Spin Frustration in the Triradical Trianion of a Naphthalenediimide Molecular Triangle

Crystalline supramolecular frameworks consisting of charged molecules, held together by hydrogen bonds and Coulomb interactions, have attracted great interest because of their unusual structural, chemical, electronic, and magnetic properties. Herein, we report the preparation, structure, and magnetic properties of the triradical trianion of a shape-persistent chiral equilateral molecular triangle having three naphthalene-1,4:5,8-bis(dicarboximide)s ((+)-NDI-Δ^3(-•)). Single-crystal X-ray diffraction of its tris(cobaltocenium) salt ([(+)-NDI-Δ^3(-•)(CoCp₂⁺)₃]) reveals accessible one-dimensional tubular cavities, and variable-temperature electron paramagnetic resonance spectroscopy shows that a dilute solution of [(+)-NDI-Δ^3(-•)(CoCp₂⁺)₃] in an organic glass has a spin-frustrated doublet ground state and a thermally accessible quartet state. Furthermore, SQUID magnetometry from 5 to 300 K of solid [(+)-NDI-Δ^3(-•)(CoCp₂⁺)₃] shows ferromagnetic ordering with a Curie temperature T_C = 20 K. The successful preparation of hybrid ionic materials comprising macrocyclic triradical trianions with spin-frustrated ground states and accessible 1D pores offers routes to new organic spintronic materials.