STRUCTURAL STUDIES OF 3 ISOMERIC FORMS OF HETEROCYCLIC N(4)-SUBSTITUTED THIOSEMICARBAZONES AND 2 NICKEL(II) COMPLEXES

Three structural forms have been isolated among four 2-formyl- and 2-a cetylpyridine N(4)-substituted thiosemicarbazones reported. 2-Formylpy ridine N(4)-methylthiosemicarbazone and 2-acetylpyridine N(4)-ethylthi osemicarbazone both exist as nonhydrogen bonding E isomers. 2-Formylpy ridine 3-azabicyclo[3.2.2]nonylthiosemicarbazone crystallizes as a hyd rogen bonding Z isomer. The yellow 2-acetylpyridine 3-hexamethyleneimi nylthiosemicarbazone crystallized with a bifurcated hydrogen bonding a rrangement in which the N(3) hydrogen is formally positioned at N(2), making it tautomeric to the other two forms. Structures of four-coordi nate nickel(II) complexes containing the monoanions of 2-formylpyridin e 3-azabicyclo[3.2.2]nonylthiosemicarbazone and acetylpyrazine 3-hexam ethyleneiminylthiosemicarbazone are included.