During combination of species BH3 and NH3 , N atom of NH3 is donor and B atom of BF is acceptor. The hybrid state of B in BF3 is sp² and that of N in NH3 is sp³.
In the compound F3B+ -NH3- both N and B atoms are surrounded by four bond pairs. Thus, the hyrid state of both is sp³. Hence during the reaction the hybrid state of B changes from sp² to sp³ but that of N remains the same.
