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 co mplexes with the principle of additive pairwise interactions yield exc ellent linear correlations between observed and calculated complex sta bilities as long as geometric fit between ligand site and cation is pr esent and no substantial strain is built up during complexation. These conditions are controlled partially by molecular mechanics simulation s and partially by comparison to X-ray data. The cornerstone values us ed for each single ligand-cation interaction are taken from the electr on donor parameters ED/Ci which have been derived earlier from over 90 0 hydrogen bond associations in carbon tetrachloride. The observed ele ctron 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 stab ility 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.