The new functionalized polypyridine ligands 4‘-(4-chlorophenyl)-6‘-phenyl-2,2‘-bipyridine (clpbpy), 4‘-(4-tolyl)-6‘-phenyl-2,2‘-bipyridine (tpbpy), and 4‘-(4-carboxyphenyl)-6‘-phenyl-2,2‘-bipyridine (cpbpy), together with the known 4‘-(4-hydroxyphenyl)-6‘-phenyl-2,2‘-bipyridine (hpbpy) and 4‘-(4-tolyl)-2,2‘:6‘,2‘ ‘-terpyridine (ttpy) have been used to prepare a new series of Ir(III) cyclometalated compounds [Ir(ppy)2(HL-X)][PF6] (ppy is the monoanion of 2-phenylpyridine; HL-X = hpbpy (1), clpbpy (2), tpbpy (3), cpbpy (4), and ttpy (5)). All the new species have been characterized by IR and 1H NMR, and the crystal structure of 4 is also presented and discussed. All the metal complexes exhibit oxidation mainly centered on an orbital derived from an Ir−(C-) σ-bond and ligand-centered reduction processes; all of them are luminescent from 3MLCT levels both at 77 K in a rigid matrix and at 298 K in fluid solution. The redox and absorption properties are more or less insensitive to the remote substituents on the rotationally free 4‘-phenyl ring, whereas fine-tuning of the luminescence properties is observed on changing substituents. The results show that the “energy gap law” for radiationless decay in the weak coupling limit is obeyed by this series of complexes, when complex 5 is excluded. Interestingly, the slope of the linear relationship between ln k nr and the emission energy at room temperature is significantly smoother than that reported for other luminescent polypyridine complexes containing different metals. Because of the high luminescence quantum yield and the presence of functionalities in the polypyridine ligand framework, the complexes reported may be considered as useful building blocks for light- and redox-active, multicomponent supramolecular systems.

The photophysical and electrochemical properties of a series of cationic cyclometalated Ir(III) complexes is reported. The complexes are of general formula [Ir(ppy)2(R,R‘-bpy)]+(1−5; PF6 - as counterion) where ppy = 2-phenylpyridinato anion. Complexes 1−3 contain asymmetric bpy ligands with R and R‘ substituents in the 6‘ and 4‘ positions, while complexes 4 and 5 bear bpy ligands symmetrically substituted in the 4 and 4‘ positions. Complex 5 was structurally characterized by single-crystal X-ray crystallography, revealing a cis arrangement of the metalated C atoms of the ppy ligands. All the species exhibit strong absorption in the UV region, due to spin-allowed ligand-centered (LC) transitions, and moderately intense bands in the visible region, due to charge transfer (CT) transitions. Several redox processes have been evidenced in each complex and assigned to specific components. The complexes also exhibit relatively strong and long-lived (from 10-8 to 10-5 s, depending on temperature and matrix) luminescence, in all the experimental conditions used (acetonitrile solution and spin-coated films at 298 K; butyronitrile rigid matrix at 77 K). The substituents of the polypyridine ligands affect in a substantial way the redox and photophysical properties of the compounds. In particular, a phenyl substituent on the polypyridine chelating ligand in the 6‘ position (complexes 1−3) stabilizes oxidation of an orbital which receives significant contributions from the ppy ligands and leads to emission from triplet ligand-to-ligand charge transfer (LLCT) excited states. When such a phenyl is absent in the ligand structure (complexes 4 and 5), the usual triplet metal-to-ligand charge transfer (MLCT) emission predominates.

Two new heteroleptic pentacoordinated Zn(II) complexes (1 and 2) containing 4,4 0 -disubstituted 2,2 0bipyridines as the main ligand and curcumin (curc) as an ancillary ligand have been synthesized, spectroscopically and structurally characterized, and tested in vitro towards different human cancer cell lines. While the nitrogen ligands are almost inactive, Zn(II) curc derivatives 1 and 2 show promising and selective anticancer properties. In particular the curc Zn(II) complex 1 shows the strongest growth inhibition in all cell lines, being even more effective than the pure curc in the LAN-5 neuroblastoma cell line. Furthermore, the curc moiety makes the complexes 1 and 2 fluorescent, a feature enabling investigation of their interaction with DNA through a new optical method previously tested with the reference fluorescent intercalator ethidium bromide. This analysis demonstrates that the interaction mode of curc, 1 and 2 with DNA in the double helix favors their alignment perpendicular to the DNA axis, suggesting a partial inter-base intercalation of these Zn(II) complexes.

