Synthesis of new phenanthroline-based heteroditopic ligands -: Highly efficient and selective fluorescence sensors for copper(II) ions

The heteroditopic phenanthroline derivatives 5,6-bis(2-pyridylcarboxamido)-1,10-phenanthroline (H2L1) and 5,6-bis[(4-methoxy-2-pyridyl)carboxamido]-1,10-phenanthroline (H2L2) have been prepared and characterized, together with their luminescent ruthenium(II) complexes [Ru(bpy)(2)(H2L1,2)]-(PF6)(2) and [Ru(H2L1)(3)](PF6)(2) and the corresponding iron(II) complex [Fe(H2L1)(3)](PF6)(2). In these complexes, the metal ion is coordinated by the bidentate phen site of H2L. The luminescence of the ruthenium complexes (lambda(ex)=450 nm, lambda(em) ca. 620 nm) is completely quenched by Cu2+ ions in the micromolar concentration range and, to a lesser extent, by other metal ions. At pH 5, the response of the luminescent sensors is highly Cu2+-selective. Heterodinuclear complexes [Ru(bpy)(2)(LM)](PF6)(2), [Ru(LM)(3)](PF6)(2), and [Fe(LM)(3)](PF6)(2) have been isolated for M=Cu2+, Ni2+, Co2+, and Pd2+. It is suggested that M is coordinated to the tetradentate N4 site of L by two deprotonated amide N atoms and two pyridyl groups. This coordination type is confirmed by the EPR spectrum of the compound [Ru-II(bpy)(2)((LCuII)-Cu-1)](PF6)(2). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)