Orphenadrinium dihydrogen citrate

In the title salt, C18H24NO+·C6H7O7 −, the dihedral angle between the benzene rings in the cation is 74.2 (5)°. In the crystal, anion–anion O—H⋯O hydrogen bonds and weak O—H⋯O interactions form infinite chains along [100]. Between these chains, cation–anion N—H—O hydrogen bonds are observed, forming an alternate pattern of cation and anion layers and leading to a two-dimensional network parallel to (100).

In the title salt, C 18 H 24 NO + ÁC 6 H 7 O 7 À , the dihedral angle between the benzene rings in the cation is 74.2 (5) . In the crystal, anion-anion O-HÁ Á ÁO hydrogen bonds and weak O-HÁ Á ÁO interactions form infinite chains along [100]. Between these chains, cation-anion N-H-O hydrogen bonds are observed, forming an alternate pattern of cation and anion layers and leading to a two-dimensional network parallel to (100).  Table 1 Hydrogen-bond geometry (Å , ). anticholinergic drug of the ethanolamine antihistamine class with prominent CNS and peripheral actions used to treat painful muscle spasm and other symptoms and conditions as well as some aspects of Parkinson's disease. It is closely related to diphenhydramine and therefore related to other drugs used for Parkinson's disease like benztropine and trihexyphenidyl and is also structurally related to nefopam, a centrally acting yet non-opioid analgesic. Clinical and pharmacological review of the efficacy of orphenadrine and its combination with paracetamol has been described (Hunskaar & Donnel, 1991). Orphenadrine citrate is a skeletal muscle relaxant. It acts in the central nervous system to produce its muscle relaxant effects. The orphenadrine salt used for Parkinsonism is the hydrochloride, whereas the muscle relaxant tablet is the citrate. The solid-state structure of orphenadrine hydrochloride and conformational comparisons with diphenhydramine hydrochloride and nefopam hydrochloride is reported (Glaser et al., 1992). The crystal structure of orphenadrinium picrate picric acid (Fun et al., 2010) and orphenadrinium picrate (Jasinski et al., 2011) is recently reported. In view of the importance of orphenadrine, this paper reports the crystal structure of the title salt, (I), C 18 H 24 NO + . C 6 H 7 O 7 -.

Related literature
In the title salt, C 18 H 24 NO + . C 6 H 7 O 7 -, one cation-anion pair crystallizes in the asymmetric unit (Fig. 1). The cation contains a positively charged N atom with quaternary character. The anion consists of a dihydrogen citrate counterion.
The dihedral angle between the two benzene rings in the cation is 74.2 (5)°. Bond lengths are in normal ranges (Allen et al., 1987). In the crystal anion-anion O-H···O hydrogen bonds and weak O-H···O intermolecular interactions form infinite chains along [100] (Table 1). In between these chains cation-anion N-H-O hydrogen bonds are observed forming an alternate pattern of cation and anion layers forming a two-dimensional network providing additional crystal stability ( Fig. 2).

Experimental
The title compound was obtained as a gift sample from R. L. Fine Chem, Bengaluru. The compound was recrystallized from methanol by slow evaporation (m. p.: 410 K).

Refinement
All of the H atoms were placed in their calculated positions and then refined using the riding model with Atom-H lengths of 0.93Å (CH), 0.97Å (CH 2 ), 0.96Å (CH 3 ) 0.82Å (OH) or 0.91Å (NH). Isotropic displacement parameters for these atoms were set to 1.18-1.21 (CH, CH 2 , NH), 1.50 (CH 3 ) or 1.48-1.50 (OH) times U eq of the parent atom. The highest peak (0.67 e/A 3 ) is located 0.87 Å from H4.     (7) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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.