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RESEARCH PRODUCT

Towards Molecular Conductors with a Spin‐Crossover Phenomenon:Crystal Structures, Magnetic Properties and Mössbauer Spectra of[Fe(salten)Mepepy][M(dmit) 2 ] Complexes

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Three new iron(III) compounds of formula [Fe(salten)Mepepy][M(dmit)2]·CH3CN (M = Ni, Pd, Pt; H2salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate); Mepepy = 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl) ethane; dmit2– = 1,3-dithiole-2-thione-4,5-dithiolato) have been synthesised and the crystal structure of each compound has been solved at different temperatures. The structures consist of alternating layers of [M(dmit)2]– units and [Fe(salten)Mepepy] cations. In the Ni compound photo-isomerisation of the Mepepy ligand can be observed in dichloromethane solution. The temperature dependence of the magnetic susceptibility of the compounds reveals a gradual S = 5/2 blabla S = 1/2 spin crossover of the FeIII ions. This phenomenon is confirmed by Mossbauer spectroscopy for the Ni compound, which also reveals a magnetic component at 4.5 K with a hyperfine magnetic field, Hi, of 442(3) Oe. Theoretical analysis of the thermal variation of the high-spin proportion allows us to calculate the thermodynamical parameters of the spin-crossover behaviour in this compound: energy-gap (Δ) = 1536 cm–1, entropy change (ΔS) = 33 J K–1 mol–1 and a cooperative interaction, J, of 0 cm–1 (non-cooperative spin crossover). The fractional oxidation state complex [Fe(salten)Mepepy][Ni(dmit)2]3 has been obtained after electrooxidation of [Fe(salten)Mepepy][Ni(dmit)2] in acetonitrile. It exhibits a gradual spin conversion coupled with antiferromagnetic interactions. Its room temperature electrical conductivity is 0.1 S cm–1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)