| Abstract
| - Synthesis, crystallography, and magnetic characterization of a stable macrocyclic tetranitroxide1, a calix[4]arene, which is functionalized with four tert-butylnitroxides at the upper rim, is described. Insolution, 1 has a 4-fold symmetric fixed cone conformation on the NMR time scale and small, butnonnegligible, exchange interactions between the radicals (30 K > |J/k| ≫1.8 mK). In the solid state,dimerization of one diagonal pair of nitroxides leads to a pinched cone conformation for 1 with strongintradimer antiferromagnetic coupling with |J/k| = 200−300 K (singlet−triplet energy gap, ΔEST ≈ 1 kcal/mol).
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