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)

The preparation of new charge-transfer (CT) salts based on the decamethylmetallocenium donors (D), [M(CP*)(2)] (M = Mn, Cr), and on the bis [bis(trifluromethyl) 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 an arrangement 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 T-N = 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 iriodel. 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 meta-magnetic (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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).