Ion pairing in tetraphenylporphyrin oxidation: A semiquantitative study

Haoran Sun, Justin C. Biffinger, Stephen G. DiMagno

Research output: Contribution to journalArticle

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Abstract

In 1,2-difluorobenzene (DFB), electrolyte conductivity measurements and cyclic voltammetric titration on the traditional benchmark tetraphenylporphyrin, H2tpp, permit the first estimate of ion pair association constants for singly- and doubly-oxidized free-base porphyrins. From ion titration cyclic voltammetry and digital simulation, measured association constants for H 2tpp+X- were 65, 120, 210, 520 and 730 M -1, for X- = PF6-, ClO 4-, NTf2-, BF4 - and OTf-, respectively, relative to the association constant for the H2tpp+TFPB- complex. By similar methods it was found that the association constants for the corresponding dication, H2tpp2+, were at least 3.0 × 104 M-1 (PF6-), 2.5 × 10 6 M-1 (ClO4-), 5.2 × 10 5 M-1 (NTf2-), 1.9 × 10 6 M-1 (BF4-) and 2.7 × 10 6 M-1 (OTf-). We demonstrate that differences in association constants allow the formal potential of the second oxidation of H2tpp to be shifted by more than 800 mV simply by varying the solvent and electrolyte. In addition, calculated electrostatic potential energy maps for porphyrin dications suggest that exposure of the core N - H groups is responsible for the change in ordering of anion affinities that occurs upon oxidation of H2tpp+.

Original languageEnglish (US)
Pages (from-to)3148-3154
Number of pages7
JournalDalton Transactions
Issue number19
DOIs
StatePublished - Oct 7 2005

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Association reactions
Ions
Oxidation
Porphyrins
Titration
Electrolytes
Potential energy
Cyclic voltammetry
Anions
Electrostatics
tetraphenylporphyrin

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Ion pairing in tetraphenylporphyrin oxidation : A semiquantitative study. / Sun, Haoran; Biffinger, Justin C.; DiMagno, Stephen G.

In: Dalton Transactions, No. 19, 07.10.2005, p. 3148-3154.

Research output: Contribution to journalArticle

Sun, Haoran ; Biffinger, Justin C. ; DiMagno, Stephen G. / Ion pairing in tetraphenylporphyrin oxidation : A semiquantitative study. In: Dalton Transactions. 2005 ; No. 19. pp. 3148-3154.
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