Transformation of the structure in a series of mixed K$_2$Ni$_x$Co$_{1-x}$(SO$_4)_2\cdot6$H$_2$O single crystals

The structure of crystals of solid solutions K$_2$Ni$_x$Co$_{1-x}$(SO$_4)_2\cdot6$H$_2$O has been studied. The substitution of nickel atoms for cobalt atoms in the K$_2$Co(SO$_4)_2\cdot6$Н$_2$О structure leads to a decrease in all interatomic distances (Co,Ni)–O. However, the decrease in one of them with the increase in the Ni concentration is smaller than that in the other two. As a consequence, CoO$_6$ octahedra are more distorted than NiO$_6$. Syntheses of the difference electron density show that the structures of crystals of solid solutions K$_2$Co(SO$_4)_2\cdot6$H$_2$O contain more uninterpreted peaks of the residual electron density than the K$_2$Ni(SO$_4)_2\cdot6$H$_2$O structure, indicating a change in the character of the hydrogen bond.