Cadmium(II) and copper(II) complexes with imidazole-containing tripodal polyamine ligands: pH and anion effects on carbon dioxide fixation and assembling

A new Cd(II) complex [Cd-3(L)(3)(mu(3)-CO3)](ClO4)(4)center dot 2CH(3)CN (1) with two- dimensional (2D) network structure was obtained by reaction of an imidazole-containing tripodal polyamine ligand N-1-(2-aminoethyl)-N1-(2-imidazolethyl)- ethane-1,2-diamine (L) with Cd(ClO4)(2)center dot 6H(2)O at pH 9.0 in air. The carbonate anions (CO32-) are from the hydration of the atmospheric carbon dioxide, which is the same as in the previously reported Cu(II) complex [Cu-3(L)(3)(mu(3)- CO3)]-(ClO4)(4)center dot 3CH(3)CN (2). However, the coordination mode of CO32- in 1 is mu(3)-eta(2):eta(2):eta(2) while the one in 2 is mu(3)-eta(1):eta(1):eta(1). One-dimensional (1D) chain Cd(II) and Cu(II) complexes [Cd(L)Cl] ClO4, H2O (3) and [Cu(L)(H2O)](ClO4)(2) (4) without CO32- were prepared by a similar method as that for 1 and 2 except for the different reaction pH, namely, 3 and 4 were obtained at pH 7 while 1 and 2 were obtained at pH 9. In addition, when Cu(NO3)(2) was used to react with L at pH 9, a unique 1D double-stranded helical chain complex [Cu(L)Cl]NO3 center dot 1.25H(2)O (5) was obtained. The results revealed that the reaction pH and the counteranion have great impact on the carbon dioxide absorption and hydration as well as on the assembling and structure of the complexes. The magnetic property of complex 2 was investigated in the temperature range of 1.8 - 300 K, and weak ferromagnetic coupling among the mu(3)-eta(1):eta(1):eta(1) CO32- bridged Cu(II) atoms was observed.