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...O hydrogen bonds to form a three-dimensional hydrogen-bonded framework structure. Each of the ions in hydrazinium(2+) diaqua(4-oxo-4H-pyran-2,6-dicarboxylato)calcate, (N(2)H(6))[Ca(C(7)H(2)O(6))2(H2O)2], (II), lies on a twofold rotation axis in the space group P2/c; the anions form hydrogen-bonded sheets which are linked into a three-dimensional framework by the cations. In bis(mu-4-oxo-4H-pyran-2,6-dicarboxylato)bis[tetraaquamanganese(II)] tetrahydrate, [Mn2(C(7)H(2)O(6))2(H2O)(8)].4H2O, (III), the metal ions and the organic ligands form a cyclic centrosymmetric Mn2(C(7)H(2)O(6))2 unit, and these units are linked into a complex three-dimensional framework structure containing 12 independent O-H...O hydrogen bonds. There are two independent Cu(II) ions in tetraaqua(4-oxo-4H-pyran-2,6-dicarboxylato)copper(II), [Cu(C(7)H(2)O(6))(H2O)4], (IV), and both lie on centres of inversion in the space group P1; the metal ions and the organic ligands form a one-dimensional coordination polymer, and the polymer chains are linked into a three-dimensional framework containing eight independent O-H...O hydrogen bonds. Diaqua(4-oxo-4H-pyran-2,6-dicarboxylato)cadmium monohydrate, [Cd(C(7)H(2)O(6))(H2O)2].H2O, (V), forms a three-dimensional coordination polymer in which the organic ligand is coordinated to four different Cd sites, and this polymer is interwoven with a complex three-dimensional framework built from O-H...O hydrogen bonds.