Bimetallic cyanido-bridged magnetic materials derived from manganese(iii) Schiff-base complexes and pentacyanidonitrosylferrate(ii) precursor

Abstract

Three heterobimetallic Mn^IIIFe^II complexes: [Mn(5-Br-salpn)(H₂O)]₂[Fe(CN)₅NO]·2H₂O (1), [{Mn(salen)}₂Fe(CN)₅NO]·2H₂O (2) and [{Mn(saltmen)}₄Fe(CN)₅NO](ClO₄)₂·H₂O·2CH₃OH (3), have been synthesized by the reactions of Mn^III/Schiff–base (SB) complexes, [Mn(SB)(H₂O)]⁺, (SB being salen²⁻ = N,N′-ethylenebis(salicylideneiminato) dianion; 5-Br-salpn²⁻ = N,N′-1,3-propylenebis(5-bromosalicylideneiminato) dianion or saltmen²⁻ = N,N′-(1,1,2,2-tetramethylethylene) bis(salicylideneiminato) dianion) with the [Fe(CN)₅NO]²⁻ building block. X-Ray diffraction analyses on single crystals reveal that 1 has a trinuclear molecular structure, 2 displays a two-dimensional (2D) network structure, and 3 possesses a new 2D network of Mn^III dinuclear motifs. The magnetic measurements show that the interaction between the Mn^IIIS = 2 spins through the [NC–Fe–CN] bridges is systematically of antiferromagnetic nature: J/k_B = −0.95(5) K and J/k_B = −1.15(5) K for 1 and 2, respectively, while the direct Mn^III–Mn^III interaction, in the {Mn₂(saltmen)₂} dinuclear units present in 3, is ferromagnetic with J/k_B = +1.75(5) K. Due to the S_T = 4 spin ground state of these dinuclear units and the uniaxial magnetic anisotropy brought by the Mn(III) metal ions, 3 exhibits single-molecule magnet properties. The 400–900 nm optical properties of the three compounds have been also investigated, showing no significant photoactivity unlike in the Na₂[Fe(CN)₅NO] precursor.