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.

Reaction of Cd(ClO4)2 with the potentially tetra-, penta- and hexadentate 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. Each of these complexes have been characterised by crystallography. Further more 1H NMR shows that these structures are retained in solution.