The reaction of B10H12(SMe2)2 with HN3 yields arachno-B10H12(N3)(NH2) (I), a product with a m-NH2 group. I can be hydrolyzed to give the known arachno-B9H13(NH3). nido-NB9H11(N3) is formed from I by a deprotonation/protonation sequence. The azaborane nido-NB10H13 is a product of the thermolysis of I. The structure of I was elucidated by an x-ray structure anal.