Radicals organized by disk shaped aromatics – polymorphism and co-crystals that tune inter-electron exchange

Abstract

Polymorphism's effect on intermolecular packing is a critical consideration for organic magnetic materials. Magnetostructural studies of pyrene-1-yl (Pyr) bearing nitronylnitroxide (NN) and iminoylnitroxide (IN) radicals found that PyrNN gives two allotropes: one has spin-paired dyads with ΔE = J/k ≈–178 K, and one is half spin-paired with ΔE = J/k ≈ −102 K, and half paramagnetic. PyrIN also gives two allotropes, one an anti conformation that is spin paired with ΔE = J/k = −410 K, and one a paramagnetic system having a syn conformation. PyrNN co-crystallizes with C₆F₆ in 2 : 1 ratio with a methyl to nitroxide contact network exhibiting low dimensional 1-D or 2-D antiferromagnetic exchange.