No abstract

Luminescent metal complexes are key materials for several applications such as lighting, analytical probes, and lasers. In many cases compounds based on precious (i.e. platinum group) and rare earth metals are utilized, which are often rather expensive and environmentally problematic. In recent years, interest is growing in luminescent complexes based on less traditional but more abundant and cheaper metal elements. In this scenario compounds of metals with a d10 electronic configuration are playing a prominent role, also thanks to the versatility of their luminescent levels which can be of ligand centred, charge transfer or, in the case of polynuclear compounds, even metal-centred nature. Here we focus on some selected examples of Cu(I), Ag(I), Au(I), Zn(II) and Cd(II) luminescent complexes to suggest some possible routes towards promising and unprecedented emitting materials.

The photophysical properties of a series of charged biscyclometalated [Ir(ppy)(2)(N^N)](1+) complexes, where ppyH is 2-phenylpyridine and N^N is 2,2'-bipyridine (bpy), 6-phenyl-2,2'-bipyridine (pbpy), and 6,6'-diphenyl-2,2'-bipyridine (dpbpy) for complexes 1, 2, and 3, respectively, have been investigated in detail. The photoluminescence performance in solution decreases from 1 to 3 upon attachment of phenyl groups to the ancillary ligand. The absorption spectra recorded over time suggest that complex 3 is less stable compared to complexes 1 and 2 likely due to a nucleophilic-assisted ancillary ligand-exchange reaction. To clarify this behavior, the temperature dependence of the experimental intrinsic deactivation rate constant, k(in) = 1/τ, has been investigated from 77 K to room temperature. Temperature-dependent studies show that nonemitting metal-centered (MC) states are accessible at room temperature for complex 3. The experimental results are interpreted with the help of theoretical calculations performed within the density functional theory (DFT) approach. Calculations suggest that attachment of a phenyl group to the ancillary ligand (2) promotes the temperature-independent deactivation pathways, whereas attachment of a second phenyl group (3) also makes the temperature-dependent ones accessible through population of nonradiative (3)MC excited states.

Reactions of the [Fe(CN) 5 NO] 2À complex with biologically relevant thiols (H n RS ¼ cysteine, N-acetylcysteine, ethyl cysteinate and glutathione) are initiated by the nucleophilic attack of a thiolate (RS nÀ ) on the N atom of the NO + ligand in the complex to form [Fe(CN) 5 N(O)SR] (n+2)À . The N-S bond in the latter complex is, however, weak and can undergo both heterolytic and homolytic splitting. The former process makes the synthesis reaction reversible, whereas the latter is responsible for the spontaneous redox decomposition:The rate of the monomolecular reaction is controlled by an inductive effect in the thiol with an additional stabilisation coming from formation of a six-membered ring in the case of the N-acylated compounds. In the presence of thiolate excess, the RS (nÀ1)À radicals are transformed into the more stable RSSR (2nÀ1)À radicals, which are scavenged by both [Fe(CN) 5 N(O)SR] (n+2)À and [Fe(CN) 5 NO] 2À . The former reaction initiates, whereas the latter terminates, chain reactions of the catalysed redox decomposition. The catalytic decomposition (in the thiol excess) is much faster than the spontaneous decay (in the nitroprusside excess) but leads to the same final products. The Fe(I) reduction product is identified by UV/Vis, IR, electrochemical and EPR methods. The effect of molecular oxygen is investigated and explained. The mechanism is interpreted in terms of intermediate [Fe(CN) 5 N(O)(SR) 2 ] (2n+2)À complex formation via nucleophilic attack and its decay mainly via homolytic splitting of the N-S bond. To verify the mechanism, a simple reaction model is constructed, based on the assumption that the RSNO (nÀ1)À ligands are mostly responsible for the [Fe(CN) 5 N(O)(SR)] (n+2)À reactivity and their electronic properties are discussed within the DFT framework.

Chiral, facial tris-cyclometalated Ir(III) complexes, fac-Delta-Ir(pppy)(3), fac-Lambda-Ir(pppy)(3), fac-Lambda-IrL (where pppy is (8R,10R)-2-(2'-phenyl)-4,5-pinenopyridine and L is a tripodal ligand comprising three pppy moieties connected through a mesityl spacer) have been synthesized and characterized. In IrL, NMR and CD studies indicate that only one diastereomer is formed, with the Lambda configuration at the metal center, whereas enantiopure pppy yields the fac-Lambda- and the fac-Delta-stereoisomer in a ratio 2:3. fac-Lambda-IrL was structurally characterized using X-ray crystallography. The luminescence properties including CPL, of the three complexes and their sensitivity to dioxygen were examined.