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Ammonium ion is formed when N in $\ce{NH3}$ forms a coordinate covalent bond with a proton $\ce{(H+)}$ (or amine as shown in below picture) as a result the N gains a formal positive charge and a positive charge on the proton disappearsenter image description here

Now my question is, in a coordinate compound when $\ce{NH3}$ act as a neutral monodentate ligand i.e. N in $\ce{NH3}$ forms coordinate covalent bond with a central metal atom. Does N gains the formal positive charge? Is there is any change in the oxidation state (or charge) of a central metal atom of the coordination complex?enter image description hereenter image description here

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    $\begingroup$ Formally, yes. But don't read too much into the formal charges. They don't necessarily represent any real charge. There's no change in oxidation state; you already know that from $\ce{NH4+}$. Also, all that $\mathrm{d^2sp^3}$ "inner orbital" stuff is very outdated, and not correct. Learn it if you must, but don't propagate it. $\endgroup$
    – orthocresol
    Nov 25 '20 at 13:44
  • $\begingroup$ @orthocresol. What do you have against $\ce{d^2sp^3}$ hybridization ? Are you opposed to all hybridizations or only to this one ? $\endgroup$
    – Maurice
    Nov 25 '20 at 17:24
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Orthocresol advice of not reading too much into formal charge is sage advice.

Rephrasing your question a bit: When ammonia is coordinated to say Co as in your example, does N of the NH3 gains the formal positive charge? From the perspective and conventional thinking of inorganic chemistry, the central Co atom is a 3+ and the NH3 ligands are considered neutral. Formal charge is that, a formalism which tries to describe electron distribution in a molecule. Nature does not restrict electron distribution in whole numbers [1,2, etc.] associated with the 1- charge of electrons.

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