Comparative study on Cd(II) and Ca(II) model complexes with pyridine-2,3-dicarboxylic acid: Synthesis, crystal structure and spectroscopic investigation

Two novel cadmium and one calcium complex, in which pyridine-2,3-dicarboxylic acid (2,3pydcH2) acts as a monodicarboxylate anion (2,3pydcH) with one acid hydrogen on the hetero-nitrogen or a doubly deprotonated dicarboxylate anion (2,3pydc), have been synthesized and characterized using single crystal X-ray diffraction, elemental analysis and IR, Raman, 1H and 13C NMR spectroscopies: [Cd(2,3pydcH)3][Cd(H2O)6]0.5 (1), [Cd(2,3pydc)(H2O)3]n (2), [Ca(2,3pydcH)2(H2O)3]n (3). Complex 1 crystallizes in the trigonal system space group P  3¯. The cadmium anion Cd(1) {CdN3O3} and cation Cd(2) (coordinated by 6 water molecules) possess the same coordination polyhedra (octahedral). Packing analysis reveals that complex 2 (space group Pca21) has a very interesting coordination network. The column of 21 symmetry is built up of translationally repeated mer units, [–O–Cd(3H2O)C7NO3–O–]n, arranged into two dimers rotated relative to each other by 180° (a twisted zigzag screen). Polymeric complex 3 crystallizes in the monoclinic system (space group P21/c). Two molecules of ligand and three molecules of water are bounded directly to the metal ion to give a {CaNO7} chromophore, which results in coordination polyhedron described as a pseudo-dodecahedron. It is worth noticing that two types of coordination modes of the 2,3pydcH ligand exist in the structure: one of them acts as chelating (N,O) bidentate ligand in which the carboxyl groups are bound to each other by a very short strong hydrogen bond (O(9)⋯O(12)); the other acts as tridentate (O, O, O′) coordinating anion with one acid hydrogen attached to the nitrogen atom.

Two novel cadmium and one calcium complex in which pyridine-2,3-dicarboxylic acid (2,3pydcH2) acts as a monodicarboxylate anion (2,3pydcH) or a doubly deprotonated dicarboxylate anion (2,3pydc) have been synthesized and characterized using single crystal X-ray diffraction, elemental analysis and IR, Raman, 1H and 13C NMR spectroscopies: [Cd(2,3pydcH)3][Cd(H2O)6]0.5 (1), [Cd(2,3pydc)(H2O)3]n (2), [Ca(2,3pydcH)2(H2O)3]n (3).Figure optionsDownload as PowerPoint slide