NOTES
1 2 3 Moles 1,lO-phenanthroline/mole ferric ion. ig. l,-Molar ratio study: ( F e + + + ) = 2.5 X X = 400mp.
4
df,
be the dimer Fep(phen)nClswherein iron has the more cornmon coordination number of 6.
TABLE I RESULTSOF PRECIPITATE ANALYSIS Element
Found
Fe CI
16.2 30.5
[Fe(~hen)Clal, %
Calcd.
16.3 31 0
DEPARTMENT OF CHEMISTRY PURDUEUNIVERSITY LAFAYETTE, INDIANA
The Oxidation-Reduction Potentials of Systems Involving the Bivalent and Tervalent Complexes of Iron, Ruthenium and Osmium with 2,2’2 ”-Terpyridyl BY F. P. D ~ Y EARU D E. C. GYARFAS SEPTEMBER 16, 1953 RECEIVED
The bis-terpyridyl complexes of iron(III), ruthenium(II1) and osmium(II1) have not been prepared although the bivalent metal complexes have been known for some time,’ nor has the potential for the reaction M(trpy)2++G hl(trpy)2+++f ebeen determined save for the iron system, for which a single value, -1.10 + 0.01 v. in 0.1 f H2S04, is reported. The green ions M ( t r p y ) 2 + + +were found to be much less stable than the corresponding &I(dipy),+++ and rapid reduction occurred in solution except in the presence of a t least normal acid. At this acid concentration the iron(I1) compound was rapidly destroyed. b‘hilst the green crystalline perchlorates could be precipitated with sodium perchlorate after oxidation of the bivalent complexes with ceric nitrate, they underwent reduction (1) G T Morgan and F H Burstall, J Chcm SOL, 2 0 (1932). (2) 11’ 1%‘ Brdndt, THISJ O U R V A L 76, (1215 (1954)
Vol. 76
during filtration and washing. The complex osmium(II1) perchlorate, however, was isolated as a pure compound following oxidation with chlorine. The potentials of the iron and ruthenium systems were determined on solutions that had been exactly half oxidized with ceric ammonium sulfate. The potentials, developed on a smooth platinum electrode, rose rapidly on the addition of the oxidizing agent, and then fell a t a variable rate depending on the acid concentration. Since equilibrium is never attained on an electrode under such conditions, the maximum potential was taken as the oxidation-reduction potential, and no attempt was made to extrapolate to zero time. The potential of the osmium system was measured by allowing the electrode to reach equilibrium for 15-30 min. in an initially equimolar solution of the oxidant and reductant, immediately determining the oxidation-reduction ratio spectrophotometrically, and applying the usual correction. The dark brown Os1’ complex has a strong absorption maximum a t 490 m p and the green 0s1I1 complex has a high transmission in this region with an absorption maximum a t 630 mp. Using two 1-cni. cells placed in front of each other, one containing the oxidant with a trace of chlorine, the other with the pure reductant, and a 490 nip filter a calibration curve for various ratios WBS prepared. In the range 40-60ci‘, reductant this was a straight line and the oxidation-reduction ratio a t equilibrium could be readily ascertained. Although the color changes are favorable: Fe, violet to green; Ru, orange-red to green; Os dark brown to green, the instability of the oxidized form militates against the use of these compounds as oxidation-reduction indicators. Experimental Bis-2,2’,2”-terpyridylosmium(III) Perchlorate Dihydrate.