Tuning of chain chirality by interchain stacking forces and the structure–property relationship in coordination systems constructed by meridional FeIII cyanide and MnIII Schiff bases?

Dalton Transactions Pub Date: 2016-11-11 DOI: 10.1039/C6DT03222B

Abstract

We synthesized six Fe(III)–Mn(III) bimetallic compounds by self-assembling the newly developed mer-Fe cyanide PPh4[Fe(Clqpa)(CN)3]·H2O (1) and PPh4[Fe(Brqpa)(CN)3]·H2O (2) with Mn Schiff base Mn(5-Xsalen)+ cations. These compounds include [Fe(Xqpa)(CN)3][Mn(5-Ysalen)]·pMeOH·qH2O [qpaH2 = N-(quinolin-8-yl)picolinamide; salen = N,N′-ethylenebis(salicylideneiminato) dianion; X = Cl, Y = H (3); X = Cl, Y = Br (4); X = Br, Y = H (5); X = Br, Y = F (6); X = Br, Y = Cl (7); X = Br, Y = Br (8)]. When precursor 1 was used, compounds 3 and 4 were isolated to give a dinuclear entity and a linear chain structure, respectively. The reaction of precursor 2 with the Schiff bases afforded four linear Fe(III)–Mn(III) chain complexes. Chain chirality with P- and M-helicity emerges in 4, 7, and 8, while 5 exhibits chain helicity opposite to the previous chain complexes and 6 presents no chain helicity. Such a structural feature is heavily dependent on the interchain π–π contacts and the Fe precursor bridging unit. Chiral induction from a local ethylenediamine link of Y-salen is propagated over the chain via noncovalent π–π interactions. All the bimetallic compounds show antiferromagnetic interactions transmitted by the cyanide linkage. A field-induced metamagnetic transition is involved in 4, 7, and 8, while a field-induced two-step transition is evident in 6. From a magnetostructural viewpoint, the coupling constant is primarily governed by the Mn–Nax–Cax angle (ax = axial) in the bimetallic chain complexes composed of mer-Fe(III) tricyanides, although the torsion angle plays a role.

Graphical abstract: Tuning of chain chirality by interchain stacking forces and the structure–property relationship in coordination systems constructed by meridional FeIII cyanide and MnIII Schiff bases
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