AbstractThree 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 Mössbauer 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)