Solvent Dependent Spin‐Crossover and Photomagnetic Properties in an Imidazolylimine Fe^II Complex

Abstract

The synthesis and physico‐chemical characterization of an FeII complex [Fe(L1)3](ClO4)2⋅CH3CN⋅0.5H2O, 1, incorporating a bidentate imidazolylimine‐based ligand are reported. Complex 1 crystallises as the mer‐isomer and the crystal lattice is replete with hydrogen bonding interactions between ClO4− anions, solvent molecules and imidazole N‐H groups. Variable‐temperature structural, magnetic, photomagnetic and optical reflectivity techniques have been deployed to fully characterise the spin‐crossover (SCO) behaviour in 1 along with its desolvated phase, 1⋅desolv. Variable‐temperature (1.8–300 K) magnetic‐susceptibility measurements reveal a broad two‐step full SCO for 1 (T1/2=158 and 184 K) and photomagnetic experiments at 10 K under white‐light irradiation revealed complete photo‐induced SCO. 1⋅desolv displays considerably different magnetic behaviour with sharp single‐step SCO accompanied by a thermal hysteresis (T1/2↑=105 K, T1/2↓=95 K) in addition to full photo‐induced SCO at lower temperatures.

Structural and theoretical insights into solvent effects in an iron(iii) SCO complex

“…In addition to the ligand, the SCO behaviour is strongly influenced by the anion and solvent. [14][15][16][17][18][19][20] Generally, changing the anion completely alters the packing and therefore, the SCO properties. In contrast, solvent effects tend to be more subtle, with minor modifications of the lattice.…”

“…21 Since then, many studies have shown a variety of solvent effects, even in molecular materials. 18,22 In some systems SCO becomes more abrupt upon solvent exchange, [22][23][24] while in others the SCO becomes stepped or even hysteretic. 25,26 Indeed, in [Fe (tolpzph) 2 (NCS) 2 ]•THF (tolpzph = 4-p-tolyl-3-( phenyl)-5-(2-pyrazinyl)-1,2,4-triazole) it is even possible to quantitatively sense the solvent.…”

Spin-state versatility in FeII4L6 supramolecular cages with a pyridyl-hydrazone ligand scaffold modulated by solvents and counter anions

“…Dalton Transactions (10 K). 25 Garcia et al demonstrated two linear regimes between the volume of the inserted counterions and the transition temperature (T 1/2 ) of the [Fe(Rtrz) 3 ] 2+ (R = 4-amino-1,2,4triazole) one-dimensional polymer chains, i.e., when the volume is between 0.04 nm 3 and 0.09 nm 3 , T 1/2 decreases as the volume increases; when the volume exceeds 0.11 nm 3 , T 1/2 tends to saturate (∼200 K). 26 However, the influence of these two factors on SCO profiles in Fe II discrete polynuclear systems has been relatively little investigated compared to mononuclear and polymeric complexes.…”

Steric Effects on Spin States in a Series of Fe(III) Complexes

“…The solvent-dependent SCO behavior of complex 3•H 2 O can be explained based on the loss of the solvate (water in this case) due to heating the sample (Figure S17). At high temperatures, once the water molecule is removed from the crystal lattice, the structural integrity of the complex changes, affecting the magnetic properties of the SCO molecule 54 (Figure 7c).…”