Synthesis and structure refinement of layered double hydroxides of Co, Mg and Ni with Ga

摘要

Homogeneous precipitation by urea hydrolysis results in the formation of highly ordered layered double hydroxides of divalent metal ions (Co, Mg, Ni) and Ga. Structure refinement shows that these carbonate containing layered hydroxides crystallize with rhombohedral symmetry (space group R-3m) in the structure of the 3R_1 polytype. An analysis of the structure shows that, coulombic attraction between the layer and interlayer remains invariant in different layered hydroxides, whereas the strength of hydrogen bonding varies. The Ni-Ga LDH has the weakest hydrogen bonding and Co-Ga, the strongest, as reflected by the layer-interlayer oxygen-oxygen distances. The poor polarity of the OH bond in the Ni-Ga hydroxide points to the greater covalency of the (M~(2+)/M'~(3+))-oxygen bond in this compound as opposed to the Co-Ga hydroxide. These observations are supported by IR spectra.