-65 are attributed to vO-C; whilein Ti(OCHa)Cla these bands are found at a lowerposition; i.e. 980-1000. The bands at 975-1025indicate the presence of OCHa group in (A).

The splitting of all the three E modes, in thecoordination complexes of (A) indicate the reducedsymmetry (C5) of the fluorosulphate group. Theyappear at 1340, 1260 (\14) and 680, 588 (\15) inA.Py, at 1370, 1310 (',14),656, 579 (\15)& 420, 370(\16)in A.en and at 1370, 1260 (\14), 655, 579 (',Is)

& 435, 345 (\16) in A.DMSO respec~ively .. -r:heformation of 1:1 complexes of (A) WIth pyndmeand dimethyl sulphoxide suggest that the fluoro­sulphate group behaves .as a :nonodentate c~valentliga~d and that titann~m .IS penta-coor~ma~ed.In 'the case of ethylenedlamme complex, tltanmmseems to acquire hexa-coordination. In pure liquid

pyridine the 16b vibrations (out-of-plane ring de­formation) appears at 403, while the 6a and 8bvibrations (in-plane ring deformation) appear at601 and 1578 respectively'. These vibrations inTiCI2(OCHa) (SOaF).Py show significant shift to higherregion and appear at 419,624 and 1600 respectively,indicating the coordination of pyridine to themetal. The prominent bands at 3505 (\IN-·H)

and ~655 (N -H bending) in ethylenediamine8 shiftto 3445 and 1600 respectively in the complexTiCI2(OCHa)(SOaF).eIl. The vC~N band appearingat 1225 in the pure base shows no significantchange. The trend in the shift of the N - Hfrequencies indicates that titanium is coordinated toethylenediamine and has acquired hexa-coordination.Pure dimethyl sulphoxide shows two characteristicbands 'at 1050 and 690 assigned to vS=O and\lC-S respectively9. The vS=O in the complexTiCI2(OCHa)(SOaF).DMSO appears at 990. The lower­ing of this frequency indicates the coordination ofdimethyl sulphoxide to titanium through its oxygenatom, since the coordination through sulphur atomwould have increased the \lS=O as is knownin its complexes with platinum and palladium(II)halidesIo,ll. The upward shift in the vC-S to 720further justifies the suggested mode of coordination.References

1. FRAZER, M. J., GERRARD, W. & PARRETT, F. \V., J.chem. Soc., (1965), 3687.

2. BEERMAN;C. & BESTIAN, R., Angew. Chem., 71 (1959), 618.3. GOUBEAU, R. & MILNE, J. B., Can. J. Chem., 45 (1967),

2322.4. YEATS, P. A., POH, B. L. FORD, B. F. E., SAMS, J. R. &

AUBKE, F., J. chem. Soc. (A), (1970), 2188.5. CARTER, R. A., JONES, S. P. L. & AUBKE, F., Inorg.

Chem., 9 (1970), 2485.6. RUOFF, A., MILNE, J. B•• KAUFMANN, G. & LEROY, M.,

Z. anorg. allg. Chem., 372 (1970), 119.7. GILL, N. S., NUTTALL, R. H., SCAIFE, D. E. & SHARP,

D. W. A., ]. inorg. nucl. Chem., 18 (1961), 79.8. NAKAMOTO, K., Infrared spectra of inorganic and co­

ordination compounds (Wiley Interscience, New York),1970, 224.

9. LAPPERT, M. F. & SMITH, J. K., J. chem. Soc., (1961), 3224.10. COTTON, F. A. & FRANCIS, R.o J. Am. chem. Soc., 82

(1960), 2986.11. COTTON, F. A., FRANCIS, R. & HORROCKS (Jr), W. D.,

J. phys. Chem., 64 (1960), 1534.

Stability Constants of Co(II), Ni(II), Cu(II),Zn(II), Cd(II), UO~+ & V02+ Chelates ofo-(N -a,-furfuralideneimino )benzoic Acid

D. C. SEHGAL, P. K. KANUNGO & R. K. i\'IEHTA

Department of Chemistry, University of Jodhpur, Jodhpur

Received 16 APril 1977; accepted 18 July 1977

Stability constants of Co(II), Ni(II) , Cu(II), Zn(II),Cd(II), UO~+ and V02+ complexes with o-(N-o.-fur­furalideneimino)benzoic acid have been determinedpotentiometrically in aqueous media using Calvin­Bjerrum pH titration technique. The measurementshave been carried out at three different ionic strengthsand temperatures. Thermodynamic stability con­stants have been obtained by extrapolating the experi­mental values to zero ionic stren~th. Values of freeenergy change have also been calculated.

175

INDIAN J. CHEM., VOL. 16A, FEBRUARY 19711

A SURVEYl-3 of the literature indicated thatno work has been done on Co(II), Ni(Il),

Cu(Il), Zn(Il), Cd(Il), UO~+ and V02+ chelates ofo-(N-ot-furfuralideneimino)benzoic acid (HFB) , theSchiff base derived from furfur aldehyde and anthra­nilic acid. Hence the present work on the potentio­metric studies of these chelates was undertaken.The measurements were carried out using Calvin­Bjerrum pH-titration technique4 at 25°, 30° and35° in aqueous media ([1. = O'lM, 0'05M and O'OlMNaCl04)·

The apparatus and the reagents employed werethe same as reported5 earlier. HFB was synthesizedby the general procedure already reported5.

