Annelated triple-calix[4]arene-based tetradecaether 1- (OMe) 14 is synthesized. Its three isomers, 1X- (OMe) 14 , 1Y-(OMe) 14 , 1Z-(OMe) 14 , are isolated and characterized. The corresponding triarylmethyl carbopolyanion is prepared and oxidized to polyradical 1. SQUID magnetometry for 1 in THF-d 8/2-MeTHF gives S = 6.2, below the theoretical value of 7 expected for strong ferromagnetic coupling between 14 “unpaired” electrons. Chemical quenching studies suggest that approximately one deuterium from the deuterated solvent is incorporated in 1, thus accounting in part for S < 7. Study of the temperature dependence of magnetization indicates that ferromagnetic coupling between “unpaired” electrons is not very strong in 1; i.e., the thermal population of low-spin excited states is detected in the cryogenic temperature range. Upon exposure of 1 in THF-d 8/2-MeTHF to ambient temperature for 30 min, a narrow distribution of spin systems with an “average” S = 2.5 is obtained; upon a longer exposure time of 24 h, an “average” S = 1 is produced.

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Synthesis, crystallography, and magnetic characterization of a stable macrocyclic tetranitroxide 1, a calix[4]arene, which is functionalized with four tert-butylnitroxides at the upper rim, is described. In solution, 1 has a 4-fold symmetric fixed cone conformation on the NMR time scale and small, but nonnegligible, 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 strong intradimer antiferromagnetic coupling with /J/k/ = 200-300 K (singlet-triplet energy gap, DeltaE(ST) approximately 1 kcal/mol).