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

Abstract

Spin crossover (SCO) is very sensitive toward electronic and steric effects. The latter can lead to a distorted structure, which in turn can change the electronic properties of the complex possibly leading to a change in the spin state. Herein, we investigated the steric effects of the ligand substituents on the structure and magnetic properties of Fe(III) complexes by applying two different ligand systems. We chose the less bulky Nmethylethylenediamine and the bulkier N-phenylethylenediamine and coupled them with 3-methoxysalicylaldehyde affording HL1− HL2, while coupling with 3-ethoxysalicylaldehyde afforded HL3−HL4. Complexes [Fe(L1) 2 ]NCSe (1) and [Fe(L3) 2 ]•NCSe•H 2 O (3•H 2 O) formed with the less bulky ligand exhibit SCO behavior, while complexes [Fe(L2) 2 NCSe]•MeOH (2•MeOH), [Fe(L4) 2 NCSe] (4), and [Fe(L4) 2 NCS] ( 5) formed with the bulkier amine stay in the high-spin state. The effect of the bound anion was also investigated for complexes 4 and 5. Both experimental and theoretical methods were employed to understand the observed behavior.

The role of intermolecular interactions in [Fe(X-salEen)2]ClO4 spin crossover complexes

“…1 While early studies primarily concentrated on intramolecular factors governing spin transitions, namely coordination sphere and ligand field strength, 2,3 it has become increasingly evident that intermolecular interactions play a crucial role in the cooperative behaviour and stability of SCO complexes in the solid state. [4][5][6][7] These interactions include hydrogen bonding, [8][9][10][11] π-π stacking, [12][13][14][15] halogen bonding, [16][17][18][19] and crystal packing effects, [20][21][22][23] which can drastically impact the thermodynamic and kinetic aspects of the SCO phenomenon.…”