INTERACTION OF LONG OPEN-CHAIN POLYAZAALKANES WITH HYDROGEN AND COPPER(II) IONS

The series of polyazaalkanes 1,16-dimethyl-1,4,7,10,13,16-hexaazahexadecane (Me2pentaen), 1,19-dimethyl-1,4,7,10,13,16,19-heptaazanonadecane (Me2hexaen), 1,22-dimethyl-1,4,7,10,13,16,19,22-octaazadocosane (Me2heptaen), 1,25-dimethyl-1,4,7,10,13,16,19,22,25-nonaazapentacosane (Me2octaen), and 1,28-dimethyl-1,4,7,10,13,16,19,22,25,28-decaazaoctacosane (Me2nonaen) have been synthesized and characterized. Their protonation behavior has been studied potentiometrically at 298.15 K in 0.15 mol dm-3 NaClO4 as well as by C-13 NMR spectroscopy. A protonation pattern that minimizes electrostatic repulsions between polyammonium sites has been found. The interaction of these polyamines with copper(II) has been studied by potentiometric measurements under the same experimental conditions. All these ligands form both mono- and binuclear copper(II) complexes. While the stability of the mononuclear complexes remains almost unaffected along the series, that of the binuclear complexes increases from log K = 28.031 (7) for [Cu2(Me2pentaen)]4+ to log K = 41.17 (3) for [Cu2(Me2nonaen)4+. The formation enthalpies of the [CuL]2+ species determined by direct microcalorimetry present an almost constant value of about -25.0 kcal mol-1 for all the terms of the series.