This isn't a homework question, and I've always wondered about this. My chemistry teacher told me to look up "coordinate chemistry" in a textbook, but the textbook did not have the answer. How can we predict the geometry of a coordination compound? I googled my question first, and I found that Lewis and VSEPR don't work for transition metal coordination compounds: http://answers.yahoo.com/question/index?qid=20080405102937AAOh7Gd "If your teacher thinks you can rationalize that using a Lewis structure and VSEPR principles, I'd like to see it. Pt2+ is 8 electrons, NH3 and Cl- each donate two to the bonds, that gives you 16e total around the Pt, 8 involved in bond pairs. So, that's what, AX4E4? You certainly can't use that to predict square planar, which is the observed structure. Neither can you explain why [PtCl4]2- is square planar but [NiCl4]2- is tetrahedral, even though they have the same number of valence electrons and (presumably) the same Lewis structure. Lewis and VSEPR don't work for TM compounds." I guess does that mean we can somehow predict the geometries of non-transition metal coordination complexes?