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.

Graphical abstractCd(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 full-size imageDownload as PowerPoint slide