Scientific publications
Michel M. Bélombé
Other affiliations: Laboratoire de Chimie
Justin Nenwa
Other affiliations: Laboratoire de Chimie
N.A.S.N. Tchuisse
Other affiliations: Laboratoire de Chimie
Franziska Emmerling
S. Obbade
Boniface P. T. Fokwa
A. Semmoud
HAL (Le Centre pour la Communication Scientifique Directe)
The novel coordination polymer of general formula {[(H<sub>2</sub>O)Ba(<i>μ</i>-H<sub>2</sub>O)Ba(OH<sub>2</sub>)<sub>4</sub>]@ [(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Al(<i>μ</i>-OH)<sub>2</sub>Al(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>].H<sub>2</sub>O}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 <i>μ</i>-bridge neighboring Ba(II) and Al(III) centers. The asymmetric unit of 1 consists of one cationic tri-<i>μ</i>-oxygen-bridged pseudo-dimer - formally [(H<sub>2</sub>O)Ba1(μ-H<sub>2</sub>O)Ba2(OH<sub>2</sub>)<sub>4</sub>]<sup>4+</sup> - one centrosymmetric anionic di-<i>μ</i>-hydroxido-bis[<i>cis</i>-bis(oxalato)aluminate] dimer - [(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Al1(<i>μ</i>-OH) <sub>2</sub>Al2(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>]<sup>4-</sup> - and one solvent water molecule. The Ba<sup>2+</sup> ions in the cationic dimer are both ten-coordinate and 4.335(1) Å apart. The Al<sup>3+</sup> 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 <i>P</i>2<sub>1</sub>/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 <i>via</i> 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.
