Novel magnetic properties of heterocyclic thiazyl radicals

We studied the magnetic properties of a heterocyclic thiazyl radical, TTTA (1,3,5-trithia-2,4,6-triazapentalenyl). The temperature dependence of the p aramagnetic susceptibility of TTTA indicates a first-order phase transition between a paramagnetic high-temperature (HT) phase and a diamagnetic low-t emperature (LT) phase with a surprisingly large hysteresis loop: T-cl = 230 K and T-cl = 305 K. The room temperature (290 K) is within this loop, so t hat TTTA is bistable at this temperature. The X-ray crystal analyses reveal that the HT phase consists of a regular stacking chain of TTTA in contrast a strong dimerization in the LT phase. We also describe the crystal struct ure and the magnetic properties of the 1:1 complex of TTTA and Cu(hfac)(2) (bis(hexafluoroacetylacetonato)copper(II)) The structure consists of a 1D a lternating chain of the components, in which TTTA acts as a bidentate ligan d bridging the Cu(II) ions. The magnetic measurements reveal a ferromagneti c property. (C) 2001 Elsevier Science Ltd. All rights reserved.