Ring-size and substituent effects in relatively rigid macrocyclic quinquedentate ligands. Structure determinations of [ZnL4(H2O)2][ClO4]2·MeCN and [ZnL3(ClO4)2]

Abstract

Twenty one metal complexes of macrocyclic quinquedentate ligands with N₅-, N₃O₂-, and N₃S₂-donor sets have been isolated from cyclocondensation reactions between pyridine-2,6-dicarbaldehyde and α,ω-dianilines [e.g. 1,2-di(o-aminophenylthio)ethane] carried out in the presence of salts of bivalent transition metals. X-Ray structure analyses of [ZnL³(ClO₄)₂] and [ZnL⁴(H₂O][ClO₄]₂·MeCN(L³= 6,7-dihydro-15,19-nitrilodibenzo[e,p][1,4,7,15]-dithiadiazacycloheptadecine and L⁴= 7,8-dihydro-6H-16,20-nitrilodibenzo[f,q]-[1,5,8,16] dithiadiazacyclo-octadecine), together with spectroscopic evidence show that the 15- and 16-membered ring ligands form seven-co-ordinate complexes in which the macrocycle defines the equatorial plane of an approximate pentagonal bipyramid and the axial sites are occupied by water molecules or co-ordinated anions. The geometry of the N₃X₂-donor set (X = O or S) and hence the goodness of fit for different metal ions depends crucially on the nature of the bridge between the benzene rings in the macrocycle.