Structural effects of potentially hexadentate N4O2, N4S2 or N6 ligands involving pyridine, amine and ether or thioether donors: crystal structure of copper(II) and zinc(II) complexes †

Abstract

The two new hexadentate ligands 1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado) and 1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt), have been synthesized as their tetrahydrochloride salts and their protonation constants and the stability constants of the copper(II) and zinc(II) chelates determined by potentiometry. The formation of M(HL) and ML species was detected in all cases except for pydado which gives only ZnL species. The two central donor atoms (ether oxygen or thioether sulfur) of the ligands do not have a great influence on the protonation constants, but the stability constants of copper(II) complexes with pydadt are slightly greater than those of pydado. The solid copper(II) and zinc(II) complexes have been prepared as their perchlorate salts. The crystal structures of four complexes are reported. In all the zinc(II) complexes the metal center is encapsulated by the ligand in a distorted octahedral environment, whereas the copper(II) complex with pydado is a four-coordinated compound. The copper(II) complexes have been examined by ESR, electronic spectroscopy and cyclic voltammetry to show the effects of the two central donor atoms on the structure and properties.