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. 2026 Jan 26;16(7):5707-5715.
doi: 10.1039/d5ra07308a.

Reverse micelle synthesis and downsizing effects in iron(iii) spin crossover materials

Sharon E Lazaro  1 , Phimphaka Harding  2 , Upsorn Boonyang  3 , Shane G Telfer  4 , Wasinee Phonsri  5 , Keith S Murray  5 , David J Harding  2
Affiliations

Reverse micelle synthesis and downsizing effects in iron(iii) spin crossover materials

Sharon E Lazaro et al. RSC Adv. .

Abstract

We report the reverse micelle synthesis, structural characterisation and magnetic properties of iron(iii) spin crossover (SCO) nanomaterials based on [Fe(qsal)2]NO3, [Fe(qsal-I)2]OTf and [Fe(qsal-I)2]NTf2 using sodium dioctylsulfosuccinate (NaAOT) and hexane. The synthesis and characterization of a new complex, [Fe(qsal)2]NO3·EtOH is also reported. Systematic variation of micellar conditions including surfactant content in the polar and organic phases, reaction time, and solvent choice enabled the controlled formation of parallelogram, plate-like and rod-like shapes for [Fe(qsal)2]NO3, [Fe(qsal-I)2]OTf and [Fe(qsal-I)2]NTf2, respectively, as confirmed by FESEM. Magnetic studies reveal abrupt spin crossover with a narrower hysteresis width compared to the bulk materials. Nanomaterials of [Fe(qsal-I)2]OTf exhibit a 4 K hysteresis (T 1/2↑ = 231 K and T 1/2↓ = 227 K) while those of [Fe(qsal-I)2]NTf2 display a 27 K hysteresis (T 1/2↑ = 275 K and T 1/2↓ = 248 K) comparable to the bulk. The results demonstrate that reverse micelle methods can reliably produce iron(iii) SCO nanomaterials, advancing their potential for integration into functional devices.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. (a) View of the asymmetric unit of 1 at 293 K and (b) π–π stacking between the aromatic moieties and C–H⋯O interactions between the NO3− anion and the [Fe(qsal)2]+ units.
Fig. 2
Fig. 2. Visual representation of the reverse micelle synthesis of the [Fe(qsal)2]NO3 nanoparticles.
Fig. 3
Fig. 3. FESEM images of [Fe(qsal)2]NO3 materials synthesized using (a) H2O (b) EtOH and (c) MeOH as the solvent for the Fe3+ precursor. The Hqsal ligand and iron(iii) micellar concentrations were fixed at 2.0 g of NaAOT.
Fig. 4
Fig. 4. FESEM images and DLS size distribution graphs of [Fe(qsal)2]NO3 materials synthesized using (a) 0.5 g (b) 1.0 g (c) 2.0 g and (d) 4.0 g of NaAOT in MeCN for the ligand micelle solution. The iron(iii) micellar concentration is fixed at 2.0 g of NaAOT.
Fig. 5
Fig. 5. FESEM images and DLS size distribution graphs of [Fe(qsal)2]NO3 materials synthesized using (a) 0.5 g (b) 1.0 g (c) 2.0 g and (d) 4.0 g of NaAOT in water for the iron(iii) micelle solution. The ligand micellar concentration is fixed at 2.0 g of NaAOT.
Fig. 6
Fig. 6. FESEM images and DLS size distribution graph for (a) 3 and (b) 4 using a concentration of 2 g of NaAOT in both the ligand and iron(iii) micellar phases.
Fig. 7
Fig. 7. χ M T versus T plot of the bulk and nanomaterials of [Fe(qsal-I)]OTf.
Fig. 8
Fig. 8. χ M T versus T plots of the bulk and nanomaterials of 4.
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