Synthesis, structure and property of three divalent metal complexes of the piperidinoacetyl-containing calix[4]arene

Three new mononuclear complexes [Cd(L)](ClO₄)₂·4(MeCN) (1) (L?=?5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis(piperidinocarbonylmethoxy)calix[4]arene), [Zn(L)](ClO₄)₂·4(MeCN)·CH₂Cl₂ (2), [Cu(L)](ClO₄)₂·3(MeCN)·Et₂O (3) have been synthesized and characterized by elemental analysis and X-ray single crystal diffraction (CCDC: 838342, 838343 and 838344). The results of the crystal structural analyses show that calix[4]arene backbones in 1, 2, 3 are fixed in the cone conformation while the divalent metal cations (Cd, Zn and Cu) are coordinated with the discrepant geometry. The cadmium ion in 1 is eight-coordinated with four carbonyl oxygen atoms and four ethereal oxygen atoms in the low rim of calix[4]arene, whereas zinc ion in 2 and copper ion in 1 are four-coordinated with the acyl oxygen atoms. The atomic net charges distribution and frontier molecular orbital energies were obtained by Gaussian 98 program with DFT method at B3LYP/lanl2dz level. Furthermore, the SOD-like activities of 3 were measured by xanthine/xanthine oxidase-NBT assay at pH 7.2 and 7.8.