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  Sci. Lett. J. 2012, 1: 24  
  Research Article
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Synthesis, crystal structure and thermal stability of the novel coordination polymer of general formula: {[(H2O)Ba(μ-H2O)Ba(OH2)4]@[(C2O4)2Al(μ-OH2Al(C2O4)2].H2O}n  
  Michel M. Bélombéa, Justin Nenwaa, Narcisse A. S. N. Tchuissea, Franziska Emmerlingb, Saïd Obbadec, Ahmed Semmoudc, Boniface P. T. Fokwad  
a Inorganic Chemistry Department, Coordination Chemistry Laboratory, Faculty of Science, P. O. Box 812, University of Yaounde 1, Yaounde, Cameroon
b Bundesanstalt für Materialforschung und -prüfung, Richard-Willstätter-Str. 11, D-12489 Berlin-Adlershof, Germany
c Chemistry Department, University of Science and Technology, Lille 1, France
d Institute of Inorganic Chemistry, RWTH Aachen University, 52056 Aachen, Germany

  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.  
  Nonmolecular coordination polymer; Aluminum oxalato dimer; Barium pseudo-dimer; Negative complex pillars; Internetting bridge; Crystal structure  
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