Insensitivity of Magnetic Coupling to Ligand Substitution in a Series of Tetraoxolene Radical-Bridged Fe₂Complexes

Abstract

The elucidation of magnetostructural correlations between bridging ligand substitution and strength of magnetic coupling is essential to the development of high-temperature molecule-based magnetic materials. Toward this end, we report the series of tetraoxolene-bridged Fe II 2

Enhancing Magnetic Communication between Metal Centres: The Role of s‐Tetrazine Based Radicals as Ligands

“…For example, when o ‐benzosemiquinone is functionalized with electron‐withdrawing groups such as halogens or aryl rings, the electron density on the oxygen atoms is decreased, weakening the coupling. On the other hand, when electron‐donating groups such as tert ‐butyl are attached to the radical, stronger exchange is observed [11] . Furthermore, when nitrogen donor atoms are included in the substituents (e.g.…”

Electronic Lability of Quinonoid‐Bridged Dinuclear 3 d‐Metal Complexes with Tetradentate N‐Donor Bases

“…Recently a paper issued, devoted to the elucidation of effect of the substituents in the tetraoxolene bridge on the nature and strength of exchange interactions in a series of Fe(II) complexes [Fe 2 ( Me 3 TPA ) 2 ( X DHBQ m − )] n+ (m=2, n=2: X=OMe, Cl, NO 2 ; m=0, n=4: X=SMe 2 ; Me 3 TPA =tris(6‐methyl‐2‐pyridylmethyl)amine) and the radical‐bridged analogues [Fe 2 ( Me 3 TPA ) 2 ( X DHBQ m − )] n+ (m=3, n=1: X=OMe, Cl, NO 2 ; m=1, n=3: X=SMe 2 ) (Scheme 9). [48] The minimal effects of substituents in the 3‐ and 6‐positions of X DHBQ m − on the magnetic coupling strength is caused by negligible spin density on the substituents and neighboring C atoms. Studied complexes are SMMs, with relaxation barriers of U eff =50, 41, 38, and 33 cm −1 for X=OMe, Cl, NO 2 , and SMe 2 , respectively.…”

Semiquinone radical-bridged M2 (M = Fe, Co, Ni) complexes with strong magnetic exchange giving rise to slow magnetic relaxation

“…3 Plots of the molar magnetic susceptibility times temperature (c M T) versus T for 1-3 (top) and 4-6 (bottom) under an applied field of 1 T. Solid lines indicate fits to the data using eqn (1) for 1-3, eqn (2) for 4 and 5, and a giant spin approximation with S ¼ 3/2 for 6, as described in the text. Table 3 Zero-field splitting parameters and corresponding calculated spin reversal barriers (U calc ) compared with experimental spin reversal barriers (U eff ) extracted from dynamic magnetic data for semiquinone-bridged compounds 4 (M ¼ Fe), 5 (M ¼ Co), and 6 (M ¼ Ni) bis(bidentate) 2,5-dihydroxy-1,4-benzoquinone derivatives with Fe (J ¼ À57 to À65 cm À1 ) 20 and Co (J ¼ À52 cm À1 ). 15 Likely, this prominent difference results predominantly from the delocalization of the unpaired electron over only two O atoms in semiquinone versus four in the bis(bidentate) analogues.…”

“…Our results support a growing number of studies that demonstrate the utility of judiciously selected multinuclear single-molecule magnets featuring radical-bridged, high-anisotropy metal ions for suppressing through-barrier relaxation processes. [17][18][19][20]…”

“…For instance, 2,5-disubstituted semiquinone derivatives, which can act as bis(bidentate) bridging ligands (Scheme 1, bottom), 11,12 have been employed to synthesize radical-bridged dinuclear complexes exhibiting strong magnetic exchange coupling [13][14][15][16] and in some cases single-molecule magnet behavior. [17][18][19][20] In contrast, magnetic coupling involving the bis(monodentate) benzosemiquinone molecule (Scheme 1, top) has not been reported.…”