BINUCLEAR METAL ASSEMBLIES INSIDE AN OXA-AZA MACROCYCLIC RECEPTOR

The coordination features of the ligand ,19,22-hexaza-10,13,25,28-tetr aoxacyclotriacontane (L1) towards Co(II), NL(II), Cd(II) and Pb(II) ha ve been studied in aqueous solution by means of potentiometric measure ments (298.1 K, I = 0.15 mol dm(-3)). The species present in solution and their stability constants have been determined. L1 forms mono- and dinuclear complexes in aqueous solution. In the [ML1](2+) complexes, the metal ion is coordinated by one of the two triamine moieties, whil e the other one does not participate in the coordination. In the binuc lear complexes each metal ion is coordinated by one polyamine moiety. Such metal complexes can behave as receptors for anionic species as sh own by the crystal structure of [Cd(2)L1(mu-NCS)(2)Br-2] (space group P2(1)/c, a = 12.900(4), b = 11.998(9), c = 13.10(2) Angstrom, beta = 1 17.41(4)degrees, V = 1800(3) Angstrom(3), Z = 2, R = 0.0825, wR(2) = 0 .2880). In this compound the two thiocyanate ions bridge the metal cen ters. The metal is coordinated to three adjacent nitrogens of the liga nd and completes its coordination sphere by binding to a sulfur and a nitrogen of two different thiocyanates and a bromide ion.