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The isokinetic relationship in reactions of ammine complexes
1206
Notes
3CJ-lsN, AIBrs,d(l): 8.00(I),6.70(3),5.50(I),4.00(I0),3.80(2),3.60(8),3.20(2),2.68(2),2.50(6),2-30(3), 2.23(2),2-18(I)2.00(I),I.87(2).
CsHsN, A I13,d(1):6-60( I),5-90(I),5-60(I),4.05(l0),3.80(I),3.60(I),3.50(I),3-40(8),3.35(4),3.25(4), 3.19(8),3.08(6),2-84(4),2-80(l),2.58(2),2.45(I),2.40(I),2.21(3),2.02(2),1-93(6),1.88(2). 3CsHsN, AII3,d(1):9.20(I),7.50(I),6.50(I),5.80(3),5-20(I),4.05(I0),3.95(8),3-75(4),3.40(I),3.15(2), 2.98( I),2.79(I),2.62(I),2.47(2),2.30(I),2.05(I),1.98(1),I.93( I),I.86( l). EXPERIMENTAL The complexes were prepared by methods already described[I, 4]. Capillary tubes were filledwith the powdered complexes in a dry-box. The powder photographs were taken by the Debye-Scherrer method using monochromatic copper-K a-radiation of wavelength 1.542 ~. We thank S.R.C. for a grant to J.W.W.
Chemistry Department The University Lancaster, England
J . W . WILSON I . J . WORRALL
4. J. W. Wilson and I. J. Worrall, J. chem. Soc, (A), 316 (1968). 5. A. K. Wick, Heir. chim,Acta, 51, 85 (1968).
J. inorg,nucl.Chem,,1969,Vol.31, pp. 1206to 1209. PergamonPress. Printedin Great Britain
The isokinetic relationship in reactions of ammine complexes (Received 16 March 1968) MANY kinetic investigations of reactions of transition-metal complexes with water and with hydroxide ion have been reported[l] and it may eventually be possible to correlate the observed kinetic parameters with properties of the central metal ion and ligands. However, even now there is no general agreement on the mechanisms involved[2]. It is often found in a series of organic reactions involving moderate changes in the structure of the reactants or solvents that the enthalpies and entropies of activation vary in the same direction; at times giving a linear relationship characteristic of a particular reaction series. This useful effect has been termed the iso-kinetic relationship[3], and it seems worthwhile to examine its application to inorganic reactions. Despite the amount of work which has been done on ammine systems surprisingly few data are suitable for this purpose but three attempts at correlation can be presented. Two examples are taken from the data now available on the reactions [ M ( N H z ) s X ] 2 + + O H - ~ [M(NHa)5OH]2÷+X -
(1)
1. For a recent compilation, see F, Basolo and R. G. Pearson, Mechanisms of Inorganic Reactions, 2nd Edn. Wiley, New York (1966). 2. R. D. Gillard, J. chem. Soc. (A), 917 (1967). 3. J. E. Le~er, J. org. Chem. 20, 1202 (1955); J. E. Leffier, J. org. Chem. 31, 533 (1966).
Notes
1207
where M = Co(Ill); X = C114], Br[5], 115], Na[6] and M = Rh(lll); X = C117], Br[7], I[7], N318]. The iso-kinetic plots for the pentammines are given in Fig. 1. The results are used in the form k = AeEA]RT. The small number of points do not allow firm conclusions to be drawn but the overall
o N3
34 ON 3 32
30
Br
28
l
l
18
20
22
Log A Fig. 1. Isokinetic relationships for cobalt(Ill) and rhodium(Ill) ammines.
