Versatile cation complexation by a calix[4]arene tetraamide (L). Synthesis and crystal structure of [ML][ClO4]2·nMeCN (M = FeII, NiII, CuII, ZnII or PbII)

Abstract

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. Molecularmechanics calculations have been carried out to investigate the remarkable versatility of L as a metal cation receptor.