Diverse magnetic and electrical properties of molecular solids containing the thiazyl radical BDTA

Abstract We have examined the crystal structures and the electrical and magnetic properties of the molecular compounds of a thiazyl radical, 1,3,2-benzodithiazolyl (abbreviated as BDTA). BDTA was found to be a useful building block for molecular conductors and magnets because it can operate as a counter cation, a donor or a ligand, depending on its charge. (i) A charge-transfer complex, [BDTA][TCNQ], crystallizes into a uniform segregated stacking structure with a short contact between the donor and acceptor columns. In spite of the partial charge transfer between the two components, this complex exhibits semiconductive behaviour, probably due to a large electron correlation on BDTA. (ii) The crystal structure of [BDTA][Ni(mnt)2] (mnt = maleonitriledithiolate) consists of alternating stacking columns of S = 0 [BDTA]+ and S = 1/2 [Ni(mnt)2]−, in which a ferromagnetic coupling operates between the [Ni(mnt)2]− anions through the [BDTA] + cation. (iii) [BDTA]2[Cu(mnt)2] consists of an alternating stack of a head-to-head [BDTA]+ dimer and a planar [Cu(mnt)2]2− dianion. Short intermolecular S⋯S contacts between the stacks give rise to an ideal 1D Heisenberg antiferromagnetic chain of [Cu(mnt)2]2− with a coupling constant of J/kB = 16–17 K. (iv) The crystal structure of [BDTA]2[Co(mnt)2] is similar to that of [BDTA]2[Cu(mnt)2] at 253 K, but this salt undergoes a phase transition at 190 K, below which a partial electron transfer occurs from [Co(mnt)2]2− to one of the [BDTA]+ cations along with formation of a coordination bond. (v) [BDTA][Ni(dmit)2]2 (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) exhibits room-temperature conductivity of 0.1 S cm−1 and semiconductive behaviour over the range 80–200 K, which can be interpreted in terms of multi-conducting bands.