6533b85ffe1ef96bd12c2544

RESEARCH PRODUCT

Thermodynamic study of the interaction of long open-chain polyazaalkanes with cobalt(II) and nickel(II) ions

subject

description

Complexation equilibria between the open-chain terminally methylated polyamines 1,14-bis(methylamino)-3,6,9,12- tetraazatetradecane (L1), 1,17-bis(methylamino)-3,6,9,12,15-pentaazaheptadecane (L2), 1,20-bis(methylamino)- 3,6,9,12,15,18-hexaazaicosane (L3) and 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (L4) with Co2+ and Ni2+ have been studied by means of potentiometric and spectrophotometric methods in 0.15 mol dm−3 NaClO4 aqueous solution at 298.15 K The stability constants for the complexes formed have been determined from e.m.f, data. All these ligands form mononuclear ML2+ complexes of similar stability with Co2+ and Ni2+. Binuclear Co2L44+, Ni2L34+ and Ni2L44+ are also formed. The equilibrium constants of the complexes of L1–L4, which are the open-chain counterparts of the macrocyclic ligands [3k]aneNk (k=6−9), reveal that only [18]aneN6 with Co2+ and Ni2+, and [21]aneN7 with Co2+. present enhanced stability (macrocyclic effect) with respect to L1–L4. However this effect has not been observed for binuclear complexes.