Verified answer

No, H2N3+ is correct. It is the aminodiazonium cation, H2N3+. But it certainly isn't common. I had to look up a reference. http://pubs.acs.org/doi/abs/10.1021/ja00058a031

But there is a typo in the equation you put forth. Instead of ammonia, NH3, the reactant is HN3, hydrazoic aciid. You should have written:

HN3 + HSbCl6 -> [H2N3]+ + [SbCl6]-

But keep in mind that these are not dissociated ions in aqueous solution. The resulting product is a solid "salt", and as such, the reaction looks very much like a typical Lewis acid base reaction, similar to NH3 + HCl --> NH4Cl.

The salt that is produced could be written as H2N3^+SbCl6^-, as suggested by the paper, or it could simple be written as H2N3SbCl6. The real question is whether the H is actually transferred from Sb to N to make ions, or whether the H bridges between N and Sb, or whether H is transferred to N, but the bond between N and Sb has a significant covalent character. I would bet on the last explanation.

Assuming a transfer of H, HSbCl6 would be the Bronsted-Lowry acid, and hydrazonic acid the BL base. Assuming a bond then forms between N and Sb, N would be the electron pair donor, making H2N3+ the Lewis base and SbCl6- the Lewis acid.

i think you mean NH3 + HSbCl6 -> [NH4]+ + [SbCl6]-

and yes, these are conjugate acids and bases respectively. :)