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

Abstract

Reaction of Cd(ClO 4) 2 with the potentially tetra- (L 1), penta- (L 2) and hexadentate (L 3) pyridine–thiazole-containing ligands gives [Cd 2(L 1) 3(H 2O)][ClO 4] 4 (a dinuclear triple helicate), mononuclear [Cd(L 2)(ClO 4) 2], and [Cd 2(L 3) 2(ClO 4)(CH 3CN)][ClO 4] 3 (a dinuclear double helicate), respectively. In [Cd 2(L 1) 3(H 2O)][ClO 4] 4 two of the ligands L 1 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(L 2)(ClO 4) 2], L 2 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 H 6 protons, which are directed towards each other. In [Cd 2(L 3) 2(ClO 4)(CH 3CN)][ClO 4] 3, the potentially hexadentate ligand L 3 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.