NEW POLYNUCLEAR LUMINESCENT TRICARBONYL RE(I) COMPLEXES CONTAINING MULTI-NITROGEN HETEROCYCLIC LIGANDS

Three different classes of rhenium(I) compounds have been studied in this thesis. New luminescent complexes of general formula [Re2(μ-X)2(CO)6(μ-pydz)] have been synthesized, in which the bridging ancillary ligands are OR- or SR- anions. Intriguing electro-chemical properties have been evidenced, differentiating the OR derivatives from the SR one and the previously reported halide analogues. The bis(benzenethiolato) derivative exhibits a very small electrochemical energy gap and absence of photoluminescence. The best emitting properties, closely comparable to those of the dichloro complex, are shown by the bis(pentafluorophenolato) derivative (Φ = 5.5% in deaerated toluene). A second class involves new neutral dinuclear complexes of rhenium containing bridging 1,2,4-triazole ligands (4-(p-tolyl)-4H-1,2,4-triazole, 4-(n-propyl)-4H-1,2,4-triazole, 4-(4’-nitrophenyl)-4H-1,2,4-triazole). The complexes were designed to obtain a blue shift of the emission compared to the corresponding diazine complexes. The absorption spectra and the electrochemical data show that the rising of the HOMO-LUMO gap has actually occurred, but the intensity of the emission is too weak to have any applicative interest. Experiments trying to obtain complexes in which triazolate ligands coexist with a diazine chromophore are also described. The possible synthesis of analogous derivatives containing 5-aryl tetrazoles (is also under investigation. In both the triazole and tetrazole cases, the new species are examples of a very limited family of molecular complexes in which such ligands are bound to metals in low oxidation state. Finally, the reactions of the unsaturated tetranuclear cluster [Re4(μ3-H)4(CO)12] with diazines bearing substituents in 4 and 5 positions (4,5-bis(trimethylsilyl)pyridazine, 6,7-dihydro-5H-cyclopentapyridazine) and with 1,8-naphthyridine have been performed. The reaction pathways and the influence of the substituents on the fragmentation reactions have been investigated. The photophysical properties of the main reaction products have been preliminary determined.