THERMODYNAMIC, SPECTROSCOPIC, AND STRUCTURAL STUDIES OF COMPLEXATION OF PHENOL-ARMED AND PYRIDINE-ARMED MACROCYCLIC LIGANDS WITH UNIVALENT METAL-IONS

Log K, Delta H, and Delta S values for interactions of a series of pyr idinoazacrown ethers each bearing a phenol arm (2-6) and two macrocycl es each bearing a pyridine arm (7, 8) with Na+, K+, Tl+, and Ag+ have been determined in absolute methanol at 25 degrees C by calorimetric t itration. In each case, the complex stability has the sequence Naf < K + < Tl+ much less than Ag+. The phenol-armed macrocycles exhibit selec tivity of more than 4 orders of magnitude for Ag+ over Na+, K+, and Tl +. Attachment of a pendant phenol arm having various substituents to p arent macrocycle 1 increases the binding abilities of the resulting li gands. Substituents on the para position of the phenol arm have an app reciable effect on cation-binding constants. Good Hammett correlations are found by plotting log K values vs sigma(p) for interactions of fi ve phenol-armed macrocyclic ligands (2-6) with Na+, K+, and Tl+. The c omplexation has been characterized by means of H-1 NMR and UV-visible spectroscopic, and X-ray crystallographic methods. The crystal data fo r Na+-3: formula, [Na(C23H28.5N3O5)](ClO4)(0.5); space group, P (1) ov er bar; a = 9.400(9) Angstrom, b = 11.467(10) Angstrom, c = 12.281(11) Angstrom, alpha = 77.22(7)degrees, beta = 87.73(7)degrees, gamma = 86 .39(7)degrees, V = 1288(2) Angstrom(3), and Z = 2. The study indicates that the phenol OH group of 2-6 is capable of forming an intramolecul ar hydrogen bond with the macroring nitrogen atom and that the complex ation in absolute methanol generally does not deprotonate these phenol s. In the crystal structure of the Na+-3 complex, the Na+ is coordinat ed to all seven of the donor atoms of the ligand and two Na+-3 complex es join together to form a dimer. The dimer contains an intermolecular hydrogen bond formed between the phenol hydrogen atom of one ligand a nd the phenolate group of a centrosymmetrically related ligand and two pi-pi stacking interactions between the electron-deficient pyridine r ing of one molecule and the electron-rich phenol ring of the other.