MOLECULAR AND CRYSTAL ENGINEERING STUDIES OF 2 2,4-DINITROALKOXYSTILBENES - AN ENDEAVOR TO GENERATE EFFICIENT SHG CRYSTAL

The crystal structure analyses of 2,4-dinitro-3',4'-methylenedioxystil bene and 2,4-dinitro-3',4',5'-trimethoxystilbene have been carried out . Even though both the structures consist of molecular layers, the for mer crystallizes in a centrosymmetric space group, and the latter adop ts a noncentrosymmetric structure. Rationale for the formation of thes e layers and their subsequent difference in stacking is presented in t erms of the C-H ... O interactions and nonplanarity of the molecular s tructure. The semiempirical calculations indicated that the hyperpolar izability varies a little (<3%) for a 20-degrees rotation in the stilb ene backbone. Due to a nonoptimal alignment of dipole in crystal, the dinitrotrimethoxystilbene is feebly SHG active in the powder state (0. 2 X urea). Packing energy calculations and analyses of the X-ray powde r patterns suggested the possible existence of another form of the din itromethylenedioxystilbene. Crystal packing analyses of methylenedioxy , trimethoxy, and nitro groups reveal the importance of orientational effects and molecular nonplanarity in the generation of noncentrosymme tric crystal packing.