Molybdotellurates containing the 1-methyl-, 2-methyl- and 4-methyl imidazolium cations

Four molybdotellurates containing the 1-methylimidazolium, 2-methylimidazolium and 4-methylimidazolium cations have been synthesized and their structures: [2-H2-methyl-imz]6[TeMo6O24 ]·2H2O (2), [2-H2-methyl-imz]6[TeMo6O24 ]·2(2-H-methyl-imz)·2H2O (3) and [4-H2-methyl-imz]6[TeMo6O24 ]·Te(OH)6 (4) determined by X-ray diffraction methods. The protonated organic bases are bonded to the anion in the crystal by hydrogen bonds, except for (4) where the crystal structure consists of discrete [TeMo6O24]6– anions and Te(OH)6 units, both bonded to 4-methylimidazolium cations by hydrogen bonds. The hydrogen bonds were studied as a function of the unit charge of the oxygen atoms of the [TeMo6O24]6– anion. Distortions of the central octahedron of polyanions of formula [XMo6O24]n– (X=AlIII, MoVI, TeVI and IVII), and polyanions of formula [H6YMo6O24]n–, (Y=CoII, CuII, ZnII, CrIII, RhIII and PtIV) are discussed. 95Mo n.m.r spectroscopy of compounds [1-H2-methyl-imz]6[Te-Mo6O24]·Te(OH)6 (1), (2) and (4) indicates the existence of an octahedral oxygen atom arrangement around the molybdenum and a pH variation experiment, carried out with compound (1), confirmed the existence of hydrolytic processes of the compounds in aqueous solution. 125Te n.m.r. studies permitted identification of the Te atom in the [TeMo6O24]6– kernel in all compounds; the presence of two different Te(OH)6 moieties in compounds (1) and (4) was also detected. The similarity between the spectra of both compounds could indicate that (1) has the same structural arrangement as (4). Finally, the thermal behaviour and the thermal stabilities of the complexes as a function of the organic cation were studied.     

PHOTOELECTRIC EFFECTS FROM CHLOROPHYLL a IN BILAYER MEMBRANES

Abstract— The photophysical and photochemical properties of thiophene derivatives have been studied by fluorescence and by 353 nm laser flash spectroscopy. α-Terthienyl and its derivatives show a moderate fluorescence quantum yield (less than 0.1) in cyclohexane, ethanol, or TritonX–100 micelles. An additional thiophene ring increases this value to 0.2 in ethanol or micelles. The transient triplet state of the six thiophenes is characterized by strong absorptions (ε⋍ 50000 M ^-1 cm^-1) in the visible region. These triplet states are very long lived. They react with oxygen, producing singlet oxygen very efficiently because of their high quantum yield of triplet formation (0.1 to 0.3). They do not react with excellent hydrogen or electron donors such as indole, N-acetyl tryptophanamide or cysteine. The hydrophobic thiophenes investigated are, therefore, Type II photodynamic agents almost exclusively.