Phosphonate-functionalized heteroleptic ruthenium(II) bis(2,2':6',2''-terpyridine) complexes

The heteroleptic complexes [Ru(1)(4)][PF6]2, [Ru(2)(4)][PF6]2, [Ru(Phtpy)(4)][PF6]2, and [Ru(pytpy)(4)][PF6]2 (Phtpy = 4′-phenyl-2,2′:6′,2″-terpyridine, pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, 1 and 2 = 4-methyl ester substituted derivatives of Phtpy and pytpy, 4 = ethyl 2,2′:6′,2″-terpyridine-4′-phosphonate) have been prepared. The single crystal structure of ligand 1 (1 = methyl 4-carboxy-4′-phenyl-2,2′:6′,2″-terpyridine) is reported. The introduction of the 4-methyl ester group causes a small red shift in the MLCT band of the ruthenium(II) complexes and a small shift to a more positive potential for the Ru2+/Ru3+ couple. The new complexes should serve as a useful starting point for development of ruthenium(II) dyes suited for sensitization of p-type semiconductors.