pattern for Co(Ill) and Rh(lll) indicates that in both cases the azido-complex may react by a mechanism which differs from that of the halogeno-complexes. This duality of mechanism was suggested by Banerjea and Das Gupta[9] on the basis of the variation of activation energies for reaction (1) with ligand field strengths. In the light of the most recent data[4-6, 10,11] their diagram should be replaced by Fig. 2, which is very different, but still suggests two reaction mechanisms. The corresponding plot for Rh(lll) shown in Fig. 3 emphasises the similarities of the two systems. The other example, for which the data are presented in Fig. 4, is the aquation of trans-[Co(en)2Cl2] + studied in water and various water-solvent mixtures by Vasil'eva and Yatsimirskil[12]. Their data consists of thirteen points covering the range of activation energies 23-30kcal/mole and of log A, 13-4-17.6. The solvents are water, water-methanol, water-ethanol, water-acetone, and water-dioxane containing up to 60 per cent of the organic solvent but not a single point deviates significantly from the iso-kinetic plot. Although the authors concluded that their results support the presence of parellel SN1 and SN2 mechanisms and that the latter is favoured in the less aqueous media, the remarkable observed isokinetic relationship, over the wide range of values of A and EA, indicates that a single mechanism must be operative in all these solvent systems. In this event the insensitivity of mechanism to the solvent system would support the SN 1 dissociative mechanism.
4. 5. 6. 7. 8. 9. 10. 11. 12.
G. W. Bushnell and G. C. Lalor, J. inorg, nucl. Chem. 30, 219 (1968), S. C. Chan, K. Y. Hui, J. Miller and W. S. Tsang, J. chem. Soc. 3207 (1965). G. C. Lalor and E. A. Moelwyn-Hughes, J. chem. Soc. 1560 (1963). G . W . Bushnell, G. C. Lalor, and E. A. Moelwyn-Hughes,J. chem. Soc. (A), 719 (1966). C. S. Davis and G. C, Laior, J. chem. Soc.(A) In press. D. Banerjea and T. P, Das Gupta, J. inorg, nucl. Chem. 27, 2617 (1965), D. L. Gay a n d G . C. Laior, J. chem. Soc. (A), 1179 (1966). G. C. Laior and J. Lang, J. chem. Soc. 5620 (1963). V. N. Vasil'eva and K. B. Yatsimirskil, Russ. J. inorg. Chem. 7, 1307 (1962).
1208
Notes
11 NO 2
38
NCS 10
~. 34 ¢1 u .to
,.,.~
30
18000
I 20000 '9 (cm~)
I 22 000
Fig. 2. T h e variation of activation energy with the wave n u m b e r of the first ligand field band for the reactions [Co(N Ha)~V] 2+ + O H - ~ [Co(N H3)5OH]2+ + X - .
33L
O N3
32 o u
oBr 30
29
Cl 26 ( )00
I 30O0O
-~,(crn:t)
Fig. 3. T h e variation of activation energy with the wave n u m b e r of the first ligand field band for the reactions [Rh(N H:JsX] 2+ + O H - --* [Rh(NHa)~OH] 2+ + X - .
Notes
1209
3O
28
'"< 2e S $
2,* I
12
I
14
1(5
I
18
LogloA Fig. 4. The iso-kinetic relationship for the reaction trans- [Co(en)2CI=]~++H=O [Co(en)~CIH~O]z++CI- in various aqueous solvents as follows: (1) 60% methanol, (2) 60% dioxan, (3) 40% dioxan, (4) 39% methanol, (5) 60% acetone, (6) 54% ethanol, (7) 36% ethanol, (8) 40% acetone, (9) 18% ethanol, (10) 20% dioxan, (11) 20% methanol, (12) 20% acetone, (13) water.
Acknowledgement-The author thanks the donors of the Petroleum Research Fund administered by the American Chemical Society for support.
Chemistry Department University of the West Indies Mona, Kingston 7 Jamaica
G. C. LALOR
J. inorg, nucl. Chem., 1969, Vol. 3 I, pp. 1209 to 1212.
Pergamon Press.
Printed in Great Britain
V i b r a t i o n a l spectra of s o m e a d d u c t s o f t i n t e t r a i o d i d e (Received 9 May 1968) THe uSE of vibrational spectroscopy to assign the stereochemistry of 6-coordinate complexes has been well documented [ 1]. The examination of metal iodide adducts, however, has not been complete because of the lack of instruments capable of detecting metal-iodine vibrations. We report here the
I. I. R. Beattie, T. Giison, M. Webster and G. P. McQuillan, J. chem. Soc. 238 (1964); and references therein.
Notes
3CJ-lsN, AIBrs,d(l): 8.00(I),6.70(3),5.50(I),4.00(I0),3.80(2),3.60(8),3.20(2),2.68(2),2.50(6),2-30(3), 2.23(2),2-18(I)2.00(I),I.87(2).
