High-Spin Polyarylmethyl Polyradical:  Fragment of a Macrocyclic 2-Strand Based upon Calix[4]arene Rings

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.