Crystal and molecular structures of 1,1-bis(methylthio)-4-(2-pyridyl)-2,3,5-triaza-1,3-pentadiene and its 5-phenyl derivative

Structures of the two dimethylthiomethylene-2-pyridinecarboxamide hydrazone s have been examined spectroscopically and by X-ray diffraction to establis h the dominant tautomeric form and conformation. The two crystal structures are very similar with approximately planar conformation and intramolecular hydrogen bond between 4-imine group as hydrogen donor and pyridyl N atom a s an acceptor. Several significant differences found may be easily explaine d by phenyl substitution in one of the compounds. The benzene ring in compo und 2 is twisted by about 40 degrees in relation to the mean molecular plan e due to packing forces. An interesting feature of the structures is the de viation of the pyridyl ring by 11-14 degrees from the mean 2,3,5-triaza-1,3 -pentadiene plane in the two structures, despite the intramolecular hydroge n bond spanning the two fragments. It agrees with the elongation of C(4)-py ridine bond to 1.488 Angstrom, which corresponds with the lack of conjugati on between pi electrons of the pyridine ring and a lone pair at adjacent N( 4) atom.