Isotypic Mn(II) and Fe(II) binuclear complexes of the ligand 5,6-bis-(pyridin-2-yl)-pyrazine-2,3-di-carb-oxy-lic acid.

The title isotypic complexes, bis-[μ-5,6-bis-(pyridin-2-yl)pyrazine-2,3-di-carboxylato]-κ(4)N(1),O(2),N(6):O(3);κ(4)O(3):N(1),O(2),N(6)-bis-[di-aqua-manganese(II)] tetra-hydrate, [Mn2(C16H8N4O4)2(H2O)4]·4H2O, (I), and bis-[μ-5,6-bis-(pyridin-2-yl)pyrazine-2,3-di-carboxyl-ato]-κ(4)N(1),O(2),N(6):O(3);κ(4)O(3):N(1),O(2),N(6)-bis-[di-aqua-iron(II)] tetrahydrate, [Fe2(C16H8N4O4)2(H2O)4]·4H2O, (II), are, respectively, the mangan-ese(II) and iron(II) complexes of the ligand 5,6-bis-(pyridin-2-yl)-pyrazine-2,3-di-carb-oxy-lic acid. The complete mol-ecule of each complex is generated by inversion symmetry. Each metal ion is coordinated by a pyrazine N atom, a pyridine N atom, two carboxyl-ate O atoms, one of which is bridging, and two water O atoms. The metal atoms have MN2O4 coordination geometries and the complexes have a cage-like structure. In the crystals of both compounds, the complexes are linked by O-H⋯O and O-H⋯N hydrogen bonds involving the coordinating water mol-ecules, forming chains along [100]. These chains are linked by O-H⋯O hydrogen bonds involving the non-coordinating water mol-ecules, forming layers parallel to (011). The layers are linked by pairs of C-H⋯O hydrogen bonds and offset π-π inter-actions, so forming a hydrogen-bonded three-dimensional framework.