Anion mediated polytype selectivity among the basic salts of Co(II)

Abstract

Basic salts of Co(II) crystallize in the rhombohedral structure. Two different polytypes, 3R 1 and 3R 2 , with distinct stacking sequences of the metal hydroxide slabs, are possible within the rhombohedral structure. These polytypes are generated by simple translation of successive layers by (2/3, 1/3, z) or (1/3, 2/3, z). The symmetry of the anion and the mode of coordination influences polytype selection. Cobalt hydroxynitrate crystallizes in the structure of the 3R 2 polytype while the hydroxytartarate, hydroxychloride and a-cobalt hydroxide crystallize in the structure of the 3R 1 polytype. Cobalt hydroxysulfate is turbostratically disordered. The turbostratic disorder is a direct consequence of the mismatch between the crystallographically defined interlayer sites generated within the crystal and the tetrahedral symmetry of the SO 4 2À ions.

Polytypic transformations during the thermal decomposition of cobalt hydroxide and cobalt hydroxynitrate

“…Cobalt hydroxide and cobalt hydroxynitrate samples were prepared by following the procedure reported elsewhere [6,11]. Cobalt nitrate solution (1 M, 50 mL) was added to sodium hydroxide (2 M, 100 mL) solution at 80 1C.…”

“…Thermogravimetric studies were performed with a Mettler Toledo Model 851e TG/SDTA system (heating rate of 10 1C min À 1 under air from 25 to 650 1C. The wet chemical analysis of the samples was carried out following the procedure described elsewhere [11]. The chemical composition of cobalt hydroxide and cobalt hydroxynitrate are Co(OH) 2 and Co 2 (OH) 3 (NO 3 ), respectively.…”

“…In order to understand the phase evolution, X-ray powder diffraction patterns of cobalt hydroxide, cobalt hydroxynitrate with different type of polytypes and Co 3 O 4 were simulated by using the DIFFaX code. The details about the PXRD simulations have been explicitly defined in the literature [11,20]. In brief, the DIFFaX program enables us to simulate the PXRD pattern of crystalline solids.…”

“…Cobalt hydroxide and cobalt hydroxynitrate [Co 3 (OH) 4 (NO 3 ) 2 ] crystallizes in the mineral brucite structure [10,11].…”

Structural Synthon Approach to Predict the Possible Polytypes of Layered Double Hydroxides

“…The AC layer with the generalized composition [MX 2 ] is found in a very diverse range of materials such as metal sulfides MS 2 (M = Ti, Mo, Nb, Ta), [21,22] metal selenides MSe 2 (M = Mo, Ta), [23] divalent halides MX 2 (M = Ca, Mg, Fe, Co, Ni, Cd), [24,25] metal hydroxides M(OH) 2 (M = Mg, Ni, Co), [26,27] birnessite-type oxides MO 2 (M = Mn), [28,29] lithium oxides LiMO 2 [30,31] and basic salts M(OH) 2-x A x (M = Ni, Co; x = 0.66-0.25; A = Cl, NO 3 ). [32][33][34] We therefore call the AC layer a 'structural synthon', the term "structural" is used to describe the extended nature of the AC layer, as opposed to the sub.-molecular synthon originally proposed by Corey [35] and the supramolecular synthon of Desiraju [36,37] which are entities of finite dimension. In this paper, apart from the robust ubiquity we further propose that the structural synthon is characterized by its symmetry.…”