Transition metal and lanthanide cluster complexes constructed with thiacalix[n]arene and its derivatives

This review deals with the formations, structures, and properties of transition metal and lanthanide clusters supported by thiacalix[n]arene and its oxidized derivatives, sulfinylcalix[4]arene and sulfonylcalix[4]arene. Each thiacalix[n]arene possesses donor atoms both on the lower rim position (phenol oxygen atoms) and on the cyclic framework itself (-S-, -SO-, or -SO₂-), and behaves as a multidentate multi-nucleating ligand to support the formation of a phenoxo-bridged cluster core. For first row transition metals, calix[4]arenes offer a platform for assembling the metal ions via four fac-tridentate coordination sites, and planar tri- and tetra-nuclear clusters are formed. A larger and more flexible thiacalix[6]arene could bind up to five metal ions inside the coordination cavity formed when it adopts the pinched cone conformation. Sulfonylcalix[4]arene shows a strong affinity to lanthanide ions through phenoxo and sulfonyl oxygen donors, and yields a variety of cluster compounds involving di-, tetra-, octa-, and dodeca-nuclear cores, achieved by controlled synthetic conditions.