Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published October 22, 1997 | Supplemental Material
Journal Article Open

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

Abstract

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.

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).

Attached Files

Supplemental Material - ja10213.cif

Supplemental Material - ja10213.pdf

Files

ja10213.pdf
Files (560.3 kB)
Name Size Download all
md5:4fcb93e6b525c93f03f06cd169476b6d
112.2 kB Download
md5:021cf578282a171232434b7db823a701
448.1 kB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023