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

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.