5,6,7,8-Tetrafluoro-3 lambda(4)delta(2),1,2,4-benzothiaselenadiazine (1) is prepared by the intramolecular nucleophilic cyclization of C6F5SeN=S=NSiMe3 (2) mediated by CsF. According to an X-ray diffraction analysis, the heterocycle of 1 is bent along the Se(1)center dot center dot center dot N(4) line by 6.0(2)degrees in the crystal. Despite the obvious similarities between 1 and its 1,3-dithia analogue (7) with respect to molecular composition and shape, the crystal packing of 1 is substantially different from that of 7. An interesting consequence of this is the inclusion of atmospheric N-2 in the crystal lattice of the selenium derivative 1. The molecular structure and bonding of 1 have been investigated using quantum-chemical calculations at the DFT/B3LYP/6-311+G* level of theory, and the results have been compared to those of 5,6,7,8-tetrafluoro-1,3 lambda(4)delta(2),2,4-benzodithiadiazine (7) and their hydrocarbon analogues (5 and 8).