Complexes of 6-methyl-2-pyridone with the alkaline earth metals magnesium, strontium and barium: Synthesis and structural characterisation

Reaction in dry methanol of 6-methylpyridine (Hmhp) with M(OR)2 (M = Mg, Sr, Ba) formed three new coordination compounds, with very different crystal structures. Compound [Mg4(mhp)4(MeO)4(MeOH)8] (1) forms discrete clusters containing a rare Mg4O4 cubane, only the tenth reported occurrence of such a motif. Compounds [Sr(mhp)2(Hmhp)] (2) and [Ba(mhp)2(Hmhp)(MeOH)] (3) are both eight-coordinate complexes in polymeric chains. The solvent-free 2 packs as an infinite left-handed helix with elegant sixfold screw symmetry formed as a result of twisting necessary for coordination to Sr2+ by both deprotonated nitrogen atoms. In 3 there is also a molecule of methanol coordinated to Ba2+; there is now no need for a twist to achieve the extra coordination, and so the compound forms instead a straight chain with glide-plane symmetry.