M(dmit)(2) salts with nitronyl nitroxide radical cations (M = Ni and Au, dmit=1,3-dithiol-2-thione-4,5-dithiolate). Nonmagnetic single-chain formation vs antiferromagnetic spin-ladder-chain formation of M(dmit)(2)

The crystal and magnetic structures of the 1:1 salts of [M(dmit)(2)](-) (M = Ni and Au) with the p-EPYNN (p-N-ethylpyridinium cr-nitronyl nitroxide) c ationic radical have been studied. Both crystals contain one-dimensional p- EPYNN chains with alternate head-to-tail orientation. In this chain a ferro magnetic interaction has been found to operate in common. Similarly, there is a common feature in the arrangement of M(dmit)(2); in both crystals M(dm it)(2) forms a one-dimensional chain through intermolecular S...S contacts between the outer rings of the ligand. However, a marked difference exists in the arrangement of these chains. The one-dimensional Au(dmit)(2) chain i s sandwiched between the p-EPYNN chains, resulting in isolation of each one -dimensional Au(dmit)(2) chain. On the other hand, every two chains of Ni(d mit)(2) are sandwiched between the p-EPYNN chains, resulting in the Ni(dmit )(2) ladder-chain formation. In contrast to the absence of the unpaired ele ctron in [Au(dmit)(2)](-), the presence of the unpaired electron in the fro ntier orbital of [Ni(dmit)(2)](-) plays an important role in the formation of an antiferromagnetic molecular spin ladder.