Synthesis and crystal structure of Co_2(OH)_2CO_3 by Rietveld method

摘要

A new cobalt hydroxide carbonate Co_2(OH)_2CO_3 was successfully synthesized by a hydrothermal method. The compound is isomorphous with malachite [Cu_2(OH)_2CO_3] and crystallizes in a monoclinic system [space group P2_1/a (No. 14); a = 9.448(5) A, b= 12.186(9) A, c = 3.188(4) A, β= 98.593°, V= 367.143(9) A~3, Z=4, and Dc = 3.786(9) g/cm~3]. Crystal structure of Co_2(OH)_2CO_3 was refined by the Rietveld method with R_P=43%, R_(WP)=5.7%, R_(exp)-5.1%, R_B = 1.74%, and S= 1.117 on the basis of the X-ray powder diffraction data. The crystal structure of Co_2(OH)_2CO_3 obtained by the Rietveld refinement shows that all species Co_(2+), CO_3~(2-) , and OH~-ions occupy C_1 site symmetry. Two crystallographically different Co_(2+) and OH~- ions and one type CO_3~(2-) ion exist in the lattice. Co(1) is coordinated to two oxygen atoms from CO_3~(2-) ions and two OH" ions; Co(2) is coordinated to two oxygen atoms from CO_3~(2-) ions and four OH" ions, thus forming a distorted octahedron with (4 + 2) coordination.