Cadmium-containing pyridyl–thiazole complexes: crystal structures and solution behaviour of mononuclear, dinuclear double helicate and dinuclear triple helicate complexes

Reaction of Cd(ClO4)2 with the potentially tetra- (L1), penta- (L2) and hexadentate (L3) pyridine–thiazole-containing ligands gives [Cd2(L1)3(H2O)][ClO4]4 (a dinuclear triple helicate), mononuclear [Cd(L2)(ClO4)2], and [Cd2(L3)2(ClO4)(CH3CN)][ClO4]3 (a dinuclear double helicate), respectively. In [Cd2(L1)3(H2O)][ClO4]4 two of the ligands L1 partition into two bidentate pyridyl–thiazole domains whereas the remaining ligand partitions into a bidentate (pyridyl–thiazole) and monodentate (coordinating pyridyl unit with a pendant thiazole) unit; one Cd(II) centre is coordinated by three bidentate ligand fragments, whereas the other is coordinated by two bidentate and one monodentate ligand fragments as well as a water molecule. This low-symmetry arrangement is retained in solution. In [Cd(L2)(ClO4)2], L2 acts as a planar pentadentate equatorial ligand with perchlorate anions coordinated at the axial sites; the ligand has a shallow helical twist to minimise steric interactions between the terminal pyridyl H6 protons, which are directed towards each other. In [Cd2(L3)2(ClO4)(CH3CN)][ClO4]3, the potentially hexadentate ligand L3 is partitioned into terdentate (pyridyl–thiazole–pyridyl) and bidentate (pyridyl–thiazole) coordination domains with a non-coordinated terminal pyridyl unit; each Cd(II) centre is coordinated by one terdentate and one bidentate ligand fragment, with the sixth site being occupied by MeCN at one Cd(II) site and a perchlorate anion at the other. Again, the low symmetry coordination mode of the ligands is retained in solution although the two metal centres become equivalent.