Methyl group influence on the formation of CuI complexes with thio-pyridine ligands

In order to investigate the effect of methyl group substitution adjacent to a pyridyl N donor, three ligands were synthesised and complexed with CuI in a 1:2 ratio. The crystal structures of three CuI complexes were determined. The dimethylated ligand bis(6-methyl-2-pyridylmethyl)sulfide (L¹) gave rise to a tetranuclear complex with two Cu₂I₂ bridges in which the Cu centres were four-coordinate. The asymmetric ligand 2-(6-methylpyridyl)methyl(2-pyridyl)methylsulfide (L²) gave a tetranuclear complex which contained two parallel Cu₂I₂ bridges. In each Cu₂I₂ bridge, one Cu centre was three- and the other four-coordinate. In contrast, the ligand bis(2-pyridylmethyl)sulfide (L³), with no Me substitution, gave rise to a one-dimensional coordination polymer with CuI chains. It was found that the differences in the complexes were a result of both the electronic and steric effects arising from the Me substitution of the pyridine donors and that no one effect completely dominated.