Synthesis and structure of a novel mesomeric betaine 6,7-dimethyl-2H-pyrazolo[4,3-e]tetrazolo[4,5-b][1,2,4]triazine

The synthesis and structural characterization by H-1 NMR, HRMS, elemental analysis and X-ray crystallography of a novel mesomeric betaine, 6,7-dimethyl-2H-pyrazolo[4,3-e]tetrazolo[4,5-b][1,2,4]triazine 8a are described. The compound 8a crystallizes in the monoclinic system in the space group P2(t)/n with a=11.766(2), b=5.8097(12), c=12.389(3)angstrom, beta=107.14(3)degrees, V=809.2(3)angstrom(3), Z=4, D-calc=1.561 gcm(-3), lambda(Cu K alpha)=1.54178 angstrom, mu=0.953mm(-1) and final R=0.0378 for 1526 reflections. The molecule as a whole has an almost planar conformation and the bond lengths and angles have the values characteristic for pi-electron system. The molecular packing in the crystal is influenced by the van der Waals forces and presence of weak pi-pi interactions. The electronic properties (net charge and MEP distributions and dipole moment) of the molecule 8a are calculated using AMI approximation. Twelve dipolar canonical forms for molecule 8a are presented and their contribution in mesomeric betaine structure of 8a is discussed (molecular mechanics calculations). (c) 2006 Elsevier B.V. All rights reserved.