Question 22.5: Sketch the structures and name the stereoisomers of Ni(NH3)4...
Sketch the structures and name the stereoisomers of Ni(NH_{3})_{4}Cl_{2}.
Collect and Organize We are given the formula and asked to name and draw the structures of the stereoisomers of a coordination compound. The Ni^{2+} complexes we have seen so far in the chapter have all been octahedral. Ammonia molecules and Cl^{-} ions are both monodentate ligands.
Analyze The formula contains no brackets, so the Cl^{-} ions are not counterions; they must be covalently bonded to the Ni ion. There are two Cl^{-} ions, so the charge on Ni must be 2+. There are a total of six ligands, which confirms that the compound is octahedral.
Solve There are two ways to orient the chloride ions: opposite each other with a Cl— Ni—Cl bond angle of 180° or on the same side of the octahedron with a Cl—Ni—Cl bond angle of 90°:
The first isomer is trans-tetraamminedichloronickel(II); the second is cis-tetraamminedichloronickel(II).
Think About It We can draw other tetraamminedichloronickel(II) structures that do not look exactly like these two structures. If we flip or rotate them, however, they will match one of the two structures shown.