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

Abstract

The centro symmetric dinuclear complex bis(μ-3-carboxy-6-methylpyridine-2-carboxylato)-κ3N,O2:O2;κ3O2:N,O2-bis[(2,2'-bipyridine-κ2N,N')(nitrato-κO)-cadmium] methanol monosolvate, [Cd2(C8H6NO4)2(NO3)2(C10H8N2)2]·CH3OH, was isolated as colourless crystals from the reaction of Cd(NO3)2·4H2O, 6-methylpyridine-2,3-dicarboxylic acid (mepydcH2) and 2,2'-bipyridine in methanol. The asymmetric unit consists of a CdII cation bound to a μ-κ3 N,O2:O2mepydcH- anion, an N, N'-bidentate 2,2'-bipyridine group and an O-monodentate nitrate anion, and is completed with a methanol solvent molecule at halfoccupancy. 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 CdII 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-κ3 coordination mode found in the title compound.