NMR investigation of the structure and stability of complexes of dibenzomethylphosphonyl-20-crown-7 with the ions of the alkali and alkaline-earth metals

Abstract

The complex-forming properties of macrocyclic polyethers containing additional functional groups (C=O, OH, P=O, etc.) have been investigated by various workers [1-3]. It has been established that the introduction of additional functional groups in some cases leads to a lowering of the selectivity of the crown ethers, which is frequently connected with dominating role of these functional groups in the binding of metal ions as compared with the ether oxygen atoms [2, 4]. A study made by us previously [3] of complex formation by a phosphonylcontaining macrocyclic polyether dibenzomethylphosphonyl-20-crown-7 (MPC) (see formula in Fig. i) with the picrates of the alkali and alkaline-earth metals in a medium with a low dielectric constant (a mixture of dichloroethane and tetrahydrofuran) show that under these conditions complexes of the type ~of separated ion pairs are formed. The stability of the complexes of I~C with the picrates of alkali and alkaline-earth metals changes in the sequence