Coordination chemistry of 5,5″-disubstituted 2,2′:6′,2″-terpyridines

Two 2,2′:6′,2″-terpyridine ligands bearing substituents in the 5 and 5″-positions have been prepared and their iron(II) complexes studied to investigate the influence of substituents in these positions. A synergistic interplay between σ- and π-bonding effects, involving conjugation of the substituents with the central ring, means that, in contrast to 4′-substituted 2,2′:6′,2″-terpyridines, the metal-ligand interactions cannot be simply correlated with the electron-donor or -acceptor properties of the substituents. The crystal structure of the complex [Fe(3)₂][PF₆]₂ · 2MeCN (3=5,5″-bis(propoxy)-2,2′:6′,2″-terpyridine) is reported. In addition, cobalt(II) and ruthenium(II) complexes of 5,5″-bis(propoxy)-2,2′:6′,2″-terpyridine were prepared and characterised.