(Butoxymethylidene)dimethylazanium tetraphenylborate acetonitrile monosolvate

In the title solvated salt, C7H16NO+·C24H20B−·C2H3N, the C—N bond lengths in the cation are 1.2831 (19), 1.467 (2) and 1.465 (2) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.2950 (18) Å shows a double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. The two C atoms of the n-butyl group are disordered over the two sites, with refined occupancy ratios of 0.890 (5):0.110 (5) and 0.888 (4):0.112 (4). In the crystal, C—H⋯π interactions occur between the methine H atom, H atoms of the –N(CH3)2 and –CH2 groups of the cation, and two of the phenyl rings of the tetraphenylborate anion. The latter interaction forms an aromatic pocket in which the cation is embedded. Thus, a two-dimensional pattern is created in the ac plane.

In the title solvated salt, C 7 H 16 NO + ÁC 24 H 20 B À ÁC 2 H 3 N, the C-N bond lengths in the cation are 1.2831 (19), 1.467 (2) and 1.465 (2) Å , indicating double-and single-bond character, respectively. The C-O bond length of 1.2950 (18) Å shows a double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. The two C atoms of the n-butyl group are disordered over the two sites, with refined occupancy ratios of 0.890 (5):0.110 (5) and 0.888 (4):0.112 (4). In the crystal, C-HÁ Á Á interactions