Novel self-assembled supramolecular architectures of Mn(ii) ions with a hybrid pyrazine–bipyridine ligand

Abstract

A new hybrid pyrazine–bipyridine ligand L (C₂₆H₂₀N₆) and its complexes with Mn(NO₃)₂, Mn(ClO₄)₂, MnCl₂ and MnBr₂ have been synthesised. By the self-assembly of L and Mn(II) ions three different kinds of supramolecular complexes have been obtained: binuclear baguette complex [Mn₂L(H₂O)₆](NO₃)₄·2.5H₂O 1 and tetranuclear [2 × 2] grid-type complex [Mn₄L₄](ClO₄)₈·2.5(CH₃CN)·2CH₃OH 2 and mononuclear complexes [MnL₂]X₂ (where X = Cl⁻3 and X = Br⁻4). Crystal structures and magnetic properties of Mn(II) complexes 1 and 2 have been also investigated. The crystal structures reveal that in both 1 and 2 complexes the Mn(II) ions have coordination number 6 and distorted octahedral coordination geometry. In 2 four metal cations and four ligands have assembled into a grid-type [2 × 2] array, with a perchlorate anion occupying the central cavity, with clearly a good fit for the center of the cavity. The perchlorate anion, in contrast to the nitrate anion, probably acts as a template in the formation of tetranuclear grid-type complexes. Magnetic susceptibility measurements indicate that the Mn(II) ions are all high spin, and in both 1 and 2 complexes there are weak antiferromagnetic interactions between Mn(II) ions.