The pentadentate ligands 2PyN2Q and N4Py, and their Cu(II) and Zn(II) complexes: A synthetic, spectroscopic and crystallographic structural study

Abstract

The synthesis and characterization of the new ligand N,N-bis(2-quinolylmethyl)-N-bis(2-pyridyl)methylamine (2PyN2Q), a derivative of N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine (N4Py) is reported. Purification of both N4Py and 2PyN2Q on Dowex cation exchange columns as their hydrochloride salts allowed the isolation of the byproducts N3Py and 2PyNQ, respectively. The X-ray crystal structure of [H2N4Py](PF6)2 shows that the two more basic picolyl nitrogens are protonated. X-ray structural analyses of the copper(II) complexes [Cu(N4Py)(NO3)](NO3) (1) and [Cu(2PyN2Q)(NO3)](NO3) (2) show that the binding of the nitrate ligand is influenced by the steric bulk of the quinoline rings while electrochemical studies show that the poorer basicity of the quinolinyl donors makes 2 more easily reduced than 1. X-ray structural analyses of the zinc(II) complexes [Zn(N4Py)(OH2)](CF3SO3)2·H2O (3a·H2O), [Zn(N4Py)(CH3OH)](ClO4)2·CH3OH (4·CH3OH) and [Zn(2PyN2Q)(NCCH3)](ClO4)2·CH3CN (6·CH3CN) again show that the quinoline rings have a significant influence on the way in which the monodentate ligand can bind to the zinc center. The X-ray crystal structure of [Zn(2PyNQ)2](ClO4)2 (7) is also reported. In 7 the zinc(II) ion is bonded to two pyridyl donors and one amine donor from each of two ligands and the quinolinyl donors are not bound.