A cooperative spin transition behaviour with a wide hysteresis loop (30 K) around 240 K has been observed, for the first time, in a salt based on the redox active [Ni(dmit) 2 ] 2 , anion and the [Fe(sal 2 -trien)] + spin crossover cation.Supramolecular synthesis of multicomponent materials from spontaneous assembly of molecules into stable and noncovalently joined aggregates is one of the most useful approaches to obtain new functional molecular materials. 1 In this context, spin crossover (SC) building blocks are particularly suitable and represent one of the best examples of molecular bistability. They may be switched between the low-spin (LS) and high-spin (HS) states leading to distinctive changes in magnetism, colour and structure, which may be induced by variation of temperature and/or pressure and by light irradiation. 2 Strong signal generation and hysteresis is observed in some cases when the molecular structural changes associated to SC are cooperatively transmitted in the lattice. 3 Electrical conductivity is a fundamental property of matter currently investigated in the realm of the molecular science. 4 For instance, electronic conduction derived from dithiolene complexbased compounds has received much attention. 5 In particular, compounds of the type (NR 4 ) x [M(dmit) 2 ] (0 , x , 1) with nonintegral oxidation state based on 2-thioxo-1,3-dithiole-4,5-dithiolato (dmit) (NR 4 + 5 tetraalkylammonium cation, M 5 Ni, Pd, Pt) present interesting electric properties. Considering the anionic character of the [Ni(dmit) 2 ] n2 species (Scheme 1, left) and its redox lability as well as the cationic nature and redox stability of most iron(III) SC complexes such as [Fe(sal 2 -trien)] + (Scheme 1, right), 6 we have decided to combine them as building blocks to investigate the possible synergy properties stemming from the coexistence of SC and electronic conduction in the same lattice. 7 As a first step, here we report the synthesis{ and characterisation of the system [Fe(sal 2 -trien)][Ni(dmit) 2 ] (1), which represents the first [Ni(dmit) 2 ] based SC compound.The structure of 1 has been investigated at 295 and 180 K for the HS and LS states, respectively. § Compound 1 is made up of slabs of [Fe(sal 2 -trien)] + cations and layers of [Ni(dmit) 2 ] 2 anions, which alternate along the c-axis and spread out onto the ab plane (Fig. 1). In the HS state, the SC sites are constituted of severely distorted octahedral [FeN 4 O 2 ] centres (Fig. 2, left). The average Fe-N and Fe-O bond distances are 2.155(3) and 1.909(2) s, respectively.The three diagonals of the octahedron, defined by the bonds N(amine)-Fe-O(phenoxo), {N(amine) 5 N2, N3} differ strongly from 180u (155.7(1)-159.0(1)u) while the remaining, defined by N(imine)-Fe-N(imine), is 178.3(1)u {N(imine) 5 N1, N4}. Consequently, the average trigonal distortion W 5 60u 2 H (H is the angle formed by two opposite faces of the octahedron) is 10.9u. These structural features are similar to those already reported for different salts and solvates of the same cationic com...

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Three new compounds based on the cationic complex [Fe(III)(3-R-salEen)(2)]+ (salEen stands for N-(2-ethylamino)ethyl)-salicylaldimine, R = H, CH(3)O) with the electroactive Ni(dmit)(2) species as a counterion (dmit stands for 1,3-dithia-2-thione-4,5-dithiolato) have been synthesized and structurally and magnetically characterized. Compound 1 ([Ni(dmit)(2)][Fe(3-OMe-salEen)(2)]. CH(3)OH) shows an apparent hysteresis loop, due to an irreversible desolvatation process. Compound 2 ([Ni(dmit)(2)](NO(3))[Fe(salEen)(2)](2)) exhibits a gradual and incomplete spin transition. Compound 3 ([Ni(dmit)(2)](5)[Fe(salEen)(2)](2), 6CH(3)CN) is a fractional oxidation state complex, which behaves like a semiconductor and exhibits a gradual but complete spin transition between 300 and 4 K.