S = 1 Tetraazacyclophane Diradical Dication with Robust Stability: A Case of Low-Temperature One-Dimensional Antiferromagnetic Chain

摘要

One-dimensional (1D) spin-1 (S = 1) chain of organic radicals with low local magnetic anisotropy may provide a better understanding of the low-dimensional magnetism. We report solid-state studies, including single crystal X-ray crystallography, of air-stable tetraazacyclophane diradical dication salt 1 ~(2·2+)·2[Al(OC(CF_(3))_(2)CH_(3))_(4)]~(−) with a triplet ground state (ΔE _(ST) ≈ 0.5 kcal mol~(–1)). The magnetic behavior for 1 ~(2·2+) at low temperature is best modeled by 1D spin S = 1 Heisenberg chain with intrachain antiferromagnetic coupling of J ′/k = −5.4 K, which is associated with the interaryl C···C contacts, including π–π interactions. Zero-field splitting value, |D /hc | ≈ 5.6 × 10~(–3) cm~(–1), for 1 ~(2·2+) is rather small; thus, the 1D chains are characterized by the high degree of isotropicity |D /2J ′| ≈ 7.5 × 10~(–4). The diradical dication salt possesses extraordinary stability with onset of decomposition at temperature of about 180 °C (∼450 K), based on thermogravimetric analysis and EPR spectroscopy.