Vapochromic effect in switchable molecular-based spin crossover compounds

Abstract

We present here for the first time an exhaustive compilation of all systems in which the interaction between the coordination compounds and the vapour analytes leads to a colour change due to a spin transition in the metal centre at room temperature.

The effect of inert dopant ions on spin-crossover materials is not simply controlled by chemical pressure

“…[10][11][12] That switching functionality is being exploited in molecular electronics 8,13 and nanoscience, 5,14,15 while SCO materials are being investigated for solid state refrigeration, [16][17][18][19] mechanical actuation, 7,[20][21][22] thermochromic printing 23,24 and other macroscopic applications. 6,[25][26][27][28] Spin-transitions are also useful probes of crystal lattice dynamics, which allow the nucleation, growth and decay of new phases to be observed in real time. 29,30 Most of these applications require materials undergoing first order spin-transitions, which arise from an interplay between the individual switching centres and the surrounding lattice.…”

“…10–12 That switching functionality is being exploited in molecular electronics 8,13 and nanoscience, 5,14,15 while SCO materials are being investigated for solid state refrigeration, 16–19 mechanical actuation, 7,20–22 thermochromic printing 23,24 and other macroscopic applications. 6,25–28 Spin-transitions are also useful probes of crystal lattice dynamics, which allow the nucleation, growth and decay of new phases to be observed in real time. 29,30…”

Iron(II) Complexes of 2,6-Di[4-(ethylcarboxy)pyrazol-1-yl]pyridine with Reversible Guest-Modulated Spin-Crossover Behavior

“…Many examples of guest-sensitive SCO compounds have been reported in polymeric porous coordination polymers or metal–organic frameworks (MOFs), as they contain extended networks of chemical bonds and pores that prevent the network from collapsing after removal of the guest molecules and provide a pathway for the loss and uptake of the solvent molecules . However, in the last few years several molecular-based SCO compounds have been reported to undergo absorption, desorption, or substitution of solvent molecules coupled to a change of their spin state, which can be accompanied by single-crystal to single-crystal (SCSC) transformations. − …”

From a mononuclear FeIIL2 complex to a spin crossover FeII4L6 cage by symmetric ligand architecture modification: insights into the ammonia gas sensing mechanism

“…20 Good candidates for alleviating these defects are Fe II coordination complexes whose spin transition (highspin (HS) 2 low-spin (LS)) is triggered by the presence of the target analyte, while the transition process may be accompanied by a colour change. 21,22 Also, some Fe II -based compounds grown in aqueous solutions or mixed with water can somewhat mitigate or eliminate the effect of humidity on sensing performances. Meanwhile, Fe II coordination complexes possess the intrinsic nature of being a chemosensor in that the metal ions are highly sensitive to slight changes in the surrounding coordination environments driven by guest intercalation or delamination.…”