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

Abstract

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 α-nitronyl nitroxide) cationic radical have been studied. Both crystals contain one-dimensional p-EPYNN chains with alternate head-to-tail orientation. In this chain a ferromagnetic 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(dmit)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 is 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(dmit)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 electron in [Au(dmit)2]-, the presence of the unpaired electron in the frontier orbital of [Ni(dmit)2]- plays an important role in the formation of an antiferromagnetic molecular spin ladder.