Ml. Glowka et al., Crystal and molecular structures of 1,1-bis(methylthio)-4-(2-pyridyl)-2,3,5-triaza-1,3-pentadiene and its 5-phenyl derivative, POL J CHEM, 73(5), 1999, pp. 845-851
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.