Crystal structure of (Z)-N-benzylidene-1-phenylmethanamine oxide hydrogen peroxide monosolvate

The title structure consists of a (Z)-N-benzylidene-1-phenylmethanamine oxide and a hydrogen peroxide molecule linked through both O—H groups into a one-dimensional chain structure.


Chemical context
Peroxosolvates are solid adducts that contain hydrogen peroxide molecules of crystallization in the same manner as the water in crystalline hydrates. Today, some of these are widely used as environmentally friendly bleaching compounds (Jakob et al., 2012) and oxidizing agents in organic synthesis (Ahn et al., 2015). Hydrogen bonding in peroxosolvates is of particular interest since it may be used for modelling of hydrogen peroxide behaviour in various significant biochemical processes (Kapustin et al., 2014).
It is known that nitrones R 1 -CH N(O)-R 2 [R 1 , R 2 = aryl (Ar) or alkyl (Alk)] are readily available by oxidation of secondary amines using hydrogen peroxide (Goti et al., 2005). We supposed that the combination of oxidizing and cocrystallizing properties of hydrogen peroxide might afford an opportunity to obtain nitrone peroxosolvates in one step. We prepared the title 1:1 adduct of (Z)-N-benzylidene-1-phenylmethanamine oxide with hydrogen peroxide and the structure is reported herein.

Structural commentary
In the structure of the title adduct ( Fig. 1), all bond lengths and angles in the organic coformer exhibit normal values for nitrone derivatives (Cambridge Structural Database, Version 5.38, May 2017; Groom et al., 2016). The nitrone fragment Ph-CH N(O)-C is planar to within 0.128 (3) Å . It is almost perpendicular to the benzyl substituent C11-C17, with an O3-N1-C11-C12 torsion angle of 72.7 (4) , and forms a dihedral angle between the two aryl rings of 81.9 (2) . This is the same conformation as was previously observed in the structure of the pure coformer (Herrera et al., 2001). The organic molecule forms two hydrogen bonds, involving the negatively charged oxide atom O3, with adjacent peroxide molecules and the conformation is stabilized by an aromatic C27-HÁ Á ÁO3 hydrogen bond (Table 1). As expected, the N1-O3Á Á ÁO(peroxo) angles are close to trigonal [117.9 (2) and 126.2 (2) ].
In the peroxide molecule, the O-O distance is 1.467 (4) Å . This value is close to those previously observed in the accurately determined structures of crystalline hydrogen peroxide [1.461 (3) Å ; Savariault et al., 1980] and urea perhydrate [1.4573 (8) Å ; Fritchie & McMullan, 1981]. Partial substitutional disorder of hydrogen peroxide by water molecules (Pedersen, 1972) was not observed in the present structure since no residual peaks with an intensity of 0.14 e Å À3 were seen in the hydrogen peroxide molecule region (Churakov et al., 2005). The H 2 O 2 molecule lies on a general position and presents a skew geometry, with the H-O-O-H torsion angle equal to 88 (4) , and forms just two donor hydrogen bonds. It should be noted that the maximum possible number of hydrogen bonds formed by H 2 O 2 is six (two donor and four acceptor; Chernyshov et al., 2017).

Supramolecular features
In the title crystal, the organic and peroxide molecules are linked into hydrogen-bonded chains extending along the b axis through charge-supported moderate HOOHÁ Á Á À O-N hydrogen bonds, with OÁ Á ÁO separations of 2.707 (5) and 2.681 (5) Å (Table 1 and Fig. 2). Similar chains formed by N-oxide and H 2 O 2 molecules were previously observed in the structure of risperidone N-oxide hydrogen peroxide methanol solvate (Ravikumar et al., 2005). In the present one-dimensional structure, minor weak non-aromatic C-HÁ Á ÁO(peroxide) hydrogen-bonding interactions are also present.

Database survey
The Cambridge Structural Database (Groom et al., 2016) contains data for nine peroxosolvates of N-and P-oxides with one or two R 3 X + ! O À functional groups (X = N, P; R = Alk, Ar). It is of interest that all of these were obtained by oxidation of the corresponding amines (phosphines) using hydrogen peroxide, followed by immediate crystallization from the reaction mixtures. Analysis of the crystal packing for these compounds reveals three main supramolecular motifs  Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x; y þ 1; z; (ii) x; Ày þ 3 2 ; z À 1 2 .

Figure 1
The asymmetric unit in the title structure. Displacement ellipsoids are shown at the 50% probability level and the hydrogen bond is drawn as a dashed line.

Figure 2
Hydrogen-bonded chains extending along the b axis. H atoms on C atoms have been omitted for clarity. Hydrogen bonds are drawn as dashed lines.

Synthesis and crystallization
Needle-shaped crystals of the title compound crystallized spontaneously from a saturated solution of dibenzylamine in 50% hydrogen peroxide after holding for 3 d at room temperature. Caution! Handling procedures for concentrated hydrogen peroxide (danger of explosion) are described in detail by Wolanov et al. (2010).

Figure 3
Hydrogen-bonded motifs in the structures of N-and P-oxides.

Computing details
Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008). Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.034 (6) 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 > 2sigma(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.