Six-, seven- and eight-coordinated Cd(II) ions with N-heterocyclic multicarboxylic acids

Two novel cadmium complexes [Cd3(pta)2(H2O)4]n (1) (H3pta = 2,4,6-pyridinetricarboxylic acid) and {[Cd(H2pza)(H2O)2] · 2H2O}n (2) (H4pza = 2,3,5,6-pyrazinetetracarboxylic acid) were synthesized. In both complexes, Cd(II) ions show three different coordination numbers of six and seven in 1 and eight in 2, respectively. Complex 1 displays a three-dimensional network structure and 2 shows a one-dimensional chain structure. The one-dimensional chains in 2 are vertical or parallel to each other and form a three-dimensional network structure by hydrogen bonds. In addition, 1 emits intense fluorescence on excitation of 342 nm.

Cd(II) ions in two complexes with 2,4,6-pyridinetricarboxylic acid and 2,3,5,6-pyrazinetetracarboxylic acid showed three different coordination numbers of six, seven and eight, respectively. The unusual high coordination numbers were rare to be found in transition metal ions.Figure optionsDownload as PowerPoint slide