Using a miniature zone melting device with focused IR light it was possible to grow crystals of bis(dimethylamino)methylborane (I) and bis(monomethylamino)methylborane (II) at temps. of 182 K and 177 K, resp. The crystal structure and the X-X difference electron d. have been detd. at temps. of 120 K (I) and 115 K (II). It is shown that the variation of torsion angles at small angles has more influence on bond lengths than the same or a greater variation at large angles and that it is necessary to pay more attention to the torsion angles (C-B-N-C) rather than to the interplanar angles (plane N,B,N-plane N,C,C).