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 Co-5(II) (2), Ni-4(II) (3) and (MNi4II)-Ni-II (M = COII (4), Mn-II (5), and Cu-II (6) cores were synthesized. In all the complexes except for 3, a pinched conic L6- 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, H2L4- is in a cone conformation and the four Ni-II ions are arranged on the donor surface of H2L4- 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-4(II) array rearranges to form a tetragonal cluster.