SAARBRUCKEN SERIES ON SUPRAMOLECULAR CHEM .36. THE INCREMENTAL DESCRIPTION OF HOST-GUEST COMPLEXES - FREE-ENERGY INCREMENTS DERIVED FROM HYDROGEN-BONDS APPLIED TO CROWN-ETHERS AND CRYPTANDS

The analysis of literature data for crown ether and cryptand-cation complexes with the principle of additive pairwise interactions yield excellent linear correlations between observed and calculated complex stabilities as long as geometric fit between ligand site and cation is present and no substantial strain is built up during complexation. These conditions are controlled partially by molecular mechanics simulations and partially by comparison to X-ray data. The cornerstone values used for each single ligand-cation interaction are taken from the electron donor parameters ED/Ci which have been derived earlier from over 900 hydrogen bond associations in carbon tetrachloride. The observed electron acceptor abilities EA of the different cations (alkali metal and ammonium ions) are a linear function of, e.g., hydration energies of these ions. Thus, a simple procedure is provided to calculate the stability of over 120 complexes on the basis of one EA parameter for each cation and only 11 ligand ED parameters (same for crowns and cryptands) which moreover are derived from independent sources and do not need to be adjusted.