Synthesis, Structure and Physical Properties of the First One-Dimensional Phenalenyl-Based Neutral Radical Molecular Conductor

We report the preparation, crystallization, and solid-state characterization of a benzyl-substituted
spirobiphenalenyl radical. The crystal structure shows that the radical is monomeric in the solid state, with
the molecules packed in an unusual one-dimensional (1-D) fashion that we refer to as a π-step stack. This
particular mode of 1-D stacking is forced on the lattice arrangement by the presence of the orthogonal
phenalenyl units that were specifically incorporated to prevent the crystallization of low-dimensional
structures. The structure shows that this strategy is effective, and neighboring molecules in the stack can
only interact via the overlap of one pair of active (spin-bearing) carbon atoms per phenalenyl unit, leading
to the π-step structure in which the remaining four active carbon atoms per phenalenyl unit do not interact
with nearest neighbor molecules. The magnetic susceptibility data in the temperature range 4−360 K may
be fit to an antiferromagnetic Heisenberg S = 1/2 linear chain model with intrachain spin coupling J =
−52.3 cm-1. Despite the uniform stacking, the material has a room temperature conductivity of 1.4 × 10-3
S/cm and is best described as a Mott insulator.