Novel multidentate pyridyl/thiazolyl ligands containing terpyridine units: formation of dinuclear and trinuclear double helicate complexes

Three new multidentate N-donor ligands L1-L3, which contain a combination of pyridyl and thiazolyl donor units, have been prepared starting from 2,2':6',2''-terpyridine. The extended linear sequence of ortho-linked N-donor heterocycles (five for L1; six for L2; and seven for L3) is reminiscent of the well-known oligopyridines, although they have different coordination properties due to the presence of five-membered thiazolyl rings which result in natural breaks of the ligand backbone into distinct bidentate or terdentate domains. Thus, the pentadentate ligand L1 partitions into terdentate and bidentate domains to give a dinuclear double helicate [M2(L1)2]4+ with Cu(II). The hexadentate ligand L2 partitions into two terdentate domains to give dinuclear double helicates [M2(L2)2]4+ with six-coordinate first-row transition metals dications (M=Ni and Co). The heptadentate ligand L3 partitions into two terminal bidentate and a central terdentate domains to give a trinuclear double helicate [Cd3(L3)2]6+ with Cd(II). The formation of these complexes highlights the fact that the thiazole group is instrumental in instructing the partitioning of the ligand, which in turn controls the formation of the helicate complexes.