Solvent Effects on the Structural and Magnetic Properties of Fe^III Spin-Crossover Complexes

Abstract

Molecular devices based on spin-crossover (SCO) compounds are important targets for molecular electronics. In this study, six air-stable FeIII complexes have been prepared: [Fe­(naphBzen)2]Cl (1), [Fe­(naphBzen)2]­Cl·0.5hexane (1·0.5hexane); [Fe­(naphBzen)2]­Cl·2CHCl3·1.15hexane (1·2CHCl3·1.15hexane), [Fe­(naphBzen)2]Br (2), [Fe­(naphBzen)2]­Br·0.5hexane (2·0.5hexane), and [Fe­(naphBzen)2]­Br·2CHCl3 (2·2CHCl3). The hexane solvates are isostructural, crystallizing in the tetragonal space group I41/a. Weak van der Waals interactions between the cations result in the Fe1 and Fe2 centers packing into chiral chains and exhibiting two-step SCO. In contrast, the nonisostructural CHCl3 solvates have a single Fe center and crystallize in the triclinic space group P1̅ and are LS up to 350 K. The solvent-free systems are also not isostructural with [Fe­(naphBzen)2]­Cl, crystallizing in the triclinic space group P1̅, while [Fe­(naphBzen)2]Br undergoes a phase transition from tetragonal P43 to P43212 upon heating from 150 to 280 K. In both cases the compounds are trapped in the LS state. Magnetic data reveals that SCO occurs only in the hexane solvates, indicating that even very weak interactions can be critical in observing spin-crossover behavior.

Push and Pull Effect of Methoxy and Nitro Groups Modifies the Spin-State Switching Temperature in Fe(III) Complexes

“…These data are in good agreement with the values of Δ H and Δ S reported in the literature. , The T 1/2 values for 1 , 2 and 3 , are 241, 277, and 318 K, respectively, indicating that the transition temperature increases as we go from 1 to 3 . The linear trend of the susceptibility plot is comparable to liquid state magnetic data of other similar complexes. ,, …”

“…The linear trend of the susceptibility plot is comparable to liquid state magnetic data of other similar complexes. 18 , 20 , 29 …”

“…The linear trend of the susceptibility plot is comparable to liquid state magnetic data of other similar complexes. 18,20,29 EPR Measurements. For a low-spin Fe(III) complex, there is only one unpaired electron (S = 1/2); thus, the compound should exhibit only one signal.…”

Effect of Methoxy Ligand-Substituent and NCE Coligands in Tuning T1/2 of Coordinatively Elastic Fe(II) Spin Crossover Complexes

“…On the other hand, understanding around the predictability or control over the spin states is still a great challenge. In terms of studies in solution, promising results emerge from the recent literature where excellent linear correlations are obtained between switching temperatures of the complexes with various parameters including Hammett constant, alkyl chain length, 15 N chemical shifts, polarity index of the solvents, and redox potentials. − However, the hurdle in predictable tuning in the solid state is that, as we know from our earlier work and from the literature, the SCO phenomenon is highly sensitive to the lattice solvent, the counterion, the π–π stacking, and the effects of crystal packing, which can either lock the metal ion in one spin state, or at least the spin transition in crystalline systems is highly dependent on these factors. , So achieving predictable tuning in the solid state even within a family of compounds is a great challenge. One way of tuning the spin switching temperatures ( T 1/2 ) in metal complexes is through the design of the ligands.…”

High-Temperature Spin Crossover in FeIII N4O2 Complexes Incorporating an [R-sal2323] Backbone

“…The literature in SCO is dominated by Fe II compounds, which is due in part to its easily distinguished spin states, ,, although Fe III also has been well-studied. ,,, Recent studies have highlighted magnetostructural dependence arising from the delicate interplay of substituent, anion and solvent selection on the exhibition and behavior of SCO in Fe III mononuclear complexes. − Practically, Fe III is a good candidate for use in devices, because it is not susceptible to oxidation, and its 3d 5 electron configuration gives rise to a strong magnetic signal in the HS state ( S = 5/2), with a comparatively weak signal in LS ( S = 1/2) . Coordination spheres that have been shown to favor SCO in Fe III compounds include N 2 O 2 S 2 , N 3 O 2 S, N 5 O , and N 6 , although the most commonly reported example is N 4 O 2 . ,, One ligand archetype which affords this coordination environment is the H 2 Salen family, which has been shown to enable SCO in Fe III and other metals. ,− Studies have investigated the effect of the tetraamine backbone length on the spin state. , Common variations of the tetraamine backbone include the following: sal 2 222, sal 2 232, and sal 2 323 (Figure ).…”