Seven-co-ordination in metal complexes of quinquedentate macrocyclic ligands. Part 6. Magnesium complexes of macrocyclic ligands containing nitrogen and oxygen donor atoms

Abstract

Reaction of 2,6-diacetylpyridine or 2,6-diformylpyridine with 3,6-dioxaoctane-1,8-diamine in methanol in the presence of MgCl₂·6H₂O gves complexes [MgL(OH₂)₂]Cl₂·H₂O of 15-membered quinquedentate N₂O₂ macrocycles (L) in high yield. Simple metathetical reactions lead to derivatives containing other anions including neutral complexes having axially co-ordinated thiocyanate. On the basis of various physical properties, the complexes are assigned seven-co-ordinate, probably pentagonal-bipyramidal, structures. Control experiments show that in the absence of a salt of Mg²⁺ the macrocycles are formed in only small yield or not at all. The Ca²⁺ ion is ineffective in oromotina the synthesis of these macrocvcles, as is Mg²⁺ in the synthesis of three related quadridentate N₄ and N₃O macrocycles.