Consider a hypothetical compound $\ce{H3NF2}$. What will be its Lewis dot structure? I'm stuck, since Nitrogen cannot exhibit pentavalence, or at least its not stable (unlike phosphorous in $\ce{H3PF2}$). Will the compound be ionic?

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    $\begingroup$ You seem to be acting on the premise that any random text string represents a compound. This is not true. $\endgroup$ – Ivan Neretin Nov 8 '20 at 13:34
  • $\begingroup$ Why discuss the structure of non-existent compounds ? $\endgroup$ – Maurice Nov 8 '20 at 17:17

In principle, such a compound is possible by allowing an ionic structure, to wit $\ce{[NH3F+][F-]}$ where the cation has the usual tetrahedral structure for an ammonium ion, with nitrogen at the center and three hydrogen and one fluorine atom attached to it.

Whether this compound exists is another matter. We may expect such a B-L acidic cation to protonate the fairly strongly basic fluoride ion so that our proposed $\ce{[NH3F+][F-]}$ would break up into $\ce{NH2F + HF}$.

However, the cation $\ce{NH3F+}$ does exist with more inert counterions such as trifluoromethylsulfonate (triflate), $\ce{CF3SO3^-}$. Spectroscopic data are reported with the triflate salt as well as a couple salts involving more highly fluorinated ions in the table below from Olah et al. [1].

Table 2.1 Multinuclear NMR data on fluoroammonium ions and comparison with NH4+


  1. G. A. Olah, K. K. Laali, Q. Wang, G. K. Surya Prakash, Onium Ions (New York: John Wiley and Sons, 1968), p. 15.

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