Spin-Frustrated Trisradical Trication of PrismCage

Han Han; Yuheng Huang; Chun Tang; Yiming Liu; Matthew D Krzyaniak; Bo Song; Xuesong Li; Guangcheng Wu; Yong Wu; Ruihua Zhang; Yang Jiao; Xingang Zhao; Xiao-Yang Chen; Huang Wu; Charlotte L Stern; Yuguo Ma; Yunyan Qiu; Michael R Wasielewski; J Fraser Stoddart

doi:10.1021/jacs.3c04340

Spin-Frustrated Trisradical Trication of PrismCage

J Am Chem Soc. 2023 Aug 23;145(33):18402-18413. doi: 10.1021/jacs.3c04340. Epub 2023 Aug 14.

Authors

Han Han¹, Yuheng Huang^{1

2

3}, Chun Tang¹, Yiming Liu⁴, Matthew D Krzyaniak^{1

2

3}, Bo Song¹, Xuesong Li¹, Guangcheng Wu¹, Yong Wu¹, Ruihua Zhang¹, Yang Jiao¹, Xingang Zhao¹, Xiao-Yang Chen¹, Huang Wu¹, Charlotte L Stern¹, Yuguo Ma⁴, Yunyan Qiu⁵, Michael R Wasielewski^{1

2

3}, J Fraser Stoddart^{1

6

7

8}

Affiliations

¹ Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
² Center for Molecular Quantum Transduction, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
³ Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208, United States.
⁴ Beijing National Laboratory for Molecular Sciences, Centre for the Soft Matter Science and Engineering, The Key Lab of Polymer Chemistry & Physics of the Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
⁵ Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore.
⁶ Stoddart Institute of Molecular Science, Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
⁷ ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 311215, China.
⁸ School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.

PMID: 37578165
DOI: 10.1021/jacs.3c04340

Abstract

Organic trisradicals featuring threefold symmetry have attracted significant interest because of their unique magnetic properties associated with spin frustration. Herein, we describe the synthesis and characterization of a triangular prism-shaped organic cage for which we have coined the name PrismCage⁶⁺ and its trisradical trication─TR^3(•+). PrismCage⁶⁺ is composed of three 4,4'-bipyridinium dications and two 1,3,5-phenylene units bridged by six methylene groups. In the solid state, PrismCage⁶⁺ adopts a highly twisted conformation with close to C₃ symmetry as a result of encapsulating one PF₆^- anion as a guest. PrismCage⁶⁺ undergoes stepwise reduction to its mono-, di-, and trisradical cations in MeCN on account of strong electronic communication between its 4,4'-bipyridinium units. TR^3(•+), which is obtained by the reduction of PrismCage⁶⁺ employing CoCp₂, adopts a triangular prism-shaped conformation with close to C_2v symmetry in the solid state. Temperature-dependent continuous-wave and nutation-frequency-selective electron paramagnetic resonance spectra of TR^3(•+) in frozen N,N-dimethylformamide indicate its doublet ground state. The doublet-quartet energy gap of TR^3(•+) is estimated to be -0.08 kcal mol^-1, and the critical temperature of spin-state conversion is found to be ca. 50 K, suggesting that it displays pronounced spin frustration at the molecular level. To the best of our knowledge, this example is the first organic radical cage to exhibit spin frustration. The trisradical trication of PrismCage⁶⁺ opens up new possibilities for fundamental investigations and potential applications in the fields of both organic cages and spin chemistry.