The B-F bond distance in ${\mathrm{H}}_3\mathrm{N}\to {\mathrm{BF}}_3$  is …….. than in BF₃

$\begin{array}{l}{\mathrm{H}}_3\mathrm{N}-{\mathrm{BF}}_3{\mathrm{BF}}_3\\ \downarrow \downarrow \\ {\mathrm{sp}}^3 {\mathrm{sp}}^2\end{array}$

Sp³ hybridization has less s-character when compared with sp² hydridization. 

 As s-character increases bond length decreases.