Preparation and characterization of cobalt(II), nickel(II) and copper(II) complexes with water-soluble macrocyclic N 4-ligands: 6,15-diethyl-4,13-dihydro-1,10-dimethyl-( E)-dipyridinio [b,i] [1,4,8,11] tetraazacyclotetradecine iodide or methyl sulfate

Abstract

The mixture of 6,15-diethyl-4,13-dihydro-( E)-dipyrido [b,i] [1,4,8,11] tetraazacyclotetradecine ( 2-E) and 6,15-diethyl-4,13-dihydro-( Z)-dipyrido [b,i][1,4,8,11] tetraazacyclotetradecine ( 2-Z) was prepared by cyclization of 3,4-diaminopyridine and 2-ethyl-3-ethoxyacrolein. Two kinds of isomers were separated by repeated recrystallization from chloroform. Methylation of pyridine comprised in 2-E using iodomethane or dimethyl sulfate afforded the corresponding dimethylated product ( 2-E-I or 2-E-S), which is soluble in water. The cobalt(II), nickel(II) and copper(II) complexes of 2-E-I and 2-E-S were prepared. The absorption bands appearing in the energy range greater than 18 000 cm −1 were attributed to the π → π* transitions within a ligand molecule and CT transitions from metal to ligand. Since the d → d* bands for nickel(II) and copper(II) complexes were obscured by the π → π* and CT bands, no significant absorption bands were found in the region more than 18000 cm −1. One of the d → d* bands for the cobalt(II) complex was observed at around 13 000 cm −1. These complexes assume the square- planar structures. A strong IR band due to the CN stretching mode of the macrocycle moiety was observed at ca. 1640 cm −1 and shifted slightly toward lower energy upon metal-coordination, cis ( 2-Z) and trans ( 2-E) isomers in the present macrocycle can be judged by the amine proton signals of NMR spectra. All proton signals except for amine protons show downfield shifts due to the deshielding effect of the positive charge provided by methylation of pyridine contained in the metal-free macrocycle. Upon formation of the nickel(II) complex all proton signals, except the aromatic protons adjacent to the nitrogen atom of a pyridine ring, also show a downfield shift, which is attributed to the deshielding effect based on the positive charge given by nickel(II). The intensity change of the electronic spectrum at 425 nm is available for the determination of copper(II) concentrations in the aqueous solution using the water-soluble macrocycles ( 2-E-I and 2-E-S) and a good linear correlation is observed up to 8 × 10 −6 mol dm −3.