ON THE SOLID-STATE CONFORMATIONS OF 18-CROWN-6 COMPLEXES

A procedure for displaying macrocylic torsion angles as a map on polar coordinates is discussed with reference to the solid-state conformati ons of 18-crown-6 and its complexes. The maps aid in comparisons of re lated structures, in the perception of pseudo-symmetry elements, and i n the classification of the conformations of 18-crown-6. Only four con formational groups are found in the 1:1 complexes of 18-crown-6 with s odium, potassium, rubidium, cesium, thallium(I), calcium and strontium cations. The relationship of donor number, mean cavity radius and eff ective ionic radius combined with skeletal drawings of the donors and the polar map of the torsion angles provide a composite picture of the structures and insight into the balance between cation-donor interact ion energy and conformational energy.