Synthesis and Complexing Properties of the Large Polyazacycloalkane 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane (l) - Crystal-structure of the Monoprotonated Dicopper(ii) Complex [cu2(l)hcl2](clo4)3.4h2o

The synthesis and characterization of the large am macrocycle 1,4,7,10,13,16,19,22,25,28-decaamcyclotriaconta(Lne) ([30]aneNlo) are described. Crystals of the com ound [CU~(L)HCI~](CIO~a)re~ m-o~nHoc~liOni c, space group P2/n, with a = 21.491 (5) A, b = 7.696 (4) A, c = 12.210 (4) 1,le = 103.04 (5)O, and 2 = 2. Refinement of the atomic parameters by least-squares methods gave a final R factor of 0.097 (R, = 0.097) for 1298 unique reflections with I > 3 4 ) . The structure consists of binuclear [Cu2(L)HCl2I3' cations and perchlorate anions; each half of the macrocycle is symmetry related by a twofold axis passing through its center. The cop r atoms (CuCu distance 7.26 (1) A) are coordinated by four nitrogen atoms of the macrocycle ligand (average Cu-N = 2.03 (2) 6 and one chloride ion (CuCI = 2.43 (1) A) in a square-pyramidal geometry. One of the two uncoordinated nitrogen atoms is protonated. The basicity constants of the macrocycle and the stability constants of the copper(I1) complexes were determined by potentiometry at 25 OC in 0.15 mol dm-3 NaC104 The formation enthalpy of the species [Cu2(L)I4' was determined by batch microcalorimetry. Only binuclear species are formed; the stability of the binuclear [Cu2(L)I4' species is high (log K = 37.77), and its formation is largely exothermic (AHo = -45.5 kcal mol-'). The thermodynamic quantities AGO and AHo as well as the electronic spectral features of the [Cu2(L)I4' species indicate that all nitrogen atoms are coordinated to the copper(I1) atoms. The [CU,(L)]~' macrocycle shows a great tendency to form protonate