Magnetic Coupling and Anisotropy in a Series of Mixed Chain Charge‐Transfer Salts [M(Cp*)2][M′(tds)2] (M = Fe, Mn, Cr; M′ = Ni, Pt)

Abstract

AbstractThe preparation of new charge‐transfer (CT) salts based on the decamethylmetallocenium donors (D), [M(Cp*)2] (M = Mn, Cr), and on the bis[bis(trifluoromethyl)ethylene diselenolato]metalate(III) acceptors (A), [M′(tds)2] (M = Ni, Pt), yielded four new members of the family of CT salts [M(Cp*)2][M′(tds)2] {M/M′ = Fe/Ni (1), Fe/Pt (2), Mn/Ni (3), Mn/Pt (4), Cr/Ni (5), Cr/Pt (6)}. Their crystal structures consist of anarrangement of parallel mixed chains, DADADA, with short D–A contacts and large interchain separations. The CT salts 1–5 are isostructural and 6 shows minor differences in the interchain arrangements. The analysis of the intermolecular contacts, in the framework of the McConnell I model, provides a fair interpretation of the magnetic coupling. The behavior of these salts is dominated by the ferromagnetic (FM) D–A intrachain interactions. Coexisting weaker antiferromagnetic (AF) interchain couplings induce AF transitions in 2, 3, 4, and 6, with TN = 3.3, 2.1, 5.8, and 5.2 K, respectively. The intrachain coupling and the TN values of the CT salts based on the [M(Cp*)2] (M = Fe, Mn) donors (1, 2, 3, and 4) were found to be in good agreement with those predicted by the mean field model. Compounds 5 and 6 exhibit weaker intrachain coupling and lower critical temperatures than those predicted by that model, which is attributed to weaker D–A interactions. The study of the low temperature behavior of the salts 3, 4, and 6 allowed the disclosure of the effect of the magnetic anisotropy of the donors. The CT salts based on highly anisotropic donors, such as 3 and 4, show metamagnetic (MM) behavior, with phase diagrams that include a paramagnetic (PM) and an AF phase, as previously observed for 2. In the phase diagram of 6, where the [Cr(Cp*)2] donor does not show magnetic anisotropy, a spin‐flop (SF) phase is present in addition to the PM and AF phases. This is the first time an SF phase was observed in [M(Cp*)2]‐based CT salts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)