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.

The synthesis and characterization of a novel series of tetrachlorocuprate salts, based on N-alkylpyridinium cations ([Cn−Py]+), are described. The [Cn−Py]2[CuCl4] salts (n = 6, 9−18) were found to be crystalline solids except for the short-chain homologues (n = 6, 9, 10), which were obtained as viscous liquids. X-ray powder diffraction measurements showed that in the crystalline state the ionic species give rise to layered structures. An X-ray crystal structure study of [C15−Py]2[CuCl4] also confirmed the lamellar packing and revealed the monolayer type of organization with strong interdigitation and canting of N-alkyl chains. Most solid salts (n ≥ 12) are thermotropic liquid crystals, with hexagonal columnar, cubic, and smectic phases appearing in the order of increasing chain length and/or temperature. This unique phase behavior has been undoubtedly proved by optical, calorimetric, and diffractometric techniques. The details of the structural organization in both the columnar and cubic phases are not entirely defined yet.

Two homologous series of N-alkylpyridinium salts, [Cn-Py] 2 [PdX 4 ] (n ) 12, 14, 16, 18; X ) Cl, Br), have been synthesized, and their thermal behavior has been studied by differential scanning calorimetry and hot-stage polarizing optical microscopy. Except for the substances with n ) 12, all the materials show thermotropic polymorphism. The crystal structures of, and [C16-Py] 2 [PdBr 4 ] have been solved. All three complex salts crystallize in the triclinic space group P1 h. Crystal packing reveals layered structures with alternating polar and apolar sublayers, where each [PdX 4 ] 2anion is sandwiched between two antiparallel pyridinium cations. Alkyl chains are highly interdigitated and tilted with respect to the layer normal. The structural characterization of the [Cn-Py] 2 -[PdX 4 ] (n ) 16, 18; X ) Cl, Br) salts has been achieved also through variable-temperature powder X-ray diffraction. The [PdCl 4 ] 2salts undergo transitions to a second crystalline phase and then to an ordered and a disordered smectic phase. The latter are assigned to single-layered smectic-E and partially bilayered smectic-A d phases, respectively. On warming, the [PdBr 4 ] 2analogues only show the smectic-A d phase, preceded by a crystalline phase very similar to the room-temperature solid phase. The relative importance of hydrogen bonding throughout the sequence of structural changes is briefly addressed.