p-tert-Butylthiacalix[6]arene as a Clustering Ligand. Syntheses and Structures of CoII5, NiII4, and Mixed-Metal MIINiII4 (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 CoII5 (2), NiII4 (3) and MIINiII4 (M = CoII (4), MnII (5), and CuII (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 NiII ions occupying the basal plane of the pyramid and a MII ion placed at the apex position. In 3, H2L^4- is in a cone conformation and the four NiII 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 MII ion at the apex position forces the calixarene to take a cone conformation and the NiII4 array rearranges to form a tetragonal cluster.