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Modulation of a Supramolecular Bowl and Pot by Changing Solvent Systems and/or Metal/Ligand Ratios
Author(s) -
Park Seong Jin,
Lee Jae Woo,
Sakamoto Shigeru,
Yamaguchi Kentaro,
Hong JongIn
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390203
Subject(s) - supramolecular chemistry , isothermal titration calorimetry , chemistry , ligand (biochemistry) , solvent , metal ions in aqueous solution , aqueous solution , titration , metal , hydrogen bond , crystallography , enthalpy , inorganic chemistry , crystal structure , organic chemistry , molecule , biochemistry , physics , receptor , quantum mechanics
A resorcin[4]arene‐based ligand 2 a with four pyrimidine substituents at the upper rim was synthesized, and the generation of different metal‐mediated superstructures from the same ligand and metal ions utilizing the unfavorable incorporation of the third and fourth Pd II ions to ligand 2 a was investigated. The supramolecular bowl 3 a , which comes from a 1:2 combination of ligand 2 a and [Pd(en)(NO 3 ) 2 ], was obtained in water even though excess of Pd II complexes were employed. By adding methanol, the supramolecular pot 4 gradually formed, which was the major product when the ratio of mixed solvent reached methanol/water=5:1 (v/v). Host–guest complexation phenomena of 3 a toward several aromatic carboxylates were demonstrated by isothermal titration calorimetry (ITC) and by 1 H NMR spectroscopy; both the enthalpy gain from electrostatic and hydrophobic interactions, and the entropy gain from desolvation cooperatively contribute to the binding of anionically charged guests. The crystal structure of supramolecular pot 4 shows direct evidence for the hydrogen bonding between water and the aromatic π electrons in the solid state. The modulation between supramolecular bowl 3 a and pot 4 was also made possible by changing the metal/ligand ratios in aqueous methanol solution as well as by varying the water content of the mixed solvent.