La in solid LaBr₃ has a tricapped trigonal-prismatic coordination. What is the coordination number of Br? Is it possible that the tricapped trigonal prisms share only corners, or would you expect sharing of edges and/or faces? Check the result by viewing the structure and constructing polyhedra around La (P6₃/m, a = 7.971, c = 4.522 Å. La in 2c at ⅓ ⅔ ¼, Br in 6h at 0.3849 0.2988 ¼).