The crystal and molecular structures of nicotinhydroxamic acid acid its com
plex with Mo(VI) were studied by X-ray diffraction. It is shown that a mole
cule of nicotinhydroxamic acid has the keto tautometric form, while, in the
complex structure, it is in the enol form. The molecules of nicotinhydroxa
mic acid are connected into chains via hydrogen bonds; crystallization wate
r molecules and the potassium cations promote the formation of a complex la
yer structure.