STABILITY-CONSTANTS OF THE ZINC(II), CADMIUM(II) AND MERCURY(II) COMPLEXES OF THE MONO-AZA CORONANDS 1,4,7,10-TETRAOXA-13-AZACYCLOPENTADECANE (L1), 1,4,7,10,13-PENTAOXA-16-AZACYCLOOCTADECANE (L2) AND 1,4,7-TRIOXA-10-AZACYCLODODECANE (L3) - CRYSTAL AND MOLECULAR-STRUCTURES OF THE CADMIUM COMPLEXES OF L1 AND L2

The stability constants for the 1:1 complexes of zinc, cadmium and mercury with 1,4,7,10-tetraoxa-13-azacyclopentadecane (L1), 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (L2) and 1,4,7-trioxa-10-azacyclododecane (L3) have been determined potentiometrically (0.1 M NEt4ClO4, 95% methanol). Reaction between L1 or L2 and cadmium nitrate tetrahydrate in methanol results in the isolation of colourless crystalline solids. Crystals of [Cd(L1)(NO3)2] are monoclinic, space group P2(1)/c with a = 7.614(2), b = 28.566(2), c = 7.707(l) angstrom, beta = 107.364(9)-degrees; R = 0.025, R(w) = 0.027 for 2195 (I > 3sigma(I)) reflections. The structure of [Cd(L1)(NO3)2] consists of an almost planar macrocyclic ligand enclosing a cadmium ion in its cavity, with a monodentate and a bidentate nitrate ligand coordinating the cadmium ion on opposite sides of the macrocycle. Crystals of [Cd(L2)(NO3)2] are orthorhombic, space group Pca2(1) with a = 8.738(11), b = 14.140(9), c = 15.176(8) angstrom; R = 0.019, R(w) = 0.022 for 3058 (I > 2.5sigma(I)) reflections. The structure of [Cd(L2)(NO3)2] consists of a cadmium atom enclosed in the cavity of the macrocycle, with a monodentate and a bidentate nitrate ligand on opposite sides of the macrocycle. Two of the oxygen atoms of L2 in [Cd(L2)(NO3)2] do not coordinate the cadmium ion, but the remaining donor atoms of the macrocycle form an almost planar assembly around the cadmium.