I understand how to find the valency of atoms in small organic compounds. For instance, for CH4, the valency of carbon is 4, while the valency of each hydrogen is 1. But for a coordination complex, for instance:

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How do I find the valency of the center metal?

And if the center metal was bound to another metal: enter image description here

How would the valency calculation change, if at all?

I need the valency of these transition metals because I wish to ultimately find the d^n configuration of the transition metal in the complex via the formula:

n = group number - valency

EDIT: If you have a different approach (apart from using valency) for finding the d^n configuration of the transition metal, feel free to suggest that instead. 

  • $\begingroup$ This formula will work for most cases of transition metals but to make it universal you should use n= ultimate s electrons + penultimate d electrons - electrovalency $\endgroup$ – Nisarg Bhavsar Apr 28 at 3:31
  • $\begingroup$ What do you mean by "valency"? The number of bonds? The oxidation state? Or something else? $\endgroup$ – matt_black Apr 28 at 12:26
  • $\begingroup$ Umm, well, valency has pretty specific meaning, it's largely forgettable beyond school, though, I guess ;) $\endgroup$ – Mithoron Apr 28 at 13:39
  • $\begingroup$ According to my lecture slides..."Valence (or valency): The valence of an atom in a covalent molecule is the number of electrons that it has used in bonding." $\endgroup$ – LamGyro Apr 28 at 15:57
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    $\begingroup$ Metal complexes are not exactly covalent, they are coordinate compounds. Generally valency isn't used for them. $\endgroup$ – S R Maiti Apr 30 at 7:39

For the first example, you are given that there are $6\, \ce{CN}$ ligands which are -1. That means that there is a total of 6- from the ligands. We also know the overall charge of the complex is -3. That means the charge of the central metal must be +3. In the second example, we can look at the charge again. Because the $\ce{CH3-}$ has a charge of -1, the molybdenum metals must have a +3 oxidation state each to counteract the -6 total charge from the $\ce{CH3-}$ groups. To do these problems, you should look at the charges of the ligands/metal(s) and the total charge of the complex and know that they have to match. After you figure out the oxidation state, you can find the $\mathrm d^n$ configuration by removing electrons from the $4\mathrm s$ subshell first and then 3$\mathrm d$. For example, For $\ce{Fe^{3+}}$, a neutral $\ce{Fe}$ atom has $6$ $3\mathrm d$ electrons. You first remove 2 electrons from the $4\mathrm s$ subshell and then a final one from the $3\mathrm d$ subshell. Finally, you will find that $\ce{Fe^{3+}}$ is $\mathrm{d}^5$. Again, this is based on the oxidation state of the metal.

  • $\begingroup$ It looks like you calculated the oxidation state for each metal. However, I was curious about the valency, not the oxidation state. $\endgroup$ – LamGyro Apr 28 at 3:28
  • $\begingroup$ Does the primary valance not indicate the oxidation state of the metal? Once you find the oxidation state, you can just use the formula you provided. n = group number - valency. Since the oxidation state of Fe in the first question was 3+, n = 8-3 = 5. We then know that it is d^5. I'm sorry if it is me misunderstanding the topic. $\endgroup$ – M.L Apr 28 at 3:55
  • $\begingroup$ Ah, I am actually not familiar with the term "primary valence." So, does that mean I can use the oxidation state in place of "valency" for the two examples? $\endgroup$ – LamGyro Apr 28 at 4:12
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    $\begingroup$ Honestly, I am not too sure. I thought you were talking about Werner's theory which I myself am not too familiar with and I literally just learned about while looking at this question. I just saw that you were trying to find d^n configuration with that formula and it works if you just use n = group number - oxidation state. $\endgroup$ – M.L Apr 28 at 4:30

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