Cationic, neutral and anionic metal(II) complexes derived from 4-oxo-4H-pyran-2,6-dicarboxylic acid (chelidonic acid).

The structures of five metal complexes containing the 4-oxo-4H-pyran-2,6-dicarboxylate dianion illustrate the remarkable coordinating versatility of this ligand and the great structural diversity of its complexes. In tetraaquaberyllium 4-oxo-4H-pyran-2,6-dicarboxylate, [Be(H(2)O)(4)](C(7)H(2)O(6)), (I), the ions are linked by eight independent O-H..