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-azacyclo- pentadecane (L), 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (L) and 1,4,7-trioxa-10-azacyclododecane (L) have been determined potentiometrically (0.1 M NEtClO, 95% methanol). Reaction between L or L and cadmium nitrate tetrahydrate in methanol results in the isolation of colourless crystalline solids. Crystals of [Cd(L)(NO)] are monoclinic, space group P2/c with a=7.614(2), b=28.566(2), c=7.707(1) Å, β=107.364(9); R=0.025, R=0.027 for 2195 (I> 3σ(I)) reflections. The structure of [Cd(L)(NO)] 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(L)(NO)] are orthorhombic, space group Pca2 with a=8.738(11), b=14.140(9), c=15.176(8) Å; R=0.019, R=0.022 for 3058 (I> 2.5σ(I)) reflections. The structure of [Cd(L)(NO)] 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 L in [Cd(L)(NO)] do not coordinate the cadmium ion, but the remaining donor atoms of the macrocycle form an almost planar assembly around the cadmium