CsHsN, A I13,d(1):6-60( I),5-90(I),5-60(I),4.05(l0),3.80(I),3.60(I),3.50(I),3-40(8),3.35(4),3.25(4), 3.19(8),3.08(6),2-84(4),2-80(l),2.58(2),2.45(I),2.40(I),2.21(3),2.02(2),1-93(6),1.88(2). 3CsHsN, AII3,d(1):9.20(I),7.50(I),6.50(I),5.80(3),5-20(I),4.05(I0),3.95(8),3-75(4),3.40(I),3.15(2), 2.98( I),2.79(I),2.62(I),2.47(2),2.30(I),2.05(I),1.98(1),I.93( I),I.86( l). EXPERIMENTAL The complexes were prepared by methods already described[I, 4]. Capillary tubes were filledwith the powdered complexes in a dry-box. The powder photographs were taken by the Debye-Scherrer method using monochromatic copper-K a-radiation of wavelength 1.542 ~. We thank S.R.C. for a grant to J.W.W.
Chemistry Department The University Lancaster, England
J . W . WILSON I . J . WORRALL
4. J. W. Wilson and I. J. Worrall, J. chem. Soc, (A), 316 (1968). 5. A. K. Wick, Heir. chim,Acta, 51, 85 (1968).
J. inorg,nucl.Chem,,1969,Vol.31, pp. 1206to 1209. PergamonPress. Printedin Great Britain
The isokinetic relationship in reactions of ammine complexes (Received 16 March 1968) MANY kinetic investigations of reactions of transition-metal complexes with water and with hydroxide ion have been reported[l] and it may eventually be possible to correlate the observed kinetic parameters with properties of the central metal ion and ligands. However, even now there is no general agreement on the mechanisms involved[2]. It is often found in a series of organic reactions involving moderate changes in the structure of the reactants or solvents that the enthalpies and entropies of activation vary in the same direction; at times giving a linear relationship characteristic of a particular reaction series. This useful effect has been termed the iso-kinetic relationship[3], and it seems worthwhile to examine its application to inorganic reactions. Despite the amount of work which has been done on ammine systems surprisingly few data are suitable for this purpose but three attempts at correlation can be presented. Two examples are taken from the data now available on the reactions [ M ( N H z ) s X ] 2 + + O H - ~ [M(NHa)5OH]2÷+X -
(1)
1. For a recent compilation, see F, Basolo and R. G. Pearson, Mechanisms of Inorganic Reactions, 2nd Edn. Wiley, New York (1966). 2. R. D. Gillard, J. chem. Soc. (A), 917 (1967). 3. J. E. Le~er, J. org. Chem. 20, 1202 (1955); J. E. Leffier, J. org. Chem. 31, 533 (1966).
Notes
1207
where M = Co(Ill); X = C114], Br[5], 115], Na[6] and M = Rh(lll); X = C117], Br[7], I[7], N318]. The iso-kinetic plots for the pentammines are given in Fig. 1. The results are used in the form k = AeEA]RT. The small number of points do not allow firm conclusions to be drawn but the overall
o N3
34 ON 3 32
30
Br
28
l
l
18
20
22
Log A Fig. 1. Isokinetic relationships for cobalt(Ill) and rhodium(Ill) ammines.
