Structural studies of 3-tert-butyl-8-(methylchalcogenyl)pyrazolo[5,1-c][1,2,4]triazin-4(1H)-ones

Crystal structures of novel 3-tert-butyl-8-(methylchalcogenyl)pyrazolo[5,1-c][1,2,4]triazin-4(1H)-ones, C10H14N4OE (E = S, 3; Se, 4; Te, 5), have been determined. Compound 3 crystalizes in the monoclinic crystal system (P21/c), whereas 4 provides two polymorph modifications, 4a (orthorhombic, Pbca) and 4b (tetragonal, I41/a, merohedral twin), depending on solvent media. Crystal structure of 5 (tetragonal, I41/a) is isomorphous with 4b. The studied structures of pyrazolo[5,1-c][1,2,4]triazin-4(1H)-ones exhibit a planar heterocyclic C5N4O core possessing a conjugated π-electron system, which is partly involved in the conjugation with the chalcogen atom. In general, geometric parameters found by X-ray method and ab initio calculated by density functional theory (DFT) for a single molecule (method PBE1PBE/Def2TZV, gas phase) are in good agreement. The structures form 1D infinite chains in the crystalline lattice via intermolecular NH∙∙∙O/N hydrogen bonding and demonstrate short E···E (3, 4b, 5) and E···C/N (all compounds) interactions among molecules of the neighboring chains. Such non-valence interactions do not perturb much the geometries of 3, 4b, and 5 but move the Se atom out of the C5N4O plane in 4a, compared with geometries calculated by DFT method. Photochemical studies have revealed that UV irradiation induces decomposition of telluride 5, accompanied with the Te-C8 bond cleavage, while sulfide 3 and selenide 4 remain inert under analogous conditions.