An organic radical solid solution with strong ferromagnetic exchange

A solid-solution crystallization of two organic radicals to give strong 1D chain ferromagnetic (FM) exchange, controlled by hydrogen-bonding assembly of the radicals was analyzed. The hydrogen-bonded chains in the benzimidazole group assembled nitronylnitroxide radical groups in BImNN into T-stacks that favor FM exchange by a through-space spin polarization (SP) model. Favorable contacts occurred when spin orbitals of opposite spin density overlap, leading in the case of BImNN to (FM) exchange. Magnetic measurements supported the SP model, showing 1D Heisenberg chain FM exchange in BImNN. X-ray diffraction analysis of several single crystals of the mixture confirmed that the fluorinated and nonfluorinated radicals intimately co-mingle. The contacts should induce FM exchange along the whole chain of T-stacks, based on qualitative spin orbital overlap. Results show that structural changes to BImNN can give significant changes in solid-state crystal packing and magnetic-exchange behavior.