Crystallography and Magnetism of Two 1-(4-Nitroxylphenyl)pyrroles

Stable radicals 1-(4-(N-tert-butyl-N-aminoxyl)phenyl)pyrrole (BNPP) and 1-(4-(N-[para-methoxyphenyl]-N-aminoxyl)phenyl)pyrrole (MNPP) were synthesized and characterized by crystallography and magnetism.
BNPP crystals exhibit 1-D chains of intermolecular nitroxide NO to nitroxide CH3 contacts, but
polycrystalline magnetic susceptibility measurements show quite small antiferromagnetic (AFM) exchange
interactions. MNPP shows stronger AFM exchange interactions that appear to be associated with a 2-D
planar mesh of crystallographic nitroxide to nitroxide (N)O···N(O) contacts of 4.0−4.2 Å. The AFM
behavior of MNPP can be fitted to a 2-D square planar Heisenberg antiferromagnetic exchange model
with J/k = (−)0.78 ± 0.04 K and mean field constant θ = (−)0.77 ± 0.12 K.