VERSATILE CATION COMPLEXATION BY A CALIX[4]ARENE TETRAAMIDE(L) - SYNTHESIS AND CRYSTAL-STRUCTURE OF [ML][CLO4](2)CENTER-DOT-NMECN (M=FE-II, NI-II, CU-II, ZN-II OR PB-II)

Transition-metal complexes of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(diethylcarbamoylmethoxy)calix[4] arene (L) in the cone conformation have been synthesised for the first time. Single-crystal structure determinations have been carried out on the complexes of Fe2+, Ni2+, Cu2+ and Zn2+, as well as of Pb2+, the stoichiometry in each case being assigned as [ML][ClO4](2).nMeCN (n = 4-6). The structures of the complexes of Fe2+, Zn2+ and Pb2+ are broadly similar with the metal atoms co-ordinated to all eight oxygen atoms of L. The copper complex is somewhat different with the four Cu-O (amide) distances being very much shorter than the four Cu-O (ether) distances. A completely different structure is observed in the nickel complex, where L has undergone significant rearrangement to accommodate the metal cation in a distorted-octahedral environment. Molecular-mechanics calculations have been carried out to investigate the remarkable versatility of L as a metal cation receptor.