For Ithe evaluation of the stability constants,experiments were carried out in media of low ionicstrengths (O'lM, 0'05M and O·OlM). From thevalues obtained, an extrapolation to the zero ionicstrength was carried out. The following mixtures(total volume 40·0 ml) were titrated against standardcarbonate-free sodium hydroxide (O·lM). The titra­tion curves had the usual shapes. (i) 10·0 ml ofO·OlM HFB+4·0 ml of 1·0M NaCl04+26·0 mlof water, (ii) 10·0 ml of O'OlM HFB+4'0 ml of1·0M NaCl04+10·0 ml of O'OlM metal ion solution+16·0 ml of water, (iii) 20·0 ml of O·OlM HFB+

10·0 ml of O'OlM metal ion solution +4·0 ml of1,OM NaCl04+6:0 ml of water.

The stability constants of the bivalent chelates.at different ionic strengths and temperatures aregiven in Table 1. As indicated by the formationcurves, the n value is more than 1·5 in the cases.of V02+, UO~+, Cu(Il), Ni(Il) and Co(II) chelates.suggesting the formation of 1: 2 complexes. Thevalue of n is less than 1for Zn(Il) and Cd(II),chelates which suggests the formation of 1:1 com­plexes in these cases. The stabilities of the metalchelates follow the order, V02+> UO~+>Cu(Il»Ni(Il»Co(II»Zn(II»Cd(II), which.is in accord-ance with the Irving-Williams rule6• ~

The thermodynamic stability constants were ob-·tained by extrapolation of the experimentally obtain­ed stability constants to zero ionic strength in the;piots between log of stability constant and v~­where [1. is the ionic strength. The values ofthermodynamic stability constants thus obtained forV02+, UO~+,Cu(II), Ni(Il), Co(II), Zn(Il) and Cd(II}chelates are, respectively, 8·63, 8'02, 7'70, 7,15,7·00, 3,49 and 3·31 at 25°; 8·75, 8,20, 7'80, 7·48,7'10, 3·55 and 3·37 at 30°; and 9·00, 8·28, 7,90,7,60, 7,25, 3·65 and 3,45 at 35°. The values of-!:ll' (in kcalfmole) for these chelates at 25°, 300-

Ti\:BLE 1 - DISSOCIATIONCONSTANTSOF .HFB AND STABILITY CONSTANTSOF IITS BIVALENT METAL CHELATESAT DIFFERENT IONIC STRENGTHS

Dissociation/stability

25°30°35°constants

-----------O·lM

O'OSMO'OlMO'lMO'OSMO·OlMO·OlM0·05MO·OlM

HFBlog K~

6·106'256'356·026·156'305·956·056·20-

V02+ log Kl

4'434,564'724,464·624,764,484,704,8';1log K2

3,593-653'703-663'703'803,723-803-88

UO~+ log Kl

4'324,364'404,374'454,504·414'524'60log K2

3'263,353'453·293,403'503'323,453'55-

Cu(II) log Kl

4·264·304,354'284'354'404'294,404·45-log K2

3·173·203'253'203'253'293'233'303'35-

Ni(II) log Kl

3,843'873,903,883-954·023-924·024·1o.log K.

3·093'103·173·123'203'293,133-273-3<)

Co (II) log Kl

3,683·703,803'743-803-853,803·903-99>log K.

3,033·053'103,043'083·123·043·103'12'

Zn(II} log Kl

3-223'3030403'283'3530493'3330453'55

Cd (II) log Kl

3·073·153'253·143-223·323'203'303040

176

.and 35° respectively are, V02+ (11'76, 12'14, 12·69);UO~+ (10'92, 11·37, 11·67); Cu(II) (10,50, 10·79,11-14); Ni(II) (9'75, 10'37, 10·71); Co(II) (9'54,'9'84, 10·22); Zn(II) (4'75, 4'92, 5·14) and Cd (II)(4'51, 4'67, 4·86).

The data were analysed in terms of theHarned's? relation between log Kf and temperature[(PKH-ct2)=-2c6t+(PK~-c62)J. The values of'e and PK~ for HFB were found to be 188° and4·78 respectively. /iH values as calculated fromHarned's equation were found to be 6'624, 6·637and 6·643 at 298°, 303° and 308°K respectively.

References1. COTTON, F. A., Prog, inorg. cu«; 7 (1966), 88..2. HODGSON, D. J., Prog. inorg . Chem., 19 (1975), 1.3. SYAMAL, A., Coord. chem, Reu., 16 (1975), 309.

-4. BJERRUM, J., Metal ammine formation in aqueous solution(P. Hasse & Sons, Copenhagen). 1941.

5. MEHTA, R. K. & GUPTA, R. K., Indian J. cu,«, 11(1973), 56.

<6. IRVING, H. & WILLIAMS, R. J. P., Nature, 162 \1948),746; J. chem, Soc., (1953), 3192.

