Divalent transition metal(II) complexes of two heterocyclic ligands with pendant pyridinyl groups: Synthesis, characterization and electrochemistry

Treatment of the pentadentate macrocyclic ligand 4-(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane, L, and the hexadentate macrocyclic ligand 4,10-bis(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane, L′, with one equivalent of a M2+ metal salt (M = Co, Ni, Cu) in methanol yielded six mononuclear complexes, [CoL(MeCN)](ClO4)2 (1), [NiL(H2O)]Cl2 (2), [CuL(MeCN)](ClO4)2 (3) and [ML′](ClO4)2 (4–6). Their solid state crystal structures were determined using X-ray single crystal diffraction analysis. In complexes 1–3, the metal centres exhibit a slightly distorted octahedral geometry, resulting from the coordination of three nitrogen and two sulfur donating atoms in the ligand L and one solvent molecule (MeCN for complexes 1 and 3, water for complex 2) whereas in complexes 4–6, the coordination around the metal centres was satisfied by four nitrogen and two sulfur atoms from the ligand L′. The electronic spectra and electrochemistry of these complexes are reported.

Graphical abstractThe complexes of two macrocyclic ligands L and L′ with Co2+, Ni2+ and Cu2+ adopt similar structures (L = 4-(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane; L′ = 4,10-bis(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane). The additional pyridinyl group in the ligand L′ improves the reversibility of the reduction processes of its transition metal complexes due to the nature of its σ-donor and π-acceptor properties in these complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide