Fe(III) salEen derived Schiff base complexes as potential contrast agents

Unusual Magneto‐Structural Features of the Halo‐Substituted Materials [FeIII(5‐X‐salMeen)2]Y: a Cooperative [HS‐HS]↔[HS‐LS] Spin Transition

“…[33] The object of this work is to revisit the [Fe III (X-salRen) 2 ]Y spin-crossover family [24,26] that originated in the 1970s and extend it with freshly designed members that have the potential to exhibit previously unobserved rare magnetic behaviour. In the course of this investigation, some aspects of our work coincided with the research conducted by Martinho et al [4,[31][32][33] Herein we present areport on as ystematic study of spin-crossover features within the series of halo-substituted complexes [Fe III (5-X-salMeen) 2 ]Y (X = F, Cl, Br and I; Y= ClO 4 and BPh 4 ). Previously,W ilson and Sinn along with their co-workers demonstrated magnetically and crystallographically the influence of electronic properties of substituent groups on thes pin states of the compounds in the series [Fe III (X-salMeen) 2 ]PF 6 (X = 5-OMe, 3-OMe and 5-NO 2 ).…”

“…The object of this work is to revisit the [Fe III (X‐salRen) 2 ]Y spin‐crossover family that originated in the 1970s and extend it with freshly designed members that have the potential to exhibit previously unobserved rare magnetic behaviour. In the course of this investigation, some aspects of our work coincided with the research conducted by Martinho et al . Herein we present a report on a systematic study of spin‐crossover features within the series of halo‐substituted complexes [Fe III (5‐X‐salMeen) 2 ]Y (X=F, Cl, Br and I; Y=ClO 4 and BPh 4 ).…”

“…[Fe III (5‐Br‐ salEen) 2 ]Cl ⋅ 0.5 H 2 O exists at 150 K as two independent complex cations in the crystallographic asymmetric unit: one in the HS state and the other in the LS state, a magnetic feature not crystallographically observed previously in this system. However, structural evidence of such [HS‐LS] coexistence has been reported for a mere handful of other types of iron(III)‐based SCO complexes, generally those whose spin transition exhibits a [HS‐LS] plateau. Unfortunately, room‐temperature magnetic and crystallographic data on [Fe III (5‐Br‐ salEen) 2 ]Cl ⋅ 0.5 H 2 O are not available, nor a spin‐transition curve for this compound.…”

“…However, structural evidence of such [HS‐LS] coexistence has been reported for a mere handful of other types of iron(III)‐based SCO complexes, generally those whose spin transition exhibits a [HS‐LS] plateau. Unfortunately, room‐temperature magnetic and crystallographic data on [Fe III (5‐Br‐ salEen) 2 ]Cl ⋅ 0.5 H 2 O are not available, nor a spin‐transition curve for this compound. [Fe III (5‐Br‐salEen) 2 ]ClO 4 exhibits polymorphism induced by the crystallization conditions.…”

“…[29] Modulation of spin-crossover properties in iron(III)-salicylaldimine systemsb yi ntroducing halogen substituents into the para position of the phenolate moiety has been demonstrated spectacularly by the complexes [Fe(qsal-5-X) 2 ]Y (qsal = quinolylsalicylaldiminate;X = halogen;Y = counter anion). [6,7,11,18,30] Within the family [Fe III (R 1 ,R 2 -salRen) 2 ]Y,o nly three crystallographically characterized 5-halo-substituted members are known,n amely [Fe III (5-Br-salEen) 2 ]Cl·0.5 H 2 O, [31] [Fe III (5-Br-salEen) 2 ]ClO 4 [4,32] and [Fe III (5-I-salEen) 2 ]ClO 4 . [33] [Fe III (5-Br-salEen) 2 ]Cl·0.5 H 2 Oe xists at 150 Ka st wo independent complex cations in the crystallographic asymmetricu nit:o ne in the HS state and the other in the LS state, am agnetic feature not crystallographically observed previously in this system.…”