p-tert-Butylthiacalix[6]arene as a Clustering Ligand. Syntheses and Structures of Co^II₅, Ni^II₄, and Mixed-Metal M^IINi^II₄ (M = Mn, Co, and Cu) Cluster Complexes, and a Novel Metal-Induced Cluster Core Rearrangement

Using p-tert-butylthiacalix[6]arene (H₆L) as a clustering ligand, five cluster complexes having Co^II₅ (2), Ni ^II₄ (3) and M^IINi^II₄ (M = Co^II (4), Mn^II (5), and Cu^II (6)) cores were synthesized. In all the complexes except for 3, a pinched conic L^6- acts as a pentanucleating ligand that involves a similar pyramidally arranged cluster core. Each mixed metal complex 4-6 involves four tetragonally arranged Ni^II ions occupying the basal plane of the pyramid and a M ^II ion placed at the apex position. In 3, H₂L ^4- is in a cone conformation and the four Ni^II ions are arranged on the donor surface of H₂L^4- in a zigzag manner. The mixed metal complexes 4-6 are synthesized by reacting 3 and the appropriate M(AcO)₂ in a 1:1 ratio with a novel metal-induced core rearrangement occurring. In this reaction, the insertion of a M^II ion at the apex position forces the calixarene to take a cone conformation and the Ni^II₄ array rearranges to form a tetragonal cluster.