Showing papers by "Rosario Scopelliti published in 1999"
TL;DR: The acid-catalyzed condensation of pyrrole with p- or m-hydroxyacetophenone led to the formation of meso-tetramethyltetrakis(hydroxyphenyl)calix[4]pyrroles occurring in three isomeric forms, with the cone conformer displaying topologically variable multi-site or multi-point surfaces for binding neutral or anionic substrates as discussed by the authors.
65 citations
TL;DR: In this paper, a photophysical study of both the ligand and metal-centred luminescence of lower-rim substituted calix[4]arene (L) was performed.
Abstract: The lower-rim substituted calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy)calix[4]arene (L) has been synthesized and characterised by the single-crystal structure of its acetonitrile adduct, L·2MeCN (monoclinic, space group P21/c). The ligand adopts a cone conformation and a Δ enantiomeric form with the four phosphinoyl arms in a δδδδ configuration. The cone conformation is maintained in organic solution where L displays a time-averaged C4 symmetry. Trivalent lanthanum ions interact with L in acetonitrile to yield both 1∶1 (log β1 = 11.4 ± 1.5) and 1∶2 (log β2 = 19.6 ± 1.8) complexes; two forms of the 1∶1 complex are identified depending on the water content of the solutions. A photophysical study of both the ligand- and metal-centred luminescence of complexes of La, Eu and Tb points to L having a moderate quantum yield (ca. 10%, ligand-centred luminescence) and being a poor sensitiser of europium and terbium ions. It confirms the presence of differently solvated 1∶1 (and 1∶2) complexes, depending on the solvent composition. The lifetimes of the metal-centred luminescence of the unhydrated 1∶1 and 1∶2 complexes are long, in the range 1.4–2.4 ms for Eu and 1.7–7.3 ms for Tb, which indicates that the lanthanide(III) ions are well encapsulated in the cavity formed by the donor groups of the calix[4]arene molecule(s).
39 citations
TL;DR: In this article, the reaction of meso-octaethylporphyrinogen-lanthanide complexes with NaC10H8 in an ethylene or acetylene atmosphere leads to the isolation of dimeric species.
33 citations
TL;DR: In this paper, the crystal and molecular structure of 1,4,7,10-tetrakis(N-benzylcarbamoylmethyl)-1,4-7, 10tetraazacyclododecane, L1, revealed an S2-symmetric molecule.
Abstract: The crystal and molecular structure of 1,4,7,10-tetrakis(N-benzylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane, L1, revealed an S2-symmetric molecule. One pair of pendant arms is involved in intramolecular hydrogen bonding while the other interacts with two other ligand molecules through strong intermolecular hydrogen bonds. In solution, the ligand adopts a similar geometrical arrangement at low temperature but complexes with EuIII and LuIII display an averaged C4-symmetry on the NMR timescale. One isomer only was detected, as reported for similar complexes, and the arrangement around EuIII and LuIII appears to be rigid while it is more fluxional around LaIII. Rotation of the benzyl group around the amide function was observed for EuIII and a dynamic NMR study in the range 253–333 K yielded ΔH
‡ = 43.0 ± 0.1 kJ mol–1, ΔS
‡ = –49.3 ± 0.4 J K–1 mol–1 and k298 = 47.7 ± 1.1 s–1. In the solid state, anhydrous eight-co-ordinate complexes were isolated and high resolution luminescence spectroscopy of EuIII in the europium and Eu-doped compounds of La, Gd and Lu confirmed a site symmetry close to C4 along the lanthanide-series. Energy transfer from the L13ππ* state to the Tb(5D4) excited state is sizable leading to an absolute quantum yield of 6.4% in MeCN, while the EuIII luminescence is only poorly sensitized, possibly because of photoinduced electron transfer processes. The Tb(5D4) and Eu(5D0) lifetimes for both solid state samples and solutions in MeCN are consistent with no water molecule in the inner co-ordination sphere but addition of water results in the ninth co-ordination site being bound to H2O: number of bound waters, q = 0.96 (Eu) and 0.71 (Tb) in MeCN + 2 M H2O and 1.19 (Eu) and 1.30 (Tb) in water. The relaxivity r1 of the gadolinium(III) complex is pH dependent and varies between 4.08 (pH 0.8), 1.88 (6.7) and 6.14 (11.1) mM–1 s–1.
26 citations
TL;DR: Nickel(II)-meso-octaethylporphyrinogen dianion behaves as a π-extended ligand binding four M(CO)3 [M = Cr, Mo] fragments at the periphery, so that the porphrinogen can assemble five metal centers around itself as discussed by the authors.
16 citations
Journal Article•
12 citations
TL;DR: The electrophilic reactivity of the porphodimethene skeleton towards nucleophiles led the establishment of a synthetic methodology to unprecedented forms of porphyrinogen containing the vinylidene substituents as well as other functionalities in the meso-positions as mentioned in this paper.
11 citations
TL;DR: In this article, the title compound, C 24 H 21 N 3 O 4, consists of a benzodiazepine moiety and an oxadiazole ring fused together, with the seven-membered ring in a 'boat' conformation.
Abstract: This paper represents one of the few structural reports on 2,3-benzodiazepines. The title compound, C 24 H 21 N 3 O 4 , consists of a benzodiazepine moiety and an oxadiazole ring fused together, with the seven-membered ring in a 'boat' conformation. The molecules are linked into pairs by N-H…O hydrogen bonds. The title compound is an interesting antagonist at non-NMDA (N-methyl-D-aspartate) receptors.
2 citations