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Kinetics and mechanism for reduction of trans-dichlorotetracyanoplatinate(IV) by tetraammineplatinum(II) and bis(ethylenediammine)platinum(II)

Shi, Tiesheng LU and Elding, Lars Ivar LU (1998) In Inorganica Chimica Acta 1998(282). p.55-60
Abstract
Reduction of trans-[Pt(CN)(4)Cl-2](2-) by [Pt(NH3)(4)](2+) and [Pt(en)(2)](2+) was studied at 25 degrees C in the range 0 less than or equal to [Cl-] less than or equal to 0.4 M by use of stopped-flow spectrophotometry. The stoichiometry [Pt(IV)]:[Pt(II)] is 1:1. Rapid-scan spectra show clear-cut isosbestic points, indicating that no reaction intermediates are accumulated to a significant amount. For pseudo first-order conditions with excess Pt(II), the observed rate constants can be expressed as k(obsd)=(k(1)+k(2)K[Cl-])[Pt(II)], with k(1)=400+/-10 and (3.3+/-0.4)x10(3)M(-1)s(-1), and k(2)K= (3.25 +/-0.04) X 10(4) and (6.67 +/-0.07) x 10(5) M-2 s(-1) at 25 degrees C for reduction by [Pt(NH3)(4)](2+) and [Pt(en)(2)](2+), respectively. The... (More)
Reduction of trans-[Pt(CN)(4)Cl-2](2-) by [Pt(NH3)(4)](2+) and [Pt(en)(2)](2+) was studied at 25 degrees C in the range 0 less than or equal to [Cl-] less than or equal to 0.4 M by use of stopped-flow spectrophotometry. The stoichiometry [Pt(IV)]:[Pt(II)] is 1:1. Rapid-scan spectra show clear-cut isosbestic points, indicating that no reaction intermediates are accumulated to a significant amount. For pseudo first-order conditions with excess Pt(II), the observed rate constants can be expressed as k(obsd)=(k(1)+k(2)K[Cl-])[Pt(II)], with k(1)=400+/-10 and (3.3+/-0.4)x10(3)M(-1)s(-1), and k(2)K= (3.25 +/-0.04) X 10(4) and (6.67 +/-0.07) x 10(5) M-2 s(-1) at 25 degrees C for reduction by [Pt(NH3)(4)](2+) and [Pt(en)(2)](2+), respectively. The mechanism involves two parallel reaction pathways. The analysis of the ionic strength dependence of k(1), together with the rapid-scan spectra, implies that reduction of trans-[Pt(CN)(4)Cl-2](2-) by these Pt(II) complexes takes place directly via chloride-bridged transition states of the type [H2O ... Pt-II... Cl ... Pt-IV... Cl](not equal) for the k(1) pathway, or [Cl ... Pt-II... Cl ... Pt-IV... Cl](not equal) for the k(2) path. The higher-reaction rate of [Pt(en)(2)](2+) compared with [Pt(NH3)(4)](2+) is due to a higher electron density in the d(z)2 orbital making it more readily available to accommodate the Cl+ leaving from the platinum(IV). The redox rates depend strongly on the thermodynamic driving force, reflecting a significant weakening of the Cl-Pt-IV bonds in the transition states. The much faster reduction of [Pt(CN)(4)Cl-2](2-) compared with Pt(IV) ammine complexes previously studied is rationalized in terms of transition state stabilization due to the strong sigma-donor and pi-acceptor properties of cyanide. (C) 1998 Elsevier Science S.A. All rights reserved. (Less)
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Contribution to journal
publication status
published
subject
keywords
Inorganic chemistry, Platinum(II) complexes, Ammine complexes, Cyano complexes, Kinetics, Reaction mechanism
in
Inorganica Chimica Acta
volume
1998
issue
282
pages
6 pages
publisher
Elsevier
ISSN
0020-1693
DOI
10.1016/S0020-1693(98)00199-6
language
English
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yes
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971dece4-36d6-45fd-85c5-3765ca763a39
date added to LUP
2016-12-18 18:38:44
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2017-03-20 21:14:10
@article{971dece4-36d6-45fd-85c5-3765ca763a39,
  abstract     = {Reduction of trans-[Pt(CN)(4)Cl-2](2-) by [Pt(NH3)(4)](2+) and [Pt(en)(2)](2+) was studied at 25 degrees C in the range 0 less than or equal to [Cl-] less than or equal to 0.4 M by use of stopped-flow spectrophotometry. The stoichiometry [Pt(IV)]:[Pt(II)] is 1:1. Rapid-scan spectra show clear-cut isosbestic points, indicating that no reaction intermediates are accumulated to a significant amount. For pseudo first-order conditions with excess Pt(II), the observed rate constants can be expressed as k(obsd)=(k(1)+k(2)K[Cl-])[Pt(II)], with k(1)=400+/-10 and (3.3+/-0.4)x10(3)M(-1)s(-1), and k(2)K= (3.25 +/-0.04) X 10(4) and (6.67 +/-0.07) x 10(5) M-2 s(-1) at 25 degrees C for reduction by [Pt(NH3)(4)](2+) and [Pt(en)(2)](2+), respectively. The mechanism involves two parallel reaction pathways. The analysis of the ionic strength dependence of k(1), together with the rapid-scan spectra, implies that reduction of trans-[Pt(CN)(4)Cl-2](2-) by these Pt(II) complexes takes place directly via chloride-bridged transition states of the type [H2O ... Pt-II... Cl ... Pt-IV... Cl](not equal) for the k(1) pathway, or [Cl ... Pt-II... Cl ... Pt-IV... Cl](not equal) for the k(2) path. The higher-reaction rate of [Pt(en)(2)](2+) compared with [Pt(NH3)(4)](2+) is due to a higher electron density in the d(z)2 orbital making it more readily available to accommodate the Cl+ leaving from the platinum(IV). The redox rates depend strongly on the thermodynamic driving force, reflecting a significant weakening of the Cl-Pt-IV bonds in the transition states. The much faster reduction of [Pt(CN)(4)Cl-2](2-) compared with Pt(IV) ammine complexes previously studied is rationalized in terms of transition state stabilization due to the strong sigma-donor and pi-acceptor properties of cyanide. (C) 1998 Elsevier Science S.A. All rights reserved.},
  author       = {Shi, Tiesheng and Elding, Lars Ivar},
  issn         = {0020-1693},
  keyword      = {Inorganic chemistry,Platinum(II) complexes,Ammine complexes,Cyano complexes,Kinetics,Reaction mechanism},
  language     = {eng},
  number       = {282},
  pages        = {55--60},
  publisher    = {Elsevier},
  series       = {Inorganica Chimica Acta},
  title        = {Kinetics and mechanism for reduction of trans-dichlorotetracyanoplatinate(IV) by tetraammineplatinum(II) and bis(ethylenediammine)platinum(II)},
  url          = {http://dx.doi.org/10.1016/S0020-1693(98)00199-6},
  volume       = {1998},
  year         = {1998},
}