Structure of a dinuclear cadmium complex with 2,2′-bi­pyridine, monodentate nitrate and 3-carb­oxy-6-methyl­pyridine-2-carboxyl­ate ligands: intra­molecular carbon­yl(lone pair)⋯π(ring) and nitrate(π)⋯π(ring) inter­actions

The centrosymmetric dinuclear complex bis­(μ-3-carb­oxy-6-methyl­pyridine-2-carboxyl­ato)-κ(3) N,O (2):O (2);κ(3) O (2):N,O (2)-bis­[(2,2′-bi­pyridine-κ(2) N,N′)(nitrato-κO)cadmium] methanol monosolvate, [Cd(2)(C(8)H(6)NO(4))(2)(NO(3))(2)(C(10)H(8)N(2))(2)]·CH(3)OH, was isolated as colourless crystals from the reaction of Cd(NO(3))(2)·4H(2)O, 6-methyl­pyridine-2,3-di­carb­oxy­lic acid (mepydcH(2)) and 2,2′-bi­pyridine in methanol. The asymmetric unit consists of a Cd(II) cation bound to a μ-κ(3) N,O (2):O (2)-mepydcH(−) anion, an N,N′-bidentate 2,2′-bi­pyridine group and an O-mono­dentate nitrate anion, and is completed with a methanol solvent mol­ecule at half-occupancy. The Cd complex unit is linked to its centrosymmetric image through a bridging mepydcH(−) carboxyl­ate O atom to complete the dinuclear complex mol­ecule. Despite a significant variation in the coordination angles, indicating a considerable departure from octa­hedral coordination geometry about the Cd(II) atom, the Cd—O and Cd—N distances in this complex are surprisingly similar. The crystal structure consists of O—H⋯O hydrogen-bonded chains parallel to a, further bound by C—H⋯O contacts along b to form planar two-dimensional arrays parallel to (001). The juxtaposed planes form inter­stitial columnar voids that are filled by the methanol solvent mol­ecules. These in turn inter­act with the complex mol­ecules to further stabilize the structure. A search in the literature showed that complexes with the mepydcH(−) ligand are rare and complexes reported previously with this ligand do not adopt the μ-κ(3) coordination mode found in the title compound.