Crystal structure of (1Z)-1-(4-chlorobenzylidene)-5-(4-methoxyphenyl)-3-oxopyrazolidin-1-ium-2-ide

The planar pyrazolidine ring occurs in the betaine form with a Z conformation of the exocyclic C=N bond. In the crystal, C—H⋯O and C—H⋯π interactions result in the formation of ribbons of molecules along [10].


Chemical context
Acyclic azomethine imides are difficult to synthesize and have thus rarely been explored. However, cyclic azomethine imides of the 3-oxopyrazolidin-1-um-2-ide type are generated under mild conditions and have largely been used for the novel synthesis of heterocyclic compounds (Schantl, 2004;Padwa & Pearson, 2003) such as monocyclic and bicyclic pyrazolidinones (Zhou et al., 2013;Suarez et al., 2005) and other bicyclic heterocycles (Svete, 2006;Xu et al., 2013). Since numerous pyrazole derivatives have found use in pharmaceutical, agrochemical and other applications, for example, sildenafil or Viagra (Mulhall, 1997), lonazolac (Vinge & Bjorkman, 1986), merpirizole (Naito et al., 1969), the bicyclic pyrazolidinone LY 186826 (Indelicato & Pasini, 1988) and the developing agent in photography, phenidone, a part of our studies is focused on the synthesis of functionalized pyrazoles. For this purpose, the title compound was synthesized and the molecular and crystal structure are reported herein.

Structural Commentary
The pyrazolidine ring is planar with a maximal deviation of 0.017 (3) Å for atom C10. The 4-chlorobenzyl aromatic ring and the pyrazolidine ring are almost coplanar, making a ISSN 1600-5368 dihedral angle of 4.83 (17) , whereas the mean plane through the 4-methoxyphenyl aromatic ring is almost perpendicular [87.36 (17) ] to the pyrazolidine plane. The aromatic rings are inclined to one another at 89.23 (16) . The configuration of the exocyclic C1 N7 bond is Z. The pyrazolidine ring shows a betaine character with opposite charges located on adjacent nitrogen atoms, N1 and N2. The N1-N2 bond distance of 1.362 (3) Å agrees with the average value of 1.357 (7) Å obtained for N + -N À in pyrazolidine rings found in the Cambridge Structural Database (CSD, Version 5.35, February 2014;Allen, 2002). The intramolecular C3-H3Á Á ÁN2 interaction (Table 1 and Fig. 1) is also observed in similar compounds found in the CSD.

Supramolecular features
In the crystal packing C-HÁ Á ÁO hydrogen bonds are observed (Table 1 and Fig. 2), resulting in the formation of inversion dimers with R 2 2 (16) loops. Furthermore, the aromatic ring of the 4-chlorobenzyl substituent is involved in C-HÁ Á Á interactions (Table 1 and

Synthesis and crystallization
The starting material, ethyl p-methoxycinnamate, was isolated from Kaempferia galanga L., a traditional medicinal plant in Vietnam (Do, 2011). The reaction scheme to synthesize the title compound, (2), is given in Fig. 3.

Figure 2
Crystal packing for the title compound viewed along the a axis, with the C-HÁ Á Á and C-HÁ Á ÁO interactions drawn as dashed lines (see Table 1 for details).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.