Crystal structure of 4-[[(1E)-(2-hydroxynaphthyl)methylidene]amino]-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one.

bonds [either N–H···O (keto-amine tautomer) or N···H–O (phenol-imine tautomer)] can exist. It is claimed that the hydrogen-bond type depends neither on the stereochemistry of the molecule nor on the sort of substituent bonded to the N imino atom, but on the kind of aldehyde used.1 In the solid state, it is also claimed that only an intramolecular N–H···O type hydrogen bond is present in naphthaldimines regardless of the kind of N-substituents, aryl or alkyl.2 However, our crystallographic studies have shown an intramolecular (N···H–O (phenol-imine tautomer) hydrogen bond, which is in contrast to observations reported in the literature.2,3 The title ligand was prepared from a mixture of 2hydroxy-1-naphthaldehyde (0.60 g, 3.5 mmol) and 4aminophenazone (4-AAP) (0.71 g, 3.5 mmol) in boiling methanol (100 ml). After the precipitate was filtered, the residue was dissolved in CHCl3–EtOH (3:1) and set aside for crystallization (yield 0.80 g, 64%; m.p. 491 K). 4-AAP and its derivatives are very important compounds in pharmacology and biochemistry. They are especially used as anti-inflammatory drugs.4 The results of X-ray structure determinations are given in Tables 1 – 3. The hydrogen atoms were located by a difference Fouirer synthesis and a geometrical calculation, with the parameters of 4 hydrogen atoms (H1, H71, H111, H181) (out of 19) being refined. The title molecule (Fig. 2) has a short intramolecular N···H–O hydrogen bond [O1–H1 0.953(3), H1···N1 1.497(3), N1···O1 215 ANALYTICAL SCIENCES FEBRUARY 2002, VOL. 18 2002 © The Japan Society for Analytical Chemistry