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 July 6, 2016 | Supplemental Material + Published
Journal Article Open

Influence of Constitution and Charge on Radical Pairing Interactions in Tris-radical Tricationic Complexes

Abstract

The results of a systematic investigation of trisradical tricationic complexes formed between cyclobis(paraquat-p-phenylene) bisradical dicationic (CBPQT2(•+)) rings and a series of 18 dumbbells, containing centrally located 4,4′-bipyridinium radical cationic (BIPY•+) units within oligomethylene chains terminated for the most part by charged 3,5-dimethylpyridinium (PY+) and/or neutral 3,5-dimethylphenyl (PH) groups, are reported. The complexes were obtained by treating equimolar amounts of the CBPQT4+ ring and the dumbbells containing BIPY2+ units with zinc dust in acetonitrile (MeCN) solutions. Whereas UV-VIS-NIR spectra revealed absorption bands centered on ca. 1100 nm with quite different intensities for the 1:1 complexes depending on the constitutions and charges on the dumbbells, titration experiments show that the association constants (Ka) for complex formation vary over a wide range from Ka values of 800 M^(-1) for the weakest to 180000 M^(-1) for the strongest. While Coulombic repulsions emanating from PY+ groups located at the ends of some of the dumbbells undoubtedly contribute to the destabilization of the trisradical tricationic complexes, solid-state superstructures support the contention that those dumbbells with neutral PH groups at the ends of flexible and appropriately constituted links to the BIPY•+ units stand to gain some additional stabilization from C‒H···π interactions between the CBPQT2(•+) rings and the PH termini on the dumbbells. The findings reported in this full paper demonstrate how structural changes implemented remotely from the BIPY•+ units influence their noncovalent bonding interactions with CBPQT2(•+) rings. Different secondary effects (Coulombic repulsions versus C‒H···π interactions) are uncovered and their contributions to both binding strengths associated with trisradical interactions and the kinetics of associations and dissociations are discussed at some length and are supported by extensive DFT calculations at the M06-D3 level. A fundamental understanding of molecular recognition in radical complexes has relevance when it comes to the design and synthesis of non-equilibrium systems.

Additional Information

© 2016 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: May 5, 2016; Published: June 6, 2016. This research is supported by National Science Foundation (NSF) under grant no. CHE-1308107. T.C., H.X., and W.A.G. thank the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award DESC0004993. This work was also supported by the NSF under grant no. CHE-1565925 (M.R.W.). The authors acknowledge the Integrated Molecular Structure Education and Research Center (IMSERC) at Northwestern University for NMR and HRMS characterizations. We thank Dr. Amy Sarjeant and Charlotte C. Stern for solving the single-crystal X-ray structures. C.C. thanks the Chinese Scholarship Council for the Award for Outstanding Self-Financed Students Abroad and Foresight Institute for the Distinguished Student Award. A.C.F. acknowledges support from the Earth-Life Science Institute. J.C.B. acknowledges postdoctoral support from the Howard Hughes Medical Institute through the Life Sciences Research Foundation.

Attached Files

Published - jacsCHENGet_al.pdf

Supplemental Material - ja6b04343_si_001.pdf

Supplemental Material - ja6b04343_si_002.cif

Supplemental Material - ja6b04343_si_003.cif

Supplemental Material - ja6b04343_si_004.cif

Supplemental Material - ja6b04343_si_005.cif

Supplemental Material - ja6b04343_si_006.cif

Supplemental Material - ja6b04343_si_007.cif

Files

jacsCHENGet_al.pdf
Files (17.6 MB)
Name Size Download all
md5:be1e4dddfae058bc4983c1ba232bb17c
684.3 kB Download
md5:e86e773c6f571601ffcb59f49f8f0c35
530.7 kB Download
md5:7ee6be5fe17158acc85383491a5a6fec
1.6 MB Download
md5:695f23ea3a0c0187097599bd8837111f
326.4 kB Download
md5:81321843eab50316aa69fd59455115a5
4.4 MB Preview Download
md5:b610e0d9cd235af5f19a01ca1acf1579
8.6 MB Preview Download
md5:e63fbbaf2aaa64d69decbadfa4cde481
219.9 kB Download
md5:1d2d9af3889bee6e388a15dfae0e2092
1.2 MB Download

Additional details

Created:
August 20, 2023
Modified:
October 18, 2023