Synthesis and ligational behavior toward hydrogen and copper(II) ions of the two new oxa-aza macrocyclic receptors 10,13,16-trimethyl-1,4-dioxa-7,10,13,16,19-pentaazacyclohenicosane (Me3[21]aneN5O2) and 13,16,19-trimethyl-1,4,7-trioxa-10,13,16,19,22-pentaazacyclotetracosane (Me3[24]aneN5O3)

The synthesis and characterization of the two new oxa-aza macrocycles 10,13,16-trimethyl-1 ,4-dioxa- 7,10,13,16,19-pentaazacyclohenicosane (Me3[21 laneN~0~) and 13,16,19-trimethyl- 1,4,7-trioxa-l0,13,16,19,22- pentaazacyclotetracosane (Me3[24]aneN~Os) are reported. Their basicity behavior in aqueous solution was investigated by means of potentiometric (298.1 f 0.1 K, Z = 0.15 mol dm-3) and NMR (1H and W) techniques. 1HJH and 1H-13C two-dimensional NMR experiments permitted the unequivocal assignment of all IH and 13C resonances. Both of them behave as tetraprotic bases under the experimental conditions used. The protonation mechanism of these macrocyclic ligands was determined by means of 'H and I3C NMR spectra at various pH values. The thermodynamic parameters for the formation of 1:l copper(I1) complexes of both macrocycles were determined by potentiometry and microcalorimetry at 298.1 f 0.1 K in 0.15 mol dm-3 NaC104. The involvement of all nitrogen donor atoms of the macrocycles in the coordination of the metal ion can be deduced, while the oxygens remain unbound. Furthermore mono- and diprotonated species are present at low pH. Crystal and molecular structures of the complexes [Cu(Me3[ 24IaneNsO3)l (C104)2 and [Cu(H2Me3[2 l]aneN502)C12] (C104)2.2H20 were determined by single-crystalX-rayanalysis. In [Cu(Me3[24]aneN~O~)](ClO~)~ (spacegroupP21, a = 8.371(2) A, b = 11.781- (2) A, c = 14.390(3) A, B = 96.90(2)", V= 1408.8(5) A3, Z = 2, R = 0.047, R, = 0.045) the metal ion is bound by the five nitrogens of the macrocyclic ligand, in a distorted square-pyramidal coordination geometry. In [Cu- (HzMe~[21]aneNsO~)Clz](C1O4)~2H~0 (space group Pi, a = 10.999(6) A, b = 11.066(8) A, c = 14.71(1) A, a = 81.77(6), 0 = 80.46(5), y = 61.68(5)O, V= 1550(2) A3, Z = 2, R = 0.052, R, = 0.047) the copper(I1) ion is coordinated by the three methylated nitrogen atoms of the ligand and two chloride anions, while the uncoordinated nitrogens are protonated. The resulting coordination polyhedron can be described as a trigonal bipyramid distorted toward a square pyramid with elongated axial distances. The latter crystal structure can give information on the topological features of protonated complexes of polyaza macrocyclic ligands.