-A warm aqueous solution of the bivalent complex iodide1 was treated with dilute perchloric acid and the resulting sparingly soluble perchlorate recrystallized from hot water. The finely divided microcrystalline powder w a a suspended in ice-water and oxidized by shaking in a current of chlorine. -4fter filtration from traces of unreacted material, the deep green solution was treated with a little 207, sodium perchlorate, the resulting green needles collected, washed with cold 2% perchloric acid, then purified ether containing a trace of chlorine and dried in vacuo. The dry substance was stable, but an aqueous solution a t pH 6 rapidly became brown due to reduction. This behavior is characteristic of the tervalent ion, ruthenium and osmiuni complexes with dipyridyl and phenanthroline.a .4n!ri. Calcd. for O ~ ( C ~ ~ € - T I I S ~ ) ~ (Oq, C ~19 ~ l!); ~)J.~H~~: K, 8.47. Found: Os, 19.3; S , 8.f;. Oxidation-Reduction Potentials.-The pure perchloratvs of the iron( 11) and ruthenium( 11) complexes1 in M/500 solution containing varlous concentrations of sulfuric acid were oxidized by the addition of the calculated volumc. of ,\~/100 ceric ammonium sulfate, prepared in sulfuric acid of the same concentration, in the oxidation-reduction assembly previously described.4 The potential of the saturated calomel half-cell, calibrated against the quinhydrone electrode a t pH 4 in the same assembly was taken as 0.2423 v . a t 25’. The oxidation-reduction mixture of thc osmium complexes was prepared initially M/2000 with respect t o each and 10-4.V with respect t o nitric acid, and subsequently diluted to M/4nOO with sulfuric acid. Higher (3) F.P. Dwyer and E. C. Gyarfas. ibid , 74, 4899 (1952). (4) G . T. Rarnss, P. P. Dwyer and E C. Gyarfas, Trux.< F ~ i v i r l c i y s v c . , 48, 269 (1952).
Dec. 20, 1934
NOTES
6321
concentrations could not be used owing t o the sparing solubility of the osmium( 11) complex. The potentials found are shown in Table I. The potentials are generally higher than with the corresponding dipyridyl complexes, which in 0.1 f acid, for comparison, are, respectively, - 1.07; -1.288: -0.856.'
Experimental.-The cis- and truns-[Co(en)zC12]C1 were prepared by the methods given by Bailar in "Inorganic Syntheses," Vol. 11. They were washed with alcohol followed by ether, dried a t l l O o , and stored in a desiccator. The 2methoxyethanol was Eastman Kodak Co. "Practical Grade." It was dried over anhydrous calcium sulfate and distilled into a dark glass stoppered bottle for storage. TABLE I Reagent grade KCl and KC104 were dried a t 110' and used without further treatment. The 2-methoxyethanol Acid concn., Fe(trpy)z++/ Ru(trpy)r +/ Os(trpy)z +/ f Fe(trpy)z+++,v. Ru(trpy)z+++,v. Os(trpy)z+++,v. solutions of these salts were prepared by shaking the solvent with the appropriate salt for about 10 hours a t room tem- 1.281" -0.9512* 0.1 - 1,076" perature and then filtering off the excess solid. These solu-1.263 -0,9414 0.2 -1.060 tions were analyzed by evaporating 5.00-ml. samples and 0 .5 - 1.054 -1,219 -0.9250 weighing the residue of salt. Solutions of the complex in the solvent were prepared by -1.202 - 0.9070 1 .o -0.927 mulling the salt with a small amount of liquid. The slurry 2.0 .... -1.175 -0.8838 was then filtered through a sintered glass filter and the concentrated solution was diluted to a convenient concentraf 0 . 0 0 2 v. tion. The usual volume of solution used was from 30 to 50 6 10.0002 v. ml. The concentration of the complex was determined The Standard Potential of the Os(trpy)z++/Os(trpyj2+++ colorimetrically a t 530 mp. The value of €530 in the equaSystem.