Metallocenium Salts of Nickel Bis(α‐thiophenedithiolate) [M(Cp*)2][Ni(α‐tpdt)2] (M = Fe, Mn, Cr) – Metamagnetism and Magnetic Frustration

Abstract

AbstractThe family of charge‐transfer (CT) salts [M(Cp*)2][Ni(α‐tpdt)2] [α‐tpdt = 2,3‐thiophenedithiolate; M = Fe (1), Mn (2), Cr (3)] were prepared. The crystal structure of 3 is similar to that previously reported for 1 and is composed of alternatinglayers each consisting of parallel mixed donor–acceptorD+A–D+A–D+A– chains, and the chains in adjacent layers are perpendicular. A similar crystal structure is expected to occur in 2. The McConnell I model was used to analyze the intermolecular magnetic coupling in this family of compounds. The predicted ferromagnetic (FM) intrachain coupling and the antiferromagnetic (AFM) coupling in the interchain coupling (both intra and interlayer) are in good agreement with the experimental results. The magnetic behavior of these compounds is dominated by FM interactions, which are ascribed to the intrachain FM DA interactions. The low‐temperature magnetic behavior of the new CT salts contrasts that previously reported for metamagnetic compound 1. Whereas CT salt 3 remains paramagnetic down to 1.6 K, 2 shows magnetic behavior that is typical of a frustrated magnet and has a blocking temperature of ca. 4 K. For this compound, the magnetic frustration results from a degenerate ground state in the interlayer spin arrangements. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)