[Firehchicken]

Hi,

How can we know whether the geometry of a complex with a coordination no. of 4 possesses a square planar or a tetrahedral geometry?

I'm really confused here. For example, I was asked to draw the d-orbital splitting diagram for [Co(Cl)₄]^2-, which I cannot do if I do not know the correct geometry 

[mjc123]

Well, you could just google it. If it comes up in an exam, where presumably you can't google it, that means you're just expected to know. There's a certain amount you just have to learn, and shapes of common transition metal complexes would come into that category.
But there are some rules that can help you. Did you read my last post in your other TM thread?
(You seem to have a habit of running away and not responding - then asking a very similar question again in a new thread. I hope I'm not scaring you off! It would be courteous to respond - if my post helped you to solve the problem, it would be nice to get a "thank you"; if not, it would help us both if you say what you still don't understand.)

[jestearns]

Think valence electrons.