Study of Spin Crossover Property of a Series of X‐OMe‐SalEen (X=6, 5 and 4) Based Fe(III) Complexes

Abstract

Three complexes bearing the molecular formula [Fe(X‐OMe‐SalEen)2]NCY⋅nH2O; X=6, Y=S, n=0 (1); X=5, Y=S, n=1.5 H2O (2) and X=4, Y=Se, n=0 (3), where 6‐OMe‐SalEen=2‐((E)‐(2‐(ethylamino)ethylimino)methyl)‐6‐methoxyphenol, 5‐OMe‐SalEen=2‐((E)‐(2‐(ethylamino)ethylimino)methyl)‐5‐methoxyphenol, and 4‐OMe‐SalEen=2‐((E)‐(2‐(ethylamino)ethylimino)methyl)‐4‐methoxyphenol, have been synthesized, characterized and their spin crossover behavior has been studied. The ligands differ in the position of the methoxy group (ortho, meta, and para) of the phenoxide ring directly bonded to the Fe center. Complex 1 and 3 comprise FeIII centers, whereas rare crystallographically independent high‐spin and low‐spin FeIII centers are present in complex 2. Complex 1 shows a sharp and hysteric spin crossover behavior with a hysteresis loop having 4 K width. Complex 2 shows spin crossover for the FeIIILS in solvated form which after desolvation becomes stable at the high spin. Complex 3 shows abrupt and incomplete spin crossover above room temperature. Magneto‐structural correlation and UV‐Vis spectroscopy have been done to study spin‐crossover behavior and the spin transition temperature of the complexes.

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

“…Two or more peaks can be observed for all the three complexes, one ranging from 300 to 450 nm and the others ranging from 450 to 800 nm. The peak below 400 nm is due to the π–π* transition of the ligand. , Complex 2 , which has no substituent, exhibits a λ max of 331 nm for the π–π* transition. In 1 , the mesomeric effect of the methoxy group (OMe) reduces the π–π* energy gap, leading to a bathochromic effect (λ max = 354 nm).…”

“…Thermogravimetric measurements were carried out for 1 – 3 , and the data are provided in Figure S14. It was found that 3 is thermally very stable, with a decomposition temperature of 448 K. ,,,, This type of thermally stable SCO molecule with a high transition temperature (366 K) can be used to prepare magnetic switches and devices for high-temperature applications.…”

“…The peak below 400 nm is due to the π–π* transition of the ligand. 20 , 33 Complex 2 , which has no substituent, exhibits a λ max of 331 nm for the π–π* transition. In 1 , the mesomeric effect of the methoxy group (OMe) reduces the π–π* energy gap, leading to a bathochromic effect (λ max = 354 nm).…”

Effect of intermolecular anionic interactions on spin crossover of two triple-stranded dinuclear Fe(ii) complexes showing above room temperature spin transition

“…The SCO behavior is greatly influenced by various factors such as counter anion, ligand field strength, and solvent mole-cules present in the crystal lattice. [36][37][38][39][40] Our group reported a series of complexes [Fe(5-X-SalEen) 2 ]NCS (X = Me, Br, OMe and 5-X-SalEen = condensation product of 5-substituted salicylaldehyde and N-ethylethylenediamine) and showed that with increasing ligand field strength the spin transition became more abrupt and T 1/2 shifted towards the higher temperature. 36 Pfrunder et al studied the SCO properties of [Co(terpy) 2 ] 2+ (terpy = terpyridine) complex cation under different anionic environment made up of 1,3-diiodotetrafluorobenzene (1,3-DITFB) or 1,3,5-triiodotrifluorobenzene (1,3,5-TITFB) anions.…”

“…The SCO behavior is greatly influenced by various factors such as counter anion, ligand field strength, and solvent molecules present in the crystal lattice. 36–40 Our group reported a series of complexes [Fe(5-X-SalEen) 2 ]NCS (X = Me, Br, OMe and 5-X-SalEen = condensation product of 5-substituted salicylaldehyde and N -ethylethylenediamine) and showed that with increasing ligand field strength the spin transition became more abrupt and T 1/2 shifted towards the higher temperature. 36…”