[Fe(sal2-trien)][Ni(dmit)2]: towards switchable spin crossover molecular conductors

Abstract

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...

Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

“…Compounds of type (NR 4 )[M(dmit) 2 ] x (x>1), with nonintegral oxidation state, display interesting electron transport features. Combining SC and electrical conductivity was the aim of Dorbes et al [11] [12]. Analogously, similar properties have been studied on the salts of the [Fe(qsal) 2 ] + and Fe(R-salEen)] + complex cations as well [13][14][15][16][17][18][19].…”

“…The aim of the present work was to complete the first observations of Dorbes et al [11] by investigating in more details the effects of temperature and pressure on the spin state and associated properties of the triclinic [Fe(sal 2 -trien)][Ni(dmit) 2 ] complex, which is one of the rare Fe III complexes displaying thermal spin transition with hysteresis. This first-order transition occurs without a change of the space group of the crystal (P ), creating thus an interesting scope for the comparison of experimental observations, especially pressure effects, with theoretical predictions [26].…”

“…The resultant 1:1 compound is built up of slabs of [Fe(sal 2 -trien)] + cations and layers of [Ni(dmit) 2 ] -anions [11], which alternate along the c-axis and spread out onto the ab plane. In the HS state, the SC sites are constituted of severely distorted octahedral [FeN 4 O 2 ] centres, whereas in the LS state, the coordination octahedron is much more regular (Figure 1).…”

Four new spin-crossover salts of [Fe(3-bpp)2]2+ (3-bpp=2,6-bis[1H-pyrazol-3-yl]pyridine)

“…We report here four new salts of 2 ] 2+ , with cyanometallate, thiocyanometallate or BPh 4 -anions. The cyanometallate and thiocyanometallate salts were prepared with a view to examining their fluorescence.…”

“…Examples include salts of spin-crossover cations with metal/dithiolene anions, that can combine spin-crossover with electrical conductivity [4]; magnetic metal/oxalate framework structures with included spin-crossover cations [5,6]; and nanoporous metal-organic frameworks constructed with spin-crossover centres, whose spin-state behaviour is sensitive to the addition or removal of guest solvent [7,8]. These studies have tended to employ a small selection of spin-crossover cation centres, that are robust in solution and can be crystallised in the presence of potentially coordinating anions.…”