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Charge-localized p-phenylenedihydrazine radical cations: ESR and optical studies of intramolecular electron transfer rates

Nelsen, Stephen F. and Ismagilov, Rustem F. and Powell, Douglas R. (1997) Charge-localized p-phenylenedihydrazine radical cations: ESR and optical studies of intramolecular electron transfer rates. Journal of the American Chemical Society, 119 (42). pp. 10213-10222. ISSN 0002-7863. doi:10.1021/ja9720321.

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1,4-Bis(2-tert-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl)benzene-1,4-diyl (2) its 2,5-dimethyl and 2,3,5,6-tetramethyl derivatives (3 and 4), their radical cations, and bis-radical dications are studied. Crystal structures including those of 2^+BPh_4^-, 3^(2+)(BPh_4^-)_2, 4^+BPh_4^-, and 4^(2+)(BPh_4^-)_2 establish that ring methylation causes more N-lone pair, aryl π twist without changing the NAr,NAr distance significantly and that both 2^+ and 4^+ have the charge localized in one hydrazine unit. NMR measurements show that 3^+ has about 6% of its spin at the four aryl CH and CMe carbons, while 4^+ has about 1.5% of its spin at the four CMe carbons. The average distance between the unpaired electrons of 3^(2+) and 4^(2+) was obtained from the dipolar splittings of their thermally excited triplet states and, as expected, is significantly smaller for 3^(2+) (5.25 Å) than for 4^(2+) (5.63 Å). Rate constants for electron transfer between the hydrazine units of 3^+ and 4^+ in CH_2Cl_2 and CH_3CN were determined by dynamic ESR. The intervalence radical cations show charge transfer bands corresponding to vertical electron transfer between the ground state and the highly vibrationally excited electron-shifted state, allowing calculation of the parameters controlling electron transfer. Electron transfer parameters obtained from the CT bands using adiabatic energy surfaces which approximate the CT band shapes observed produce rate constants within experimental error of those extrapolated to room temperature from the ESR data for both 3^+ and 4^+ in both solvents, without using tunneling corrections. The effects of mixing of the electronic wave functions of the reduced and oxidized hydrazine units of 2^+ on d_(NN), the C(t-Bu)N,NA(Ar) twist angle, and the aryl nitrogen lone pair, aryl π twist angle which are observed by X-ray are close to those predicted from the position of the minima on the ET coordinate X of the adiabatic energy surface calculated from the CT band.

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Ismagilov, Rustem F.0000-0002-3680-4399
Additional Information:Copyright © 1997 American Chemical Society. Published In Issue: October 22, 1997. Received June 19, 1997. We thank the National Science Foundation for support of this work under Grant CHE-9417946 and the major instrument program for funds used in purchase of the diffractometers, spectrometers, and computer equipment used. Supporting Information Available: Crystallographic data for 5^+(B(C_2H)_4^-, 3^(2+)BPh_4^-, 4^+BPh_4^-, and 4^(2+)(BPh_4^-_)2, numbered thermal ellipsoid drawings, and heavy atom positions (15 pages).
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Subject Keywords:splittings; complexes; ligand
Issue or Number:42
Record Number:CaltechAUTHORS:20130821-160727091
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40843
Deposited By: Whitney Barlow
Deposited On:29 Aug 2013 18:05
Last Modified:10 Nov 2021 00:09

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