# How to determine the packing geometry of compounds with contradicting coordination number and radius-ratio values?

Determine the packing geometry of the following compounds by using the radius ratio rules. For your convenience assume a coordination number of six for both cation and anion.

Be specific in the your answer, "body-centered cubic with the anion occupying the corners of the cell [1 atom] and the cation occupying the central hole [1 atom].

Below is the table we are given, and we're are choosing between geometries of cubic, body-centered, or face-centered.

The compound I'm on is $$\ce{LiBr}$$

I did $$\frac{r^+}{r^-}=\frac{79}{182}=0.43$$ for the Radius-Ratio value.

But from here would I choose square planar because it's closer to 0.414 or do I choose octahedral because we're assuming coordination number 6? And how would I determine the locations of the cation/anion?

My best guess is cubic geometry because the cation is too large to fit tetrahedral holes and octahedral holes, with $$\ce{Li}$$ and $$\ce{Br}$$ taking occupying complementary corners.

I'm making the assumption that the coordination number 6 is used as a reference to the atomic radii.

I've currently adjusted my answer based off of other examples I could find to

FCC with OH holes occupied by $$\ce{Li^+}$$ [4 atoms] and the $$\ce{Br^-}$$ forms the FCC Lattice [4 atoms (by stoichiometry}] for a 100% occupancy rate.

But I still have an issue as to how to conceptually approach the problem.