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How can I determine if a coordination compound has a tetrahedral or square planar geometry without any experimental data (such as magnetic spin) by just looking at its formula?

For example, what is the geometry of the following complexes:

  • $\ce{[CoCl4]^2-}$
  • $\ce{[Ni(CN)4]^2-}$
  • $\ce{[CuCl4]^2-}$

Do they have a Jahn-Teller distortion?

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closed as too broad by Mithoron, Mathew Mahindaratne, Todd Minehardt, F'x, Tyberius Jul 5 at 0:51

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Your question is like asking "how do I tell whether an object weighs more than a kilogram without measuring its mass". For some objects, it's obvious: a feather is definitely under 1 kg, an elephant definitely over. For some other things, your eyes aren't good enough and the only way to know is to put it on a scale. A more nuanced question, and probably better, would be to ask what factors tend to favour tetrahedral geometries vs square planar geometries. Some of them are touched upon here: chemistry.stackexchange.com/q/40880/16683 $\endgroup$ – orthocresol Jun 27 at 13:51
  • $\begingroup$ Thank you for your time. I know that question is a bit odd but this is a question from my last inorganic chemistry exam. Well, let me write that question exactly, Wich one of those ligands you can observe Jahn-Teller Distortion? and why? [CoCl4]2− [Ni(CN)4]2− [CuCl4]2− $\endgroup$ – İsmail Burak AYDIN Jun 27 at 15:59
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    $\begingroup$ As speculation: if it was an examination question, perhaps especially an oral one, see it as a check about «how would you answer this later in professional life by yourself»: display both the pathway (your reasoning «because of chlorine ligands ...») as well as your answer («so x and y were square panar, z however tetrahedral») plus a probe («which could be experimentally confirmed by method A»). For your comment, put forward your new arguments -- even if they do not lead yet to an answer, it will 1) show us where to help you and 2) show you to yourself what you already understood. $\endgroup$ – Buttonwood Jun 28 at 21:34
  • $\begingroup$ For example [Ni(CN)4]2− I've drawn energy diagram for that compound both tetrahedral and square planar, put electrons with respect to strong field ligand and as you did say and I've made consumptions about Jahn-Teller distortion for both geometries. What i couldn't get is, if this the right way to do it? Note that i don't have any extra data $\endgroup$ – İsmail Burak AYDIN Jun 29 at 13:29