7. HARNED, H. S. & KAZANJIAN, J. Am. chem, Soc., 58(1936), 1912.

Spectrophotometric Determination ofUranium(VI) with Thiobenzoyltrifluoroacetone

G. N. RAO & V. S. CHOUHAN

Chemistry Department, Indian Institute of Technology~C\V Delhi 110029

Received 18 February 1977; revised 20 August 1977accepted 24 September 1977

Thiobenzoyltrifluoroacetone (SBTA) has been usedfor the extraction and spectrophotometric determina-tion of uranium(VI). Quantitative extraction of theyellow uranium(VI) complex has been carried out inthe pH range 6·8-7·0. Absorbance of the complex was-measured at 375 nm. Interference due to a number-of cations and anions has also been studied.

THIOTHENOYLTRIFLUOROACETONE (STTA)has been used for spectrophotometric determina-

tion of several metals=". Compared to thenoyl-trifluoroacetone its thio derivative forms moreintensely coloured chelates with several transitionmetal ions-, Benzoyltrifluoroacetone (BT A) has beenused for the extraction and spectrophotometricdetermination of Cu(II), Ni(II), Co(II)5,6 and U(VI)7.In this paper extraction and spectrophotometric-deterrnina tion of uranium(VI) with thiobenzoyl-trifluoroacetone is described.

Spectrophotometric measurements were performedon Bausch Lomb spectronic-20 spectrophotometerand Unicam SP-500 spectrophotometer. For PHmeasurements Elico pH-meter was used. Thio-benzoyltrifluoroacetone was prepared starting fro inbenzoyltrifluoroacetone (Fluka reagent grade), follow-ing the method of Berg and Reed+ with somemodifications. Its purity was established by micro-analysis and molecular weight determination (freez-ing point method). Visible and infrared spectra

NOTES

provided further checks on its purity. Stock solutionof uranium(VI) was prepared from reagent gradeuranyl acetate and estimated by standard methods.Solutions of required concentrations for the extrac-tion experiments were obtained by suitable dilution.Buffer solutions of the required pH range wereprepared from mixtures of acetic acid and sodiumacetate and ammonia and ammonium chloride.

General procedure - An aliquot (5 ml) of uranium-(VI) solution was mixed with the huffer solution(5 ml) of desired pH value in a pyrex glass-stopperedbottle. Thiobenzoyltrifluoroacetone solution (10 ml,1 mM) in chloroform was added to this solutionand the contents were shaken on a wrist-actionflask shaker for different intervals of time. Afterallowing the two layers to settle the organic layerwas carefully separated employing a separatingfunnel and the absorbance of the yellow colouredcomplex was measured against the reagent blankat 375 nm.

Both the ligand and the metal complex absorbin the region 300-420 nm. Since the maximumdifference between the absorbance of the metalcomplex and the ligand occurs at 375 nm, thiswave length was adopted for further detailed work.From experiments carried out with buffers in thepH range 1-9 [uraniumfv I) = 160 {J-gj10ml, 10 mlof 1 mM SBTA in CHC13] it was found thatquantitative extraction of uranium(VI) occurs in thepH range 6·8-7·0:.,.,This was confirmed by checkingfor uranium(VI) in the aqueous phase. Differentamounts of uranium(VI) in the concentration range3 {J-gjml were extracted with 1 mM SBTA inCHCla' The plot of absorbance VE$SUS concentrationof uranium(VI) is linear passing through the origin,indicating that Beer's law is applicable under theseconditions. Molar absorptivity of the complex was9900 ± 200 and standard deviation was found to be1·6% in a set of ten measurements with 160 {J-gofuranium(VI). Experiments conducted with. differentuoncentrations of the ligand indicated that 10 ml of1 mM SBTA was sufficient for quantitative extrac-tion of uranium up to 250 {J-g. As the ligand alsoabsorbs at 375 nm, there is no advantage in usinga higher concentration of the ligand. Effect ofdiverse ions on the extraction of 160 {J-gof uranium(VI) with 10 ml of 1 mM SBTA in chloroform was,studied by adding the aqueous solutions of the \required salts. In presence of 2000 {J-gof ci,tr.a..:teand oxalgje the extraction was completely sup-presser Similar amounts of borate and fluorideinterfere in the estimation. However, there is nointerference from up to 2000 {J-g of Cl, Br,NO;; SO~-, Cd2+, Mn2+, T]3+, Mo+(VI), W+(VI),Ba2+, Ca2+, Na+, K+ or Mg2+. Ni2+, Zn2+, Cu2+,Pd2+, Fe3'\-, Ag+, Au3+, Pt4+, Pb2+ and Hg2+ aretolerated up to 200 {J-g. Thus, this method isaccurate, sensitive and useful for the determinationof uranium(VI) in microgram amounts.

The authors thank the CSIR, New Delhi, forfinancial support.References1. HONJYO, T. & KIBA, T., Bull. chem, Soc. Japan, 45

(1972), 185.2. SHINDE, V. M. & KHOPKAR, S. M., Anal. Chem., 41

(1969), 342.

177