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

Cheng, Chuyang and Cheng, Tao and Xiao, Hai and Krzyaniak, Matthew D. and Wang, Yuping and McGonigal, Paul R. and Frasconi, Marco and Barnes, Jonathan C. and Fahrenbach, Albert C. and Wasielewski, Michael R. and Goddard, William A., III and Stoddart, J. Fraser (2016) Influence of Constitution and Charge on Radical Pairing Interactions in Tris-radical Tricationic Complexes. Journal of the American Chemical Society, 138 (26). pp. 8288-8300. ISSN 0002-7863. doi:10.1021/jacs.6b04343.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Cheng, Chuyang0000-0002-3834-0479
Cheng, Tao0000-0003-4830-177X
Xiao, Hai0000-0001-9399-1584
Krzyaniak, Matthew D.0000-0002-8761-7323
Wang, Yuping0000-0002-9315-2358
McGonigal, Paul R.0000-0002-8538-7579
Frasconi, Marco0000-0003-2010-175X
Wasielewski, Michael R.0000-0003-2920-5440
Goddard, William A., III0000-0003-0097-5716
Stoddart, J. Fraser0000-0003-3161-3697
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.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
Chinese Scholarship CouncilUNSPECIFIED
Foresight InstituteUNSPECIFIED
Earth-Life Science InstituteUNSPECIFIED
Howard Hughes Medical Institute (HHMI)UNSPECIFIED
Issue or Number:26
Record Number:CaltechAUTHORS:20160610-073334314
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Official Citation:Influence of Constitution and Charge on Radical Pairing Interactions in Tris-radical Tricationic Complexes Chuyang Cheng, Tao Cheng, Hai Xiao, Matthew D. Krzyaniak, Yuping Wang, Paul R. McGonigal, Marco Frasconi, Jonathan C. Barnes, Albert C. Fahrenbach, Michael R. Wasielewski, William A. Goddard III, and J. Fraser Stoddart Journal of the American Chemical Society 2016 138 (26), 8288-8300 DOI: 10.1021/jacs.6b04343
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67806
Deposited By: Ruth Sustaita
Deposited On:10 Jun 2016 18:48
Last Modified:11 Nov 2021 03:54

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