BINUCLEAR COPPER(II) COMPLEXES OF BIS(1,4,7-TRIAZACYCLONONANE) LIGANDS CONTAINING TRIMETHYLENE AND TETRAMETHYLENE BRIDGING GROUPS - AN EQUILIBRIUM AND STRUCTURAL STUDY

Two members of a homologous series of bis(triazacyclononane) Ligands, 1,3-bis(1,4,7-triaza-1-cyclononyl)propane, EM3, and 1,4-bis(1,4,7-tria za-1-cyclononyl)butane, EM4, form stable 1:1 and 2:1 Cu(II)-L complexe s. Dissociation constants for the acid salts of the compounds and equi librium studies with copper(II) in aqueous 0.1 M KNO3 at 25 degrees C an reported. Cu(EM3)(2+) is more stable than Cu(EM4)(2+) while Cu-2(EM 4)(4+) is slightly more stable than Cu-2(EM3)(4+). Probable reasons fo r this behavior are discussed in light of the 1:1 complexes existing i n solution as monomeric species. Binuclear copper(II) complexes of eac h ligand have been isolated and their structures determined by X-ray c rystallography. Cu-2(EM3)Cl-4 . 2H(2)O crystallizes in space group P2/ c with unit cell dimensions a = 12.607(3) Angstrom, b = 7.589(2) Angst rom c = 12.948 Angstrom, and beta = 93.71(3)degrees. Cu-2(EM4)Cl-4 cry stallizes in space group P2(1)/c with unit cell dimensions a = 11.919( 2) Angstrom, b = 8.468(2) Angstrom, c = 11.508(2) Angstrom, and beta = 99.06(3)degrees. In both complexes the copper(II) is 5-coordinate wit h two secondary amine N atoms of a [9]aneN(3) group and two Cl- occupy ing sites at the base and the tertiary N atom of the same moiety at th e apex of a square pyramid. The structures have somewhat different con formations. The pair of Cl- attached to the two Cu(II) are approximate ly syn for Cu-2(EM3)Cl-4 . 2H(2)O and anti for Cu-2(EM4)Cl-4.