[elt2112]

Explain why lanthanum is 11 coordinate in LaF₃, whilst lutetium is 9 coordinate in LuF₃, but 6 coordinate in LuCl₃.

So I'm guessing the fact that lutetium 3+ has a significantly smaller ionic radius would account for the fact it has a smaller coordination number. But what reason is there for the difference between LuF₃ and LuCl₃? Would it be because chlorine is larger than fluorine?

[mjc123]

Yes