EDTA to check the purity of solid C6H5TI(III) salts, and to standardize their aqueous stock solutions even at a high ionic strength. It is noteworthy that the absorption spectrum of the aqueous 4.7) corresponds to the system Tl(1)-xylenol orange (at pH ligand spectrum, so that no complex formation seems to take place. It follows that only C6HsT1(III)and Tl(III), between the thallium acceptors investigated during this work, form a complex with xylenol orange. This may be explained by ( 5 ) and taking into account the acid character of CBH~TI(III) of Tl(II1) in aqueous solution (6). The reported complex formation between CsHsTI(II1) and both the ligands investigated enlarges the knowledge of the coordination chemistry of organometallic cations. Very little is known about C6H5TI(III),and C6H5T1-(oxinate)lis the only chelate complex hitherto studied (1, 4, 7,8); on the other
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(5) G . Faraglia, L. Roncucci Fiorani, B. L. Pepe, and R. Barbieri, Itiorg. Nucl. Chem. Letters, 2,277 (1966). (6) L. G. Sillen and A. E. Martell, “Stability Constants of Metal Ion Complexes,’’ Special Publ. No. 17, Chem. SOC.,London, 1964.
hand, the only information concerning organometal-EDTA complexes consists of the preparation of some Rz Sn(1V) and R2Pb(IV) derivatives (9, IO). We recently succeeded in the preparation of the solid C6HsTl-EDTA, simply by crystallization from an aqueous solution containing 1 :1 C6H5TIC12and EDTA (2 moles of NaCl per mole of complex remained in the solution phase). We intend to continue our work also on organometal-EDTA complexes, with the aim of investigating the metal atom coordination number and the structure of the complexes. RECEIVED for review September 5 , 1967. Accepted October 26, 1967. Investigation supported by NATO Research Grant No. 301. (7) G. Faraglia, L. Roncucci, and R. Barbieri, Ric. Sci., 35(IIA), 205 (1965). (8) D. Seyferth and R. Bruce King, “Annual Surveys of Organometallic Chemistry,” Vol. 1-2, Elsevier, Amsterdam, 1965-66. (9) H. G . Langer, U. S. Patent 3,117,147, Jan. 7, 1964; Chem. Absrr., 60, 8061d(1964). (10) H. G. Langer, U. S. Patent 3,120,550, Feb. 4, 1964; Chem. Abstr., 60, 120516 (1964).
Spectrophotometric Determination of PaIladium with 2,2’- Dipyridyl ketoxime William J. Holland and John Bozic Depariinent of Chemistry, University of Windsor, Windsor, Ontario, Canada
IN A previous communication ( I ) , the use of pyridine ketoximes in the determination of palladium, gold, rhenium, and iron was summarized. The purpose of the present work was to show that a symmetrical pyridine ketoxime in which no possibility of syn and anti forms exists could be used in the determination of palladium. The fact that such isomers cannot exist for this ligand makes possible a reasonable structural assignment for the resulting complex. The platinum group metals do not interfere and microgram quantities of gold can be tolerated. Interferences due to iron, cobalt, nickel, and copper can be eliminated by the use of ethylenediamine tetraacetic acid disodium salt. Palladium reacts with the reagent to form a water insoluble chelate which is extractable into chloroform. The result of palladium analysis of the chelate showed that the palladium and the reagent combined in the ratio of 1 mole to 2 moles. The palladium chelate in chloroform exhibits an absorption maximum at 410 mp and has a molar absorptivity of 1.2 X 104. EXPERIMENTAL
Instruments. Spectral studies were made with a Hitachi Perkin Elmer Spectrophotometer, a Beckman DB Spectrophotometer, and a Beckman DK-1A Recording Spectrophotometer using 1-cm matched silica cells. Infrared spectra were obtained with the Beckman IR-10 Spectrophotometer. Measurements of pH were made with a Corning Model 12 pH meter. (1) W. J. Holland and J. Bozic, ANAL.CHEM., 39, 109 (1967).
