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 J. Fraser Stoddart 10.1021/jacs.6b04343.s007 https://acs.figshare.com/articles/dataset/Influence_of_Constitution_and_Charge_on_Radical_Pairing_Interactions_in_Tris-radical_Tricationic_Complexes/3457628 The results of a systematic investigation of tris­radical tri­cationic complexes formed between cyclobis­(paraquat-<i>p</i>-phenylene) bis­radical dicationic (CBPQT<sup>2(•+)</sup>) rings and a series of 18 dumbbells, containing centrally located 4,4′-bipyridinium radical cationic (BIPY<sup>•+</sup>) units within oligo­methylene chains terminated for the most part by charged 3,5-dimethyl­pyridinium (PY<sup>+</sup>) and/or neutral 3,5-dimethyl­phenyl (PH) groups, are reported. The complexes were obtained by treating equimolar amounts of the CBPQT<sup>4+</sup> ring and the dumbbells containing BIPY<sup>2+</sup> units with zinc dust in acetonitrile 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 showed that the association constants (<i>K</i><sub>a</sub>) for complex formation vary over a wide range, from 800 M<sup>–1</sup> for the weakest to 180 000 M<sup>–1</sup> for the strongest. While Coulombic repulsions emanating from PY<sup>+</sup> 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<sup>•+</sup> units stand to gain some additional stabilization from C–H···π interactions between the CBPQT<sup>2(•+)</sup> rings and the PH termini on the dumbbells. The findings reported in this Article demonstrate how structural changes implemented remotely from the BIPY<sup>•+</sup> units influence their non-covalent bonding interactions with CBPQT<sup>2(•+)</sup> 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, 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. 2016-06-06 00:00:00 CBPQT dumbbell BIPY Coulombic repulsions Radical Pairing Interactions PY PH interaction UV tris complex DFT