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 26,27,28-tetrakis(diethylcarbamoylmethox y)calix[4] arene (L) in the cone conformation have been synthesised fo r the first time. Single-crystal structure determinations have been ca rried 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 o xygen atoms of L. The copper complex is somewhat different with the fo ur 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 acc ommodate the metal cation in a distorted-octahedral environment. Molec ular-mechanics calculations have been carried out to investigate the r emarkable versatility of L as a metal cation receptor.