Preparation of Reagent. The procedure of Henze and Knowles (2) may be employed to synthesize 2,2’-dipyridylketone. The starting ketone is also commercially available from The Aldrich Chemical Co., Milwaukee, Wis. The ketone was converted to the oxime with hydroxylamine hydrochloride and after several recrystallizations from water melted at 141-142.5’ C. Anal. calculated for CllH90N3: C, 66.32%; H, 4.55%. Found: C, 66.20%; H, 4.62z. Carbon and hydrogen analyses were done by the Spang Microanalytical Laboratory, Ann Arbor, Mich. Reagent Solution. A 1 % solution of the reagent in 95 ethanol was used. The solution was stable for several months. Standard Solutions. The standard palladium solution was prepared by dissolving anhydrous palladium(I1) chloride in concentrated hydrochloric acid, diluting to 1 liter with distilled water and standardizing by the dimethylglyoxime method according to Vogel (3). Solutions of diverse cations were prepared from their chlorides or nitrates and solutions of diverse anions from their sodium or potassium salts. Procedure. An aliquot of solution containing approximately 20 to 200 pg of palladium(I1) was transferred to a 60-ml separatory funnel. The contents were made slightly acidic by addition of a few drops of dilute hydrochloric acid or potassium hydroxide. To this solution was added 4 ml of a 0.2N sodium acetate-0.2N acetic acid buffer of pH 4.5 and the volume made up to approximately 15-20 ml with distilled water. Two milliliters of reagent solution was added and the contents were shaken briefly. The yellow (2) H. R. Henze and M. B. Knowles, J . Org. Chem., 19, 1127 (1954). (3) A. I. Vogel, “A Textbook of Quantitative Analysis,” 3rd Ed., Longmans Canada Ltd., Toronto, Canada, 1961, p. 512. VOL 40, NO. 2, FEBRUARY 1968
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Experiment 1 2 3 a
Table I. Precision and Accuracyo Std. Rei. dev., Palladium, PPm Taken Found error ppm 1.60 4.00 6.40
1.60 4.00 6.41
0.00 0.00 0.16
0.01 0.01 0.03
Range, PPm 0.03 0.04 0.10
Each result is the average of nine separate analyses.
Table 11. Infrared Absorption Bands (cm-l) Pyridine ring Compound C = N N-0 1 2 3 1569 1477 985 1600 HPAO 1520 1567 1473 1598 1550 998 HDPK 1482 1605 1561 1505 1175 Pd(PA0)z 1469 1586 1561 1172 Pd(DPK)z 1495
4 1439 1434 1424 1435
HPAO-2-p yridinealdoxime.
HDPK-2,2'-dipyridylketoxime. Pd(PAO)z-palladium 2-pyridine aldoxime. Pd(DPK)z-palladium 2,2'-dipyridylketoxime.
precipitate was allowed to develop for 10 to 15 minutes and extracted twice with 7- to 8-ml portions of chloroform into 25-ml glass stoppered graduated cylinders, The funnel stem contained a small plug of glass wool. The combined washings and extract were diluted to volume with chloroform. A blank was prepared in a similar manner, The absorbance of the chloroform extract was measured at 410 mp and the amount of palladium was calculated from a previously prepared calibration curve. No palladium was found remaining in the aqueous layer on applying the p-nitrosodiphenylamine spot test. RESULTS
Influence of pH on Complex Formation and Extraction. The optimum pH range for complex formation and extraction was 4 to 5 employing a 0.2N sodium acetate-0.2N acetic acid buffer. Effect of Reagent and Temperature. There was no change in absorbance when five times the required amount of reagent was added. Variation in temperature between 20" and 40" did not significantly affect the absorbance readings-i.e., within 1-2z. Effect of Time. Chelate formation was complete in 6 to 7 minutes. There was no change in absorbance of the chloroform extract after two weeks of standing. Effect of Solvent. At a pH of 4 to 5 , the water insoluble chelate was completely extracted into benzene, chloroform, dichloromethane; partially extracted into carbon tetrachloride, isoamyl alcohol, nitrobenzene, bromobenzene, ethyl acetate, toluene, xylene, and not extracted into diethyl ether, hexane, or pentane. Beer's Law. A straight line was obtained over the range 0.5-10 ppm when absorbance was plotted against concentration. The optimum concentration range evaluated by Ringbom's method ( 4 , 5 ) was 3.5-8 ppm. Precision and Accuracy. The precision and accuracy of the method was studied by analyzing solutions containing known amounts of palladium using the outlined procedure. The results are summarized in Table I. (4) G. H. Ayres, ANAL.CHEM., 21,652 (1949). (5) A. Ringbom, 2.Anal. Chem., 115, 332 (1938).