-The potentials of oxidation-reduction mixture tion 0.D.530 = €510 X concn. (molar) X path length (cm.) above, with the addition of potassium nitrate were measured was found to be (83.0 + 1.6) O.D. units/millimole/cm.2 a t various ionic strengths a t 25". The plot of I'/2 against This was shown to be valid up to 0.01 Msolutions. Eh corrected, Table 11, gave a straight line of slope 16.6 Optical density was measured with a Beckman DU specmv./O.l unit of I'12. This compares with the calculated trophotometer. Samples were pipetted from a reaction Debye-Hiickel slope of 14.8 mv.* By extrapolation to I = flask in the constant temperature bath directly into a 1-cm. Corex cell and immediately measured. The time was re0, Eo was found to be -0.9866 =k 0.0005 v. as compared with corded a t the moment the sample was withdrawn from the the O~(dipy)~++/Os(dipy)3+++ system4 -0.8795 v. reaction flask. The entire operation took less than two minutes. TABLE TI The temperature in the constant temperature bath was I '/2 Eh E h (COT.) found to vary less than 3 ~ 0 . about 1 ~ the set temperature. -0.9773 -0.9786 Because of the subsequent reaction between the solvent 0.0474 and the trans-isomer the data could not be treated by the 0.0575 -0.9743 -0.9768 usual simple first order expression. Satisfactorily repro-0.9759 0.0652 -0,9726 ducible results were obtained by plotting the log O.D. 0,0791 -0.9682 -0.9734 against time and drawing a straight line through the initial points. I t was found that usually the first four or five 0.0908 - 0.9677 -0,9711 points, extending over almost all of the first half-life, were -0.9657 -0.9700 0.1013 fitted quite well by a straight line, from the slope of which ( 5 ) F. P. Dwyer and H. H. McKenzie, J. Proc. Roy. SOC.N. S. W., the rate constant was calculated. +
+
81,93 (1947). (6) F. P. Dwyer, ibid., 83, 134 (19L9). (7) F. P. Dwyer, N. H. Gibson and E. C . Gyarfas, ibid., 84, 80 (1950). (8) I. M , Kolthcff and W. J . Tomsicek. J . Phys. Cheni., 39, 945 (1935).
DEPARTMEST OF CHEMISTRY USIVERSITYOF SYDNEY SYDNEY, ACSTRALIA
Results.-The
of the complex, the chloride concentration, or the ionic strength of the solutions. This is shown in Table I. The evidence would seem to support an s N 1 mechanism for the isomerization.
The cis-trans Isomerization of [ C ~ ( e n ) ~ C l ~in] C l 2-Methoxyethanol BY R. F. TRIMBLE,J R . ~ RECEIVED JULY 27, 1954
rate constant for the reaction a t
50" is not dependent upon the initial concentration
TABLE I Concn. ( M ) of cis-c.
103
strength Ionic
kmin. X 108, -1
2.92" 3.52"
2.92 3.52 5.12 5.71 5.96 6.66 7.69 7.77 58.7 59.2 62.6 63.8 66.5 69.0 44.4 46.2 48.9
9.12 8.88 9.76 9.63 9.76 7.96 9.36 7.96 9.00 9.24 9.49 8.89 9.12 8.77 9.64 8.45 8.77
x
5.12" 5.71
Av.
(9.00 f 0.73)
In the course of some work with c i s - [ C ~ ( e n ) ~ C l ~ ] - 5.96" X lo-$ min.-1 6.66" C1 it was observed that a solution of the salt in 27.69" methoxyethanol changed in color from purple to 7.77" green. A study of the absorption spectra of the 1.59 solutions showed that the color change was due to 2.13 the rearrangement of the purple cis-isomer to the 5.53 (9.05 f 0.26) green trans-isomer. The kinetics of the reaction 6.69 X 10-3min.-l could be studied very easily with a spectrophotom9.38 eter a t 530 mp. The isomerization was found to be 11.9 followed by a slower reaction between the trans3.36 isomer and the solvent to give unknown products. An attempt was made to follow the reaction po(8.95 0.62) 5.23 larimetrically, but due to the high optical density 7.94 X lo-* min.-l of the cis-isomer a t the Nan wave length it was not a Duplicate runs. possible to obtain sufficiently large rotations for a kinetic study. The rate constant was determined a t four different temperatures from 30 to 50'. The results (1) Department of Chemistry, Southern Illinois University, Carbondale, Illinois. are summarized in Table 11.
