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  Sci. Lett. J. 2012, 1: 26  
  Research Article
  Full Text
Hydrogen-bonded pillars of alternating chiral complex cations and anions: Synthesis, characterization and X-ray structure of isomorphous
catena-{(H3O)[K(H2O)3]@[Ni(H2oxado)3]2[Cr(C2O4)3]2.3H2O} and
catena-{(H3O)[Li(H2O)3]@[Ni(H2oxado)3]2[Cr(C2O4)3]2.3H2O}
 
  Y. A. Mbianguéa,b, J. Nenwaa, M. M. Bélombéa, J. Ngounec, E. Álvarezd  
     
a Inorganic Chemistry Department, Faculty of Science, P. O. Box 812, University of Yaounde I, Yaounde, Center Region, Cameroon
b Chemistry Department, Higher Teachers’ Training College, POB 55, University of Maroua, Cameroon.
c Department of Chemistry, Faculty of Science, University of Dschang, POB 67, Cameroon
d Instituto de Investigaciones Químicas - CSIC - Universidad de Sevilla, Avda. Américo Vespucio, 49, 41092 Sevilla, Spain

   
  Abstract  
  The familiar complex ions, [Ni(H2oxado)3]2+ (H2oxado = oxamide dioxime) and [Cr(C2O4)3]3-, self-assemble in weakly acidic aqueous medium in presence of group 1 metal cations to afford the isomorphous hydrogen-bonded coordination polymers of general formula catena-{(H3O)[MI(H2O)3]@[Ni(H2oxado)3]2 [Cr(C2O4)3]2.3H2O}, MI = K+ (1), Li+ (2). X-ray single crystal and powder diffraction techniques, together with elemental analysis and spectroscopic (FTIR/UV-Vis) characterizations, confirm the isomorphous nature of compounds 1 and 2. The structure of these materials consists of unfamiliar negatively charged infinite pillars of paramagnetic homo-chiral complex cations (2+ ) and anions (3- ), alternately stacked on top of each other along [100] and strongly interconnected by electrostatic and longitudinal O–H…O interactions. The average separation between next neighboring magnetic centers within a pillar is NiII…CrIII = 4.89 Å. Transversal hydrogen-bridgings between O and N atoms cross-link neighboring pillars of opposite chiralities (Δ vs Λ) and consolidate a negatively charged three-dimensional racemic host lattice framework which delineates two types of nanochannels parallel to the a axis. Small-size channels encapsulate K+ cations which are coordinated by O and N atoms from aqua, oxalato and oxamide dioxime ligands. Big-size channels host hydroxonium ions (H3O+) that are embedded amongst crystal water clusters, H-bonded to each other and to the organic ligands. Each excess negative charge unit within the host lattice framework of 1 is offset by a positive charge unit (0.5 H3O+ + 0.5 K+ ) lodged within the channels. The thermal stability of 1 was assessed by thermogravimetric analysis (TGA), and the effective magnetic moment measured at room temperature, reveals no perceptible coupling effect of the spins.  
     
  Keywords  
  Proton charge transfer; Nanochannel lattice; Negative complex pillars; H-bonded nickel-chromium complex polymer; Crystal structure; Protonized water clusters  
     
   
     
 
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