Observation of polytypism among the hydroxysalts of Ni(II) and Co(II)

Layered hydroxysalts derive their crystal structure from mineral brucite. Nickel and cobalt based hydroxysalts with the composition M3(OH)4(NO3)2 crystallize in trigonal crystal system. On careful examination of the PXRD patterns, it is found that Ni3(OH)4(NO3)2 crystallizes in hexagonal crystal system while Co3(OH)4(NO3)2 crystallizes in rhombohedral crystal system. This clearly demonstrates that the crystal structures in layered hydroxysalts are mainly dictated by the nature of the cation occupying the preferential site within the layer.