Highly Symmetrical Tetranuclear Cluster Complexes Supported by p‐tert‐Butylsulfonylcalix[4]arene as a Cluster‐Forming Ligand

Square‐planar tetranuclear clusters [M4(L)(AcO)4(μ4‐OH)]– (M = MnII, CoII, and NiII) are synthesized using tetra‐anionic p‐tert‐butylsulfonylcalix[4]arene (L4–) as a cluster‐forming ligand. Three complexes are crystallographically isostructural, being crystallized in the triclinic crystal system with space group P1̄ . The calix[4]arene acts as a tetrakis fac‐tridentate ligand through four phenoxo and four sulfonyl oxygen atoms to form square arrangement of four metal ions, which are further bridged by four chelating acetate ions and one hydroxo ion in a μ4 manner to complete the hexacoordination of each metal center. Although the whole molecule of each complex is crystallographically independent, the molecule is highly symmetrical with a pseudo‐four‐fold axis lying on the μ4‐OH– group. The tetranuclear clusters are stable enough to maintain the core structures even in highly dilute solution (≈10 μM), which was confirmed by mass spectroscopic study, however, bridging acetates were easily exchanged by other carboxylate chelates to form derivatives such as [M4(L)(BzO)4(OH)]–. Metal–metal interactions were investigated by means of magnetic susceptibility, and it was revealed that both ferro‐ and antiferromagnetic interactions occur in the NiII complex depending on the bridging angles of Ni–O–Ni. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)