Molecular design using electrostatic interactions. Part 2: Synthesis and properties of flexible dipodand di- and tetra-cations with restricted conformations. Charge, shape and size in molecular complexation

A number of dipodand dications and tetracations were synthesised with struc tures based on 1,2,4,5-, penta- and hexa-substituted benzene, DABCO substit uents providing the positive charges. The binding of these polycations in w ater to a variety of polyanions was examined with respect to the effect of the 'spectator' counter cations on the observed association constants. The polycations precipitate ferri- and ferrocyanide, in some cases preferential ly for one oxidation state, and an X-ray crystallographic analysis of the c omplex between the tetracation 5 and ferricyanide reveals the complexity in volved even in the molecular recognition of small, charged compounds. (C) 2 000 Elsevier Science Ltd. All rights reserved.