SYNTHESIS, CHARACTERIZATION AND BASICITY PROPERTIES OF 2 NEW OXA-AZA MACROBICYCLIC RECEPTORS - CRYSTAL-STRUCTURE OF A WATER-CRYPTATE

The synthesis and characterization of the two new oxa-aza macrobicycle s 16,21-dimethyl-4,7,10-trioxa-1, 3,16,21-tetraazabicyclo[11.5.5]trico sane (C1) and 19,24-dimethyl-4,7,10,13-tetraoxa-1,16,1 9,24-tetraazabi cyclo[14.5.5]hexacosane (C2) have been reported. Their proton transfer behaviour has been studied in aqueous solution by potentiometry (298. 1 +/- 0.1 K, / = 0.15 mol dm(-3)), microcalorimetry and H-1 and C-13 N MR spectroscopy. Both Of them behave as diprotic bases. C1 and C2 beha ve as strong bases in the first protonation step and as moderate bases in the second one. Their basicity is due to a main enthalpic contribu tion. NMR experiments indicate that the nitrogen atoms involved in the protonation steps are the methylated ones. The crystal structure of [ H(2)C2.H2O][ClO4](2) [space group P2(1), a = 10.450(2), b = 11.391(2), c 12.666(3) Angstrom, beta = 100.21(2)degrees, V = 1483.8(5) Angstrom (3), Z = 2, R = 0.059 and R(w) = 0.052] gives confidence to NMR result s, confirming that in the [H(2)C2.H2O](2+) cation the protons are loca lized on the methylated nitrogen atoms. Furthermore, a water molecule is enclosed into the macrocyclic cavity. interacting via hydrogen bond s with both protonated nitrogens and three oxygens of the macrocyclic framework and originating a 'water cryptate'.