Solvent modified spin crossover in an iron(iii) complex: phase changes and an exceptionally wide hysteresis

Abstract

The impact of solvent on spin crossover is explored with T 1/2 varying by 200 K and hysteresis up to 80 K.

Unusual Magneto‐Structural Features of the Halo‐Substituted Materials [FeIII(5‐X‐salMeen)2]Y: a Cooperative [HS‐HS]↔[HS‐LS] Spin Transition

“…The room temperature values of χ M T for 1 – 4 , which occur in the range 4.06–4.28 cm 3 K mol −1 , are consistent with the spin‐only value for HS iron(III) (χ M T ≈4.38 cm 3 K mol −1 ). They also concur with literature values in the range 3.80–4.50 cm 3 K mol −1 for closely related ferric spin‐crossover materials; although some of these reported values are somewhat low . The spin conversion in 1 – 4 , evidenced by the decrease in the values of χ M T with temperature, culminates in a plateau with a width of 115 K (140‐25 K) for 2 – 4 and 85 K (110‐25 K) for 1 .…”

“…It was not until very recently that the literature witnessed two other salEen‐based examples of SCO materials exhibiting an abrupt spin transition with hysteresis, namely [Fe III (4‐OMe‐ salEen) 2 ]NO 3 and [Fe III (5‐Br‐salEen) 2 ]ClO 4 . Indeed, in general, there is a paucity of iron(III) spin‐crossover complexes that display the much sought‐after unique spin‐transition features such as abrupt and hysteretic, symmetry‐breaking, stepwise and wide [HS‐LS] plateau, and structural phase transition, attributable to cooperativity amongst the paramagnetic centres in the crystal lattice through noncovalent intermolecular forces. Within the [Fe III (R 1 ,R 2 ‐salRen) 2 ] + system, observation of cooperative spin crossover is even rarer.…”

“…Modulation of spin‐crossover properties in iron(III)‐salicylaldimine systems by introducing halogen substituents into the para position of the phenolate moiety has been demonstrated spectacularly by the complexes [Fe(qsal‐5‐X) 2 ]Y (qsal=quinolylsalicylaldiminate; X=halogen; Y= counter anion) . Within the family [Fe III (R 1 ,R 2 ‐salRen) 2 ]Y, only three crystallographically characterized 5‐halo‐substituted members are known, namely [Fe III (5‐Br‐salEen) 2 ]Cl ⋅ 0.5 H 2 O, [Fe III (5‐Br‐ salEen) 2 ]ClO 4 and [Fe III (5‐I‐salEen) 2 ]ClO 4 .…”

Elucidating the Structural Chemistry of a Hysteretic Iron(II) Spin‐Crossover Compound From its Copper(II) and Zinc(II) Congeners

“…Most such applications require compounds exhibiting abrupt thermal SCO with significant thermal hysteresis, which are bistable at temperatures inside the hysteresis loop . While examples with hysteresis widths of up to 140 K are known, SCO materials showing hysteresis wider than 40 K are still unusual . As a result, most SCO application studies are carried out with just two types of coordination polymer materials, with suitably hysteretic SCO that also spans room temperature …”

A New Family of Heterometallic LnIII[12-MCFeIIIN(shi)-4] Complexes: Syntheses, Structures and Magnetic Properties

“…Nevertheless, few MCs consisting of Fe-Ln ions have been found, except that several homometallic [9- [24,[32][33][34]. Due to the high magnetic anisotropy and large spin-orbital coupling of Ln III ions, as well as high-spin Fe III with S = 5/2 spin state presenting Spin Crossover (SCO) [35][36][37][38], it is meaningful to explore macrocyclic polynuclear complexes with Fe-Ln MCs structures and magnetic properties.…”