Synthesis, crystal structure and thermal stability of the novel coordination polymer of general formula: {[(H₂O)Ba(<i>μ</i>-H₂O)Ba(OH₂)₄]@[(C₂O₄)₂Al(<i>μ</i>-OH)₂Al(C₂O₄)₂].H₂O}n^§

Abstract

The novel coordination polymer of general formula {[(H2O)Ba(μ-H2O)Ba(OH2)4]@ [(C2O4)2Al(μ-OH)2Al(C2O4)2].H2O}n (1), has been synthesized in water and characterized by FTIR spectra, elemental and thermal analyses, and by full X-ray structure determination. Compound 1 crystallizes in an interesting nonmolecular coordination network where oxalato ligands μ-bridge neighboring Ba(II) and Al(III) centers. The asymmetric unit of 1 consists of one cationic tri-μ-oxygen-bridged pseudo-dimer - formally [(H2O)Ba1(μ-H2O)Ba2(OH2)4]4+ - one centrosymmetric anionic di-μ-hydroxido-bis[cis-bis(oxalato)aluminate] dimer - [(C2O4)2Al1(μ-OH) 2Al2(C2O4)2]4- - and one solvent water molecule. The Ba2+ ions in the cationic dimer are both ten-coordinate and 4.335(1) Å apart. The Al3+ ions in the anionic dimer each experience distorted octahedral coordination by six O atoms, being distant by 2.854 Å in average and centered at two independent lattice positions related by the P21/n space group symmetry. The anionic dimers are interconnected amongst themselves via O-H***O bridgings across the hydroxido groups into 1-D pillars that run parallel to [001]. These negatively charged pillars are tightly cross-linked via coordinate bonds of oxalato O atoms to the cationic Ba dimers. Coulombic interactions between the ionic motifs and extended 3-dimensional H-bonding involving solvent water molecules as well, concur to consolidate the bulk structure. Thermogravimetric analysis (TGA) shows that compound 1 is stable to heat up to 400 °C