Crystallography and magnetism of 3-(N-tert-butyl-N-aminoxyl)benzoic acid

3-(N-tert-Butyl-N-aminoxyl)benzoic acid is a stable red solid that crystallizes to form chains of nitroxide to aryl CH contacts, with the pairs of such antiparallet chains joined by complementary carboxylic acid two-point hydrogen bonds. Although it strongly adsorbs to silica gel, it does not show solution phase ESR evidence of discrete triplet state radical pairing. Solid-state magnetic susceptibility studies show antiferromagnetic downturn at lower temperatures, with a change in slope at about 10 K in Curie-Weiss plots. The results suggest either a phase change at low temperatures, or the presence of multiple competing exchange interactions. (c) 2005 Elsevier Ltd. All rights reserved.