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Co-ordination tendency of [3k]aneN k polyazacycloalkanes. Thermodynamic study of solution equilibria

1991; Royal Society of Chemistry; Issue: 5 Linguagem: Inglês

10.1039/dt9910001171

2050-5671

Andrea Bencini, Antonio Bianchi, Mauro Micheloni, Piero Paoletti, Enrique García‐España, Miguel Ángel Niño,

Molecular Sensors and Ion Detection

Equilibria between polyazacycloalkanes of the series [3k]aneNk(k= 3–11) and the bivalent metal ions of Mn through Zn have been studied. The stability constants (log K) for the complexes of Mn2+, Cu2+ and Fe2+ with 1,4,7,10,13,16-hexaazacyclooctadecane (L4), 1,4,7,10,13,16,19-heptaazacyclo-henicosane (L5) and 1,4,7,10,13,16,19,22-octaazacyclotetracosane (L6) have been determined potentiometrically in 0.15 mol dm–3 NaClO4 at 25°C: [MnL4]2+, 10.50; [MnL6]2+, 6.27; [CuL4]2+, 24.40; [CuL5]2+, 19.48; [Cu2L5]4+, 30.49; [Cu2L6]4+, 35.25; and [FeL5]2+ 12.09. The enthalpy changes (–ΔH°/kcal mol–1) for the formation of [CuL4]2+(23.9), [CuL5]2+(19.7) and [NiL5]2+(11.7) have been measured by means of microcalorimetric techniques. The results are discussed in terms of the increasing number of donor atoms and size of the macrocycles. As the size increases the co-ordination features of the metal compleses largely depend on the metal ion.