Complexes of ligands providing endogenous bridges. Part 4. Copper(II) complexes of macrocyclic Schiff bases derived from 2,6-diacetylpyridine and 1,n-diamino-n′-hydroxyalkanes (n,n′= 3,2; 4,2; and 5,3): synthesis, properties, and structures
The synthesis, physicochemical properties, and X-ray crystal and molecular structures of three dinuclear copper (II)complexes of tetraimine Schiff-base macrocycles derived from 2,6-diacetylpyridine and 1,n-diamino-n′-hydroxyalkanes (n,n′= 3,2; 4,2; and 5,3) are reported. The complex derived from a 20-membered macrocycle has present a single endogenous alkoxy bridge and so can serve as a speculative model for the dicopper(II) site in oxyhaemocyanin. As the ring size is increased this bridge is lost and is replaced by an unusually short hydrogen bond between the protonated and deprotonated hydroxyl groups.