The name Nickelbischofite (NiCl2•6(H2O)) suggests that it is merely Bischofite (MgCl2•6(H2O)) with nickel replacing magnesium. Indeed, nickel and magnesium are well known as geochemical twins because of the similar sizes and charges on the cation, even though the elements are completely different in their test tube chemistry. However, nickelbischofite is significantly different from bischofite. To begin with,, its unit cell is considerably more oblique. Even more significantly, the octahedra around the calcium ions in bischofite are made entirely of water, with chlorine between the octahedra. In nickelbischofite, chlorine atoms are at opposite ends of each octahedron. The orphaned water molecules float as disembodied wraiths in the void between the octahedra.
Below is one layer of the nickelbischofite structure seen down the two-fold axis. The octahedra are in yellow with oxygen atoms at the four middle vertices and chlorine (green) at the two ends. Hydrogen atoms are pink. The oxygen atoms in the lone water molecules are blue.
The full structure is below. Layers alternate, offset by one half unit. The rear layer is shown in lighter colors.
Structure seen from above, showing a single layer. The hydrogen atoms attached to each octahedron are pretty much coplanar.
Below, showing two layers. Only the lower layer is shown at left.
Created 28 March 2011, Last Update 20 Sep 2011
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