Interaction of lead(II) with highly-dentate linear and cyclic polyamines

Abstract

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), 1,4,7,10,13,16,19,22,25,28,31-undecaazacyclotritriacontane (L6) and 1,4,7,10,13,16,19,22,25,28,31,34-dodecaazacyclohexatriacontane (L7) belonging to the [3k]aneNg series and with their related open-chain, terminally methylated polyamines 1,14-bis(methylamino)-3,6,9,12-tetraazatetra-decane (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 0.15 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 P21/n, Z= 2, a= 9.052(9), b= 11.400(9), c= 18.689(8)A, β= 94.42(6)°, 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 A). A fifth nitrogen and three oxygens of two perchlorate anions are weakly interacting at much larger distances (Pb–N 3.04; Pb–O 2.98, 3.38, 3.41 A). 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.