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

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.