I know that coordination numbers of cations and anions in ionic lattices must correlate with the ratios of ions in the empirical formula, but are there exceptions to this rule?
For example, I am having issues with a certain problem: Picture a crystal lattice with the anions making up a body-centered cubic cell, with the cations in the middles of the faces of the cell. Consequently, the number of anions in the unit cell is 2, and the number of cations in the unit cell is 3. However, I keep getting that the coordination number of the anion is 12 and that of the cation is 6, which is not in keeping with the empirical formula implied by the previous sentence.
Would really appreciate some help