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 [Cd3(L)3(μ3-CO3)](ClO4)4·2CH3CN (1) with two-dimensional (2D) network structure was obtained
by reaction of an imidazole-containing tripodal polyamine ligand N1-(2-aminoethyl)-N1-(2-imidazolethyl)-ethane-1,2-diamine (L) with Cd(ClO4)2·6H2O 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 [Cu3(L)3(μ3-CO3)](ClO4)4·3CH3CN (2). However, the coordination mode of CO32- in 1 is μ3-η2:η2:η2 while the one in 2 is μ3-η1:η1:η1. 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]NO3·1.25H2O (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 μ3-η1:η1:η1−CO32- bridged Cu(II) atoms was observed.