MOLECULAR-STRUCTURE AND ELECTRON-DENSITY DISTRIBUTION IN THE CRYSTALSOF 3,6-DIMETHOXY-1,2,4,5-TETRAZINE AND 3-PHENYL-1,2,4,5-TETRAZINE BASED ON X-RAY-DIFFRACTION DATA AT 120 AND 150 K - BENT BONDS IN THE 6-MEMBERED HETEROCYCLE

Characteristic features of the molecular geometry and electron density distribution in the crystals of 3,6-dimethoxy-1,2,4,5-tetrazine and 3 -phenyl-1,2,4,5-tetrazine have been studied by X-ray structural analys is and quantum-chemical (RHF and MP2) and molecular mechanics (MM3) ca lculations. An unusual shift of the maxima of the deformation electron density from the N-N bonds toward the center of the heterocycles was found, which may be interpreted as a ''bending'' of the corresponding bonds. This ''bending'' was confirmed by calculations of characteristi cs of the electron density distribution within the multipole model.