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0
ANALYTICAL CHEMISTRY
Effect of Diverse Ions. Five milligrams of a diverse ion was added to a separatory funnel containing 100 pg of palladium and the extraction was performed according to the outlined procedure. The following ions did not interfere: Na+, K+, Mg+z, Ca+z, Srf2, Zn+z, Mn+2, Crf3, CT~O,-~, Pb+z, Al-3, Ba+2, T1+, Bif3, Te+', UOzcZ, Hgt2, Ag+, NO3-, clod-, C1-, F-, I-, Br-, NH4+,Re+', P P 2 , PtC4,Ost4, Rh+3, R u + ~ Ir+2. , The presence of hydroxylamine hydrochloride ensured the lower oxidation states of ruthenium and iridium. The formation of AgCl did not interfere because it was trapped in the glass wool plug. The system could also tolerate large amounts of common masking agents such as EDTA, citrate ion, acetate ion, and tartrate ion. The following ions did not interfere when used in conjunction with the corresponding masking agents: 5 mg of C U + ~N, P 2 , Fe+z,and C O +masked ~ with 3 ml of 0.1MEDTA solution; 5 mg of V t 2 masked with 4 ml of 0.1MEDTA after prior reduction with hydroxylamine hydrochloride in acid media; 5 mg of Be+2masked with 100 mg of sodium citrate; 5 mg of W04+ masked with 50 mg of F-; 5 mg of Zr-4 or Hff4masked with 300 mg of F-. Up to 100 pg of gold was tolerated without interference. CN- ion interfered severely and must be absent. Composition and Structure of the Palladium Chelate. The solid complex was isolated and dried for one hour at 110" C. Anal. calculated for Pd(CnHsN30)~: C, 52.55%; H, 3.21 %; Pd, 21.16%. Found: C, 52.60%; H, 3.33%; Pd, 21.27%. The infrared spectrum of the complex was examined and assignments were made for the four pyridine ring bands, the C=N vibration frequency and the N-0 stretching mode. The assignments agree favorably with those proposed by Krause, Colthup, and Busch (6) for the palladium chelate of 2-pyridinealdoxime a closely related compound containing the -C=N-0 group. Table I1 compares the assignments for these analogous compounds. The table comparisons indicate that the palladium is bound to the nitrogen of the nitrone group rather than to the oxygen. Powell (7-9) has reported weak bands near 500 cm-1 in palladium amine complexes, all of which he assigned to the palladium-nitrogen stretching frequency. In a study of the infrared spectrum of the palladium 2,2'-dipyridylketoxime complex a weak band was observed at 515 cm-'. Molecular models of the palladium 2,2'-dipyridylketoxime complex indicate that a trans configuration is more sterically favorable than a cis configuration. From the above evidence a reasonable structure for the chelate is as follows :
RECEIVED for review July 31, 1967. Accepted November 20, 1967. Work supported by the National Research Council of Canada and a Province of Ontario Fellowship. ~~
(6) R. A. Krause, N. B. Colthup, and D. H. Busch, J. Phys. Chem., 65,2216 (1961). (7) D. B. Powell, Chem. Eng. (London), 1956,313. (8) D. B. Powell and N. Sheppard, J. Chem. Soc., 1956, 3108. (9) D. B. Powell, Zbid.,p. 4495.
