One-dimensional pyrazine bridged M(II)-saccharinato coordination polymers: Synthesis, characterization, crystal structures and thermal studies

Three new coordination polymers with a general formula [M(sac)2(μ-pyz)(H2O)2]n [M = Mn(II) (1), Fe(II) (2), Co(II) (3), pyz = pyrazine, and sac = saccharinate] have been synthesized and characterized by elemental analyses, IR, UV–VIS, magnetic measurements, thermal analysis techniques and single crystal X-ray diffraction. All three complexes are isomorphous, crystallizing in the triclinic space group P1¯ (No. 2). Each metal(II) ion in 1–3 is octahedrally coordinated by two sac, two pyz and two aqua ligands. The sac ligands are N-coordinated, while the pyz ligands bridge the metal centers leading to an one-dimensional linear chain structure. Intra-chain M–M separations in complexes 1, 2 and 3 are 7.381(2), 7.259(3) and 7.188(3) Å, respectively. The individual chains are linked into two-dimensional layers by O–H⋯O hydrogen bonds involving the hydrogens of aqua ligands and carbonyl and sulfonyl O atoms of sac ligands. The hydrogen bonded layers are further assembled into three-dimensional supramolecular networks by weak aromatic π⋯π stacking interactions between the phenyl rings of sac ligands or CH⋯π interactions involving pyz. These complexes exhibit similar decomposition characteristics. In the first stages, endothermic removal of the aqua and pyz ligand takes place leading to an intermediate probably in the form of [M(sac)2], which undergoes highly exothermic decomposition at higher temperatures to give corresponding metal oxides.

The reaction of [M(sac)2(H2O)4] · 2H2O, where M is Mn(II), Fe(II), and Co(II), and sac is the saccharinate anion, with pyrazine (pyz) result in the formation of the corresponding coordination polymers [M(sac)2(μ-pyz)(H2O)2]n. The pyz ligands bridge the metal centers leading to an one-dimensional linear chain. The chains are linked into 2D layers by hydrogen bonds and the 2D layers are further arranged into three-dimensional supramolecular networks by weak π⋯π and CH⋯π interactions.Figure optionsDownload as PowerPoint slide