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

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.