pattern for Co(Ill) and Rh(lll) indicates that in both cases the azido-complex may react by a mechanism which differs from that of the halogeno-complexes. This duality of mechanism was suggested by Banerjea and Das Gupta[9] on the basis of the variation of activation energies for reaction (1) with ligand field strengths. In the light of the most recent data[4-6, 10,11] their diagram should be replaced by Fig. 2, which is very different, but still suggests two reaction mechanisms. The corresponding plot for Rh(lll) shown in Fig. 3 emphasises the similarities of the two systems. The other example, for which the data are presented in Fig. 4, is the aquation of trans-[Co(en)2Cl2] + studied in water and various water-solvent mixtures by Vasil'eva and Yatsimirskil[12]. Their data consists of thirteen points covering the range of activation energies 23-30kcal/mole and of log A, 13-4-17.6. The solvents are water, water-methanol, water-ethanol, water-acetone, and water-dioxane containing up to 60 per cent of the organic solvent but not a single point deviates significantly from the iso-kinetic plot. Although the authors concluded that their results support the presence of parellel SN1 and SN2 mechanisms and that the latter is favoured in the less aqueous media, the remarkable observed isokinetic relationship, over the wide range of values of A and EA, indicates that a single mechanism must be operative in all these solvent systems. In this event the insensitivity of mechanism to the solvent system would support the SN 1 dissociative mechanism.
4. 5. 6. 7. 8. 9. 10. 11. 12.
G. W. Bushnell and G. C. Lalor, J. inorg, nucl. Chem. 30, 219 (1968), S. C. Chan, K. Y. Hui, J. Miller and W. S. Tsang, J. chem. Soc. 3207 (1965). G. C. Lalor and E. A. Moelwyn-Hughes, J. chem. Soc. 1560 (1963). G . W . Bushnell, G. C. Lalor, and E. A. Moelwyn-Hughes,J. chem. Soc. (A), 719 (1966). C. S. Davis and G. C, Laior, J. chem. Soc.(A) In press. D. Banerjea and T. P, Das Gupta, J. inorg, nucl. Chem. 27, 2617 (1965), D. L. Gay a n d G . C. Laior, J. chem. Soc. (A), 1179 (1966). G. C. Laior and J. Lang, J. chem. Soc. 5620 (1963). V. N. Vasil'eva and K. B. Yatsimirskil, Russ. J. inorg. Chem. 7, 1307 (1962).
1208
Notes
11 NO 2
38
NCS 10
~. 34 ¢1 u .to
,.,.~
30
18000
I 20000 '9 (cm~)
I 22 000
Fig. 2. T h e variation of activation energy with the wave n u m b e r of the first ligand field band for the reactions [Co(N Ha)~V] 2+ + O H - ~ [Co(N H3)5OH]2+ + X - .
33L
O N3
32 o u
oBr 30
29
Cl 26 ( )00
I 30O0O
-~,(crn:t)
Fig. 3. T h e variation of activation energy with the wave n u m b e r of the first ligand field band for the reactions [Rh(N H:JsX] 2+ + O H - --* [Rh(NHa)~OH] 2+ + X - .
Notes
1209
3O
28
'"< 2e S $
2,* I
12
I
14
1(5
I
18
LogloA Fig. 4. The iso-kinetic relationship for the reaction trans- [Co(en)2CI=]~++H=O [Co(en)~CIH~O]z++CI- in various aqueous solvents as follows: (1) 60% methanol, (2) 60% dioxan, (3) 40% dioxan, (4) 39% methanol, (5) 60% acetone, (6) 54% ethanol, (7) 36% ethanol, (8) 40% acetone, (9) 18% ethanol, (10) 20% dioxan, (11) 20% methanol, (12) 20% acetone, (13) water.
Acknowledgement-The author thanks the donors of the Petroleum Research Fund administered by the American Chemical Society for support.
Chemistry Department University of the West Indies Mona, Kingston 7 Jamaica
G. C. LALOR
J. inorg, nucl. Chem., 1969, Vol. 3 I, pp. 1209 to 1212.
Pergamon Press.
Printed in Great Britain
V i b r a t i o n a l spectra of s o m e a d d u c t s o f t i n t e t r a i o d i d e (Received 9 May 1968) THe uSE of vibrational spectroscopy to assign the stereochemistry of 6-coordinate complexes has been well documented [ 1]. The examination of metal iodide adducts, however, has not been complete because of the lack of instruments capable of detecting metal-iodine vibrations. We report here the
I. I. R. Beattie, T. Giison, M. Webster and G. P. McQuillan, J. chem. Soc. 238 (1964); and references therein.