Metamagnetism in linear chain electron-transfer salts based on decamethylferrocenium and metal–bis(dichalcogenate) acceptors

The crystal structure of the electron-transfer (ET) salts [Fe(Cp*)2][M(tds)2], with M=Ni (1) and Pt (2), consists of an array of parallel alternating donors, [Fe(Cp*)2]radical dot+, and acceptors, [M(tds)2]radical dot−, ⋯DADADA⋯, stacks. For T>20 K, the magnetic susceptibility follows a Curie–Weiss behavior, with θ values of 8.9 and 9.3 K for 1 and 2, respectively. A metamagnetic behavior was observed in 2, with TN=3.3 K and HC=3.95 kG at 1.7 K, resulting from a high magnetic anisotropy. A systematic study of the intra and interchain magnetic interactions was performed on 1, 2 and other ET salts based on decamethylferrocenium and on metal–bis(dichalcogenate) acceptors, with a similar crystal structure. The observed magnetic behavior of these compounds is consistent with the presence of strong ferromagnetic intrachain DA interactions and weaker antiferromagnetic interchain interactions, predicted by the McConnell I model. A variety of interionic interchain contacts were found in these ET salts (AA, DD and DA) and these contacts were observed to give rise to antiferromagnetic interchain coupling. Although it was only observed in the case of 2 and [Fe(Cp*)2][Ni(edt)2], metamagnetism is expected to occur at lower temperatures in the other ET salts due to weaker intra and interchain coupling.