Synthesis and Characterization of C-meso and C-racemic Isomers of a Reinforced Tetraaza Macrocycle and Their Copper(II) Complexes

摘要

Two isomers of a new tetraaza macrotricycle 2,2,4,9,9,11-hexaazamethyl-1,5,8,12-tetraazatricyclo[10.2.25.8]- octadecane (L2) containing additional N-CH2CH2-N linkages, C-meso-L2 and C-racemic-L2, have been prepared by the reaction of 1-bromo-2-chloroethane with C-meso-L1 or C-racemic-L1 (L1 = 5,5,7,12,12,14- hexamethyl-1,4,8,11-tetraazacyclotetradecane). Both C-meso-L2 and C-racemic-L2 react with copper(II) ion to form [Cu(C-meso-L2)]2+ or [Cu(C-racemic-L2)]2+ in dehydrated ethanol, but do not with nickel(II) ion under similar conditions. Crystal structure of [Cu(C-racemic-L2)(H2O)](ClO4)2 shows that the complex has distorted square-pyramidal coordination geometry with an apically coordinated water molecule. Unexpectedly, the Cu-N distances [2.016(3)-2.030(3) Å] of [Cu(C-racemic-L2)(H2O)](ClO4)2 are longer than those [1.992(3)- 2.000(3) Å] of [Cu(C-racemic-L1)(H2O)](ClO4)2. As a result, [Cu(C-racemic-L2)(H2O)]2+ exhibits weaker ligand field strength than [Cu(C-racemic-L1)(H2O)]2+. The copper(II) complexes readily react with CN- ion to yield the cyano-bridged dinuclear complex [Cu2(C-meso-L2)2CN]3+ or [Cu2(C-racemic-L2)2CN]3+. Spectra and chemical properties of [Cu(C-meso-L2)]2+ and [Cu2(C-meso-L2)2CN]3+ are not quite different from those of [Cu(C-racemic-L2)]2+ and [Cu2(C-racemic-L2)2CN]3+, respectively.