Showing papers by "Vieri Fusi published in 1992"

Synthesis and protonation behaviour of the macrocyclic ligand 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane and of its bicyclic derivative 4,7,10,17,23-pentamethyl-1,4,7,10,13,17,23-heptaazabicyclo[11.7.5]-pentacosane. A potentiometric and 1H and 13C NMR study

Abstract: The synthesis and characterization of the new macrocyclic ligand 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane (L) and of its bicyclic derivative 4,7,10,17,23-pentamethyl-1,4,7,10,13,17,23-heptaazabicyclo[11.7.5]pentacosane (L1) is reported. The basicity behaviour of both polyamines has been studied by potentiometry in 0.15 mol dm–3 NaClO4 solution at 298.15 K and the relevant protonation constants have been determined. 1H and 13C NMR spectroscopy of L and L1, at various pH values, allows the main features of the protonation patterns to be determined.

Synthesis, crystal structure and ligational properties of a new macrotricyclic ligand

Abstract: The synthesis and characterization of the new macrotricycle 10,22,28,32-tetraoxa-1,4,7,13,16,18-hexaazatricyclo[17.5.5.57,13]tetratriacontane L is reported. Its basicity in aqueous solution has been investigated by potentiometric and spectroscopic (1H, 13C NMR) techniques. The basicity constants have been determined (25 °C, I= 0.15 mol dm–3) in two ionic media. Macrotricycle L behaves as a hexaprotic base: log K1= 10.27(3), log K2= 9.52(3), log K3= 7.12(3), log K4= 4.62(3), log K5= 2.80(3), log K6= 2.27(3) in NaClO4 and log K1= 10.09(3), log K2= 9.27(3), log K3= 6.54(3), log K4= 4.88(3), log K5= 3.75(3), log K6= 3.07(3) in NaCl. The constants relative to the equilibrium Cl–+ HnLn+⇌ HnLCl(n–1)+ have been measured: n= 5, log K= 2.48(3); n= 6, log K= 3.59(3). The crystal structure of L has been determined by single-crystal X-ray analysis. The compound crystallizes in a triclinic unit cell (space group P, Z= 2) with lattice constants a= 8.984(5), b= 12.122(2), c= 14.667(3)A, α= 109.52(2), β= 105.47(3), γ= 95.24(3)°. Least-squares refinement converged at R= 0.088 (R′= 0.075) for 3198 unique reflections with I > 4σ(I). The structure shows that the molecule has a skewed cylindrical shape, the bases being formed by the two N2O2 macrocycles with the N(CH2CH2)2 chains constituting the walls. The cylindrane L binds two Li+ ions and the resulting complex has been studied by 7Li NMR spectroscopy. Copper(II) and cadmium(II) complexes with L have been investigated in aqueous solution and their stability constants determined by potentiometric techniques. For both metals the following species have been found: [ML]2+, [MLH]3+, [ML(OH)]+ and [ML(OH)2].