Structure of the Molecular Receptor 1,4,7,10-Tetrakis [(S)-2-hydroxy-2-phenylethyl]-1,4,7,10-tetraazacyclododecane:A Combined X-Ray Crystallographic and Theoretical Study Producing an Assessment of the Crystal Packing Energy

摘要

X-Ray crystallography demonstrates that the guest molecule binding cavity within the molecular receptor ligand 1,4,7,10-tetrakis[(S)-2-hydroxy-2-phenylethyl]-1,4,7,10-tetraazacyclododecane,(S)-thpec12,is a poorly defined conical region stabilized by three O-H...O hydrogen bonds and a single O-H...N hydrogen bond.Two similar,but crystallographically independent,molecules exist within the unit cell.Ab initio calculations,using Gaussian 03 (LanL2DZ basis set at the Hartree-Fock level of theory),predict that these have steric energies of 97.73 and 97.06 kJ mol~(-1),respectively,above that of the minimum energy (gas phase) conformer of the same hydrogen-bonding configuration,which is believed to be the structure of global minimum energy.The mean of these energies (97.4 kJ mol~(-1)) represents a best estimate of the crystal packing energy for (S)-thpec 12,some of which is seen to be expended in rotating the phenyl rings away from the positions favoured in the gas phase.The ability of the Cd~(II) complex of (S)-thpec12 to act as a molecular receptor for aromatic anions is demonstrated by the isolation of two inclusion compounds in which p-nitrophenolate and anthraquinone-2-sulfonate are retained.