The stability and photophysical properties of trivalent lanthanide complexes with 2,2Ј;6Ј,2Љ-terpyridines substituted in the 4 position (L 1 , t-butyl; L 2 , ethyl) have been compared to those with the unsubstituted ligand terpy. The stability constants log β 3 of complexes with L 1 and terpy are similar and reflect a preference for the harder heavier members of the series. Cyclic voltammetry of the [Eu(L) 3 ][ClO 4 ] 3 complexes show a considerable cathodic shift of the Eu III -Eu II reduction potential on going from terpy to L 2 and L 1 . The energy of the LMCT states, indirectly determined from the half peak potentials for ligand oxidation and europium() reduction, is too high to allow an effective non-radiative deactivation by this pathway. Complexes of the substituted ligands [Ln(L i ) 3 ][ClO 4 ] 3 (Ln = Eu or Tb) show a substantial increase in the quantum yields of the metal-centred luminescence in acetonitrile solution compared to the terpy reference systems: Q Eu = 0.10 (L 1 ), 0.11 (L 2 ) vs. 0.013 (terpy), and Q Tb = 0.67 (L 1 ), 0.34 (L 2 ) vs. 0.047 (terpy). The main factor responsible for this enhancement arises from a facilitated intersystem crossing in L 1 , L 2 and in their complexes, as demonstrated by the ratio of the fluorescence and phosphorescence intensity of both the "free" ligands and their lanthanum() tris complexes. This effect is tentatively assigned to the electron donating substituents in the 4 position affecting the mixing of energetically close singlet and triplet ligand states.

The two enantiomerically pure bridging ligands (+/-)-[ctpy-x-ctpy] have been prepared employing a two-fold stereospecific alkylation reaction of the enantiomerically pure, chiral terpyridyl-type ligands (+/-)-ctpy. The reaction of each of the enantiomerically pure bridging ligands with Fe(2+) gives rise to chiral coordination polymers whose formation and stoichiometry were followed spectrophotometrically. An assignment of the absolute configuration of the formed helical polymeric structures was carried out on the basis of circular dichroism studies. Highly ordered domains (as determined from STM imaging) of the enantiomerically pure chiral redox polymers could be prepared via the interfacial reaction, over an HOPG substrate, of the bridging ligand in CH(2)Cl(2) and FeSO(4) in water. The degree of polymerization was estimated to be up to 60 from analysis of the STM images of the highly ordered domains on HOPG. The helicality of the domains was compared to the configuration obtained from the circular dichroism studies. The electrochemical properties of the polymers were investigated using cyclic voltammetry and the results compared to those of the respective monomeric complexes. The redox behavior of the iron centers in the polymer was comparable to that of the monomeric complex [Fe((-)-ctpy)(2)](PF(6))(2) as well as to that of [Fe(tpy)(2)](PF(6))(2). The polymeric materials undergo electrodeposition following the two-electron reduction of each bridging ligand unit (one electron per terpyridine group). No ligand-mediated metal-metal interactions were evident from the cyclic voltammetric measurements, suggesting that the metal centers act independently. Moreover, oxidation of the metal centers within the polymeric materials did not give rise to electrodeposition.

The two enantiomers (Δ and Λ) of Ru(chiragen[X])Cl2, where “chiragen” is a tetradentate ligand with a chiral bridging unit between two bipyridine moieties, have been prepared in high yields. X is m-xylyl (m-xyl); other bridging groups (e.g., −(CH2)5− or −(CH2)6−) behave similarly. This complex can be used as an enantiomerically pure building block for the synthesis of stereochemically well defined polynuclear species. As an example, all three isomers (ΔΔ, ΛΛ, and ΔΛ) of [(chiragen[m-xyl])Ru(bpym)Ru(chiragen[m-xyl])](PF6)4 were prepared and fully characterized by NMR and various other spectroscopic methods.

Tetradentate ligands are obtained by joining two optically active [4,5]-pineno-2,2'-bipyridine molecules in a stereoselective reaction, where two new stereogenic centers are created. These ligands are new members of the chiragen family that form OC-6 complexes with predetermined helical chirality. Ru(II) complexes with 4,4'-dimethyl-2,2'-bipyridine occupying the remaining coordination sites have been synthesized with all three new ligands. Characterization of the ruthenium complexes by NMR spectroscopy confirm C(2)-symmetric structures in solution. CD spectra show that the complexes are composed of only one helical diastereomer with the expected absolute configurations. In addition, a strong chiral amplification is observed, if precursors of low enantiomeric purity are used. This is due to the inability of ligands that are heterochiral in the two bpy moieties to coordinate to one center. X-ray structural data were obtained for the complex Delta-[RuCG[o-xyl](4,4'-DMbpy)](PF(6))(2). Crystal data (Mo Kalpha, 298 K): trigonal, space group R3, a = 52.986(4) Å, c = 10.545(1) Å, V = 25639(4) Å(3), Z = 18, R1 = 0.087, and wR2 = 0.0986 for 2609 observed reflections.