Département de chimie moléculaire

The study of the magnetic properties and EPR spectra of the one-dimensional bis($μ$-chloro) Mn(II) polymer [Mn($μ$-Cl)2(bpy)]n (1) (bpy = 2,2'-bipyridine) is reported. Magnetic susceptibility measurements reveal a weak ferromagnetic interaction between the Mn(II) ions (J = +0.19 cm-1). This is the first polymer of six-coordinated Mn(II) ions with a [Mn2($μ$-Cl)2]2+ magnetic repeating unit, showing a ferromagnetic interaction. The coordination octahedra are elongated in the Cl···Cl direction and the elongation axes are parallel along the chain. Extended Hueckel calcns. show that the octahedra share an equatorial-apical edge, with the equatorial plane being parallel, and perpendicular to the Mn2($μ$-Cl)2. Due to this disposition, the overlap through the chloride bridges is small, so the antiferromagnetic contribution must also be small and, therefore, a ferromagnetic behavior is obsd. The EPR spectra of a polycryst. sample of 1 at different temps. are also reported. A variation of the bandwidth with temp. is obsd., which could be because this ferromagnetic interaction is weak: above 150 K the dipolar interaction is the predominant effect, while below 150 K the magnetic exchange interaction dominates. [on SciFinder(R)]