Cyanide-Bridged Mn(III)−Fe(III) Bimetallic Complexes Based on the Pentacyano(1-methylimidazole)ferrate(III) Building Block:  Structure and Magnetic Characterizations

Abstract

Seven cyanide-bridged bimetallic complexes have been synthesized by the reaction of [Fe(1-CH3im)(CN)5]2- with Mn(III) Schiff base complexes. Their crystal structure and magnetic properties have been characterized. Five complexes, [Mn2(5-Brsalen)2Fe(CN)5(1-CH3im)] x H2O (1), [Mn2(5-Clsalen)2(H2O)2Fe(CN)5(1-CH3im)] x H2O (2), [Mn2(5-Clsaltn)2(H2O)2Fe(CN)5(1-CH3im)] (3), [Mn2(5-Clsaltmen)2(H2O)2Fe(CN)5(1-CH3im)] x H2O (4), and [Mn2(5-Brsaltmen)2(H2O)2Fe(CN)5(1-CH3im)] x CH3OH (5), are neutral and trinuclear with two [Mn(SB)]+ (SB2- = Schiff base ligands) and one [Fe(1-CH3im)(CN)5]2-. Complex {[Et4N][Mn(acacen)Fe(CN)5(1-CH3im)]}n x 6nH2O (6) is one-dimensional with alternate [Mn(acacen)]+ and [Fe(CN)5(1-CH3im)]2- units. The two-dimensional complex {[Mn4(saltmen)4Fe(CN)5(1-CH3im)]}n[ClO4]2n x 9nH2O (7) consists of Mn4Fe units which are further connected by the phenoxo oxygen atoms. Magnetic studies show the presence of ferromagnetic Mn(III)-Fe(III) coupling in the trinuclear compounds with the magnetic coupling constant (J) ranging from 4.5 to 6.0 cm-1, based on the Hamiltonian H = -2JSFe(SMn(1) + SMn(2)). Antiferromagnetic interaction has been observed in complex 6, whereas ferromagnetic coupling occurs in complex 7. Complexes 6 and 7 exhibit long-range magnetic ordering with a TN value of 4.0 K for 6 and Tc of 4.8 K for 7. Complex 6 shows metamagnetic behavior at 2 K, and complex 7 possesses a hysteresis loop with a coercive field of 500 Oe, typical of a soft ferromagnet.

Solely μ1,1-azido-bridged heterometallic compound

“…Moreover, the magnetization values blow 10 kOe are low, further proving the presence of intermolecular magnetic interaction. Similar situations occur to other Mn(III)-containing high-spin polynuclear compounds [15]. DFT calculations and the experimental observations have shown that end-on doubly azide-bridged symmetric Cu 2 dimer should exhibit ferromagnetic coupling with Cu-N-Cu bond angles below 104°and antiferomagnetic larger than 104° [13].…”

“…DFT calculations and the experimental observations have shown that end-on doubly azide-bridged symmetric Cu 2 dimer should exhibit ferromagnetic coupling with Cu-N-Cu bond angles below 104°and antiferomagnetic larger than 104° [13]. The bridging Cu-N-Cu bond angle of 102.68 (15)°in complex 1 lies below 104°, and thus ferromagnetic CuÁ Á ÁCu coupling is anticipated. The J CuCu value is comparable to that of complexes with similar Cu 2 (l 1,1 -N 3 ) 2 structural motif [11b,14].…”

Magnetic assemblies based on Mn(III) salen analogues

“…The presence of the tunneling relaxation readily explained the reduction of the energy barrier from Δ = |D ST |(S 2 T − 1/4) = 17.4 cm −1 (theoretical value) to 9.7 cm −1 (observed value). [116]. In all these compounds, [Mn III (SB)] + is capped by a water molecule forming discrete structures.…”

“…This symmetrical pentanuclear unit interacts with four neighboring units by forming an out-of-plane dimeric moiety in the [Mn III (saltmen)] + moieties as shown in Section 4, consequently constructing a 2D network having a dodecanuclear [ Mn III (O Ph ) 2 Mn III NC Fe III CN ] 4 cyclic repeat unit. Therefore, the Mn(III) ion has a distorted square bipyramidal geometry, in which the two apical sites are occupied by the nitrogen atom from [Fe III (CN) 6 [116]. The dc magnetic measurements displayed similar magnetic properties (J = 2.34(7) cm −1 , g = 2.04(2), zJ = 0.036(4) cm −1 ) exhibiting a long-range order at T c = 4.8 K.…”

“…One-dimensional chain structure of (NEt 4 )[{Mn III (acacen)}{Fe III (CN)5 (1-CH 3 im)}]·6H 2 O. Reproduced with permission from Ref [116]…”