REINFORCED PIPERAZINE RINGS CONTAINING POLYAMINES - METAL-COMPLEX EQUILIBRIA AND STRUCTURAL STUDIES

The three reinforced polyamines bis(2-piperazinylethyl)amine (L1), bis (2-piperazinylethyl) methylamine (L2) and bis(2-methylpiperazinylethyl )methylamine (L3) have been prepared. The basicity behaviour in aqueou s solution has been studied by potentiometry (25 degrees C, I = 0.15 m ol dm(-3), NaCl) and H-1, C-13 NMR spectroscopy, yielding: log K-1 = 9 .52(1), 9.12(1), 8.16(1); log K-2 = 8.78(1), 8.65(1), 7.75(1); log K-3 = 8.06(1), 7.38(1), 6.97(1) for L1, L2 and L3 respectively. Only for L1, we found log K-4 = 2.14(1). The stability constants for Cu(II) and Cd(II) complexes have been determined by potentiometry. The crystal s tructure of the pentaprotonated species [H(5)L1]Cl-5 . 3H(2)O is repor ted. Crystals are monoclinic, space group P2(1)/a, with a = 12.179(6), b = 11.864(3), c = 16.853(5) Angstrom, beta = 100.56(3)degrees, Z = 4 , R = 0.065. (C) 1998 Elsevier Science S.A.