INTERACTION OF LEAD(II) WITH HIGHLY-DENTATE LINEAR AND CYCLIC POLYAMINES

The interaction of Pb2+ with the macrocyclic amines 1,4,7,10,13,16-hexaazacyclooctadecane (L1), 1,4,7,10,13,16,19-heptaazacyclohenicosane (L2), 1,4,7,10,13,16,19,22-octaazacyclotetracosane (L3), 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane (L4), 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane (L5), 1,4,7,10,13,16,1 9,22.25,28,31 -undecaazacyclotritriacontane (L6) and 1,4,7,10,13,16,19, 22,25,28,31,34-dodecaazacyclohexatriacontane (L7) belonging to the [3k]aneN(k) series and with their related open-chain, terminally methylated polyamines 1,14-bis(methylamino)-3,6,9,12-tetraazatetradecane (L8), 1,17-bis(methylamino)-3,6,9,12,15-pentaazaheptadecane (L9), 1,20-bis(methylamino)-3,6,9,12,15,18-hexaazaicosane (L10) and 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (L11) has been studied by potentiometry at 298.1 K in 0.1 5 mol dm-3 NaClO4. The cyclic amines L1 and L2 form only mononuclear complexes, while L3-L5 can form both mono- and bi-nuclear species. The largest amines of this series L6 and L7 form bi- and tri-nuclear lead(II) complexes. Of the open-chain ligands, L8 forms only mononuclear complexes, while L9-L11 form both mono- and bi-nuclear species. The crystal structure of the solid compound [Pb2L5][ClO4]4 has been solved by X-ray diffraction analysis [space group P2(1)/n, Z = 2, a = 9.052(9), b = 11.400(9), c = 18.689(8) angstrom, beta = 94.42(6)-degrees, R = 0.082 and R' = 0.068). It shows that both Pb2+ ions are tightly co-ordinated to four nitrogens of the macrocycle (Pb-N ranging from 2.27 to 2.71 angstrom). A fifth nitrogen and three oxygens of two perchlorate anions are weakly interacting at much larger distances (Pb-N 3.04; Pb-0 2.98, 3.38, 3.41 angstrom). The complex cation is situated around a crystallographic symmetry centre. The arrangement of the eight atoms around the lead ion is rather asymmetric leaving a zone free from co-ordinated donor atoms which is believed to be occupied by a lone pair of electrons.