Synthesis, crystal structures and lithium encapsulation by some phenolic aza cages

Three new macrocyclic cages 1, 2 and 3, able to selectively encapsulate the lithium ion, were studied. The synthesis and characterization of 2 and 3 a re reported. The basicity behaviour of the three cages was investigated by spectrophotometry and by H-1 and C-13 NMR spectroscopy. The protonation con stants were determined by potentiometric methods in aqueous solution (I = 0 .15 mol dm(-3) NMe4Cl, T = 298 +/- 0.1 K) and were found to be logK(1) = 11 .67(5), 10.77(7), 11.17(7); logK(2) = 7.76(5), 5.7(1), 5.6(1); logK(3) = 1. 3(1), 2.4(1), 1.9(1) for 1, 2, and 3, respectively. The lithium equilibrium complex formation Li+ + L = LiLH-1 + H+ was monitored by C-13 and Li-7 NMR spectroscopy, as well as by spectrophotometric and potentiometric techniqu es; log values of -9.1(1) and -8.0(1) were found for 1 and 3, respectively. For 2, precipitation of the lithium complex occurs. UV/Vis studies in aque ous solution show a significant shift towards high energy of the lambda(max ) in the lithium complex, indicating the potential for application of these ligands in colourimetric analysis, The crystal structure of 1 was examined by single crystal X-ray diffraction, Data collection was performed on two samples, namely la and Ib, obtained from two different crystallization proc edures. Crystals of la are monoclinic, space group P2(1)/n, while 1b crysta llized in an orthorhombic space group Pc2(1)b. The cell parameters are a = 12.423(3), b = 14.378(9), c = 28.436(7) Angstrom, beta = 93.74(2)degrees fo r 1a, and a = 10.674(4), b = 14.408(2), c = 17.034(2) Angstrom for 1b. Mole cular simulations were carried out on both conformational isomers la and Ib , with results indicating that the two isomers have essentially the same fl exibility.