BINUCLEAR COPPER(II) COMPLEXES OF BIS(1,4,7-TRIAZACYCLONONANE) LIGANDS CONTAINING TRIMETHYLENE AND TETRAMETHYLENE BRIDGING GROUPS - AN EQUILIBRIUM AND STRUCTURAL STUDY
Xp. Zhang et al., BINUCLEAR COPPER(II) COMPLEXES OF BIS(1,4,7-TRIAZACYCLONONANE) LIGANDS CONTAINING TRIMETHYLENE AND TETRAMETHYLENE BRIDGING GROUPS - AN EQUILIBRIUM AND STRUCTURAL STUDY, Inorganic chemistry, 34(11), 1995, pp. 2883-2888
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.