Abstract
The coordination features of the ligand 1,4,7,16,19,22-hexaza-10,13,25,28-tetraoxacyclotriacontane ( L1) towards Co(II), Ni(II), Cd(II) and Pb(II) have been studied in aqueous solution by means of potentiometric measurements (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 [M L1] 2+ complexes, the metal ion is coordinated by one of the two triamine moieties, while the other one does not participate in the coordination. In the binuclear complexes each metal ion is coordinated by one polyamine moiety. Such metal complexes can behave as receptors for anionic species as shown by the crystal structure of [Cd 2Ll(μ-NCS) 2Br 2] (space group P2 1 c , a = 12.900(4), b = 11.998(9), c = 13.10(2) A ̊ , β = 117.41(4)°, V = 1800(3) Å 3, Z = 2, R=0.0825, w R 2 = 0.2880). In this compound the two thiocyanate ions bridge the metal centers. The metal is coordinated to three adjacent nitrogens of the ligand and completes its coordination sphere by binding to a sulfur and a nitrogen of two different thiocyanates and a bromide ion.
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