Question

in what direction are the ions in NaCl and CsCl touching based on the unit cell? (edge, face diagonal or body diagonal)

Answer 1

NaCl has a cubic unit cell. It is face-centered cubic array of anions with an interpenetrating fcc cation lattice (or vice-versa). The cell looks the same whether you start with anions or cations on the corners.

Each ion is 6-coordinate and has a local octahedral geometry

The structure can be described as: The cesium ions from the simple cubic arrangement. Chloride ions occupy the cubic interstitial sites, i.e., each chloride ion has eight cesium ions as its nearest neighbours.