Cyclometallated chloridoplatinum complexes containing neutral monodentate ligands such as 2‐phenylpyridine (1a), 2‐(2′‐thienyl)pyridine (1c) or 4‐methoxypyridine (1d), as well as the cyclometallated benzo[h]quinoline chlorido complex with 4‐methoxypyridine (2d), can be synthesised in a few minutes by irradiating the reaction mixture with microwaves. The single‐crystal X‐ray molecular structures of the solvato complexes 1·dmso and 2·dmso as well as 1c, 1d and 2d are reported. The availability of this class of complexes in a few minutes offers the possibility of a combinatorial approach for the preparation of libraries of homologous compounds of potential interest for applicative purposes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Tris-beta-diketonate lanthanide(III) complexes (Ln = Eu, Er, Yb, Tb), of general formula [Ln(acac)3 L(m)], with chelating ligands such as 4,7-disubstituted-1,10-phenanthrolines and 4,4'-disubstituted-2,2'-bipyridines, have been synthesized and fully characterized. The inductive effects of the para-substituents on the aromatic N-donor ligands have been investigated both in the solid and in the solution states. Single-crystal X-ray structures have been determined for the diethyl 1,10-phenanthroline-4,7-dicarboxylate europium and 4,4'-dimethoxy-2,2'-bipyridine erbium derivatives, revealing a distorted square antiprismatic geometry around the lanthanide atom in both cases. The influence exerted by the p,p'-substituents with respect to the nitrogen coordinating atoms on the Ln-N bond distances is discussed comparing the geometrical parameters with those found for the crystal structures containing the fragments [Ln(III)(phen)] and [Ln(III)(bipy)] obtained from the Cambridge Structural Database. The influence exerted by the electron-attracting groups on the coordination ability of the ligands, that in some cases becomes lack of coordination of the lanthanide ions, has been also detected in solution where the loss of the ligand has been followed by UV-vis spectroscopy. Moreover, the use of relatively long alkoxy chains as substituents on the 1,10-phenanthroline ligand led to the formation of a promesogenic lanthanide complex, whose thermal behavior is encouraging for the synthesis of new lanthanide liquid-crystalline species.

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New Zn(II)-curcumin based heteroleptic complexes (1-5) have been synthesized and fully characterized, with the aim to improve the bioactivity of the precursor derivative [(bpy-9)Zn(curc)Cl] (A), a potentially intercalating antitumor agent recently reported. Some structural changes have been made starting from the reference complex A, in order to introduce new functionalities, such as electrostatic and/or covalent interactions. In particular, keeping the same N,N chelating ligand, namely bpy-9, two completely different Zn(II) species have been obtained: a tetracoordinated Zn(II) cation with tetrafluoroborate as counterion (1) and a dimeric neutral complex in which the sulfate anion acts as a bridging group through two Zn(II) centres (2). Moreover, by changing the N,N chelating unit, [(L(n))Zn(curc)Cl] complexes (3-5), in which the Zn(II) ion shows the same pentacoordination seen in the precursor complex A, have been obtained. The antitumour activity of all new Zn(II) complexes was tested in vitro against the human neuroblastoma cell line SH-SY5Y in a biohybrid membrane system and the results indicate that all species exhibit strong cytotoxic activity. In particular the ionic tetrafluoroborate Zn(II) complex, 1, and the neutral phenanthroline based Zn(II) derivative, 4, show the strongest growth inhibition, being even more effective than the model complex A. Both complexes have a dose-dependent anti-proliferative effect on cells as demonstrated by the decrease of viability and the increase of Annexin V and PI-positive cells with the increase of their concentration. Cells treated with complexes 1 and 4 undergo apoptosis that involves the activation of JNK, caspase 3 and MMP changes. Finally, complex 1 is more effective in the induction of caspase-3 activation demonstrating its ability to trigger the execution-phase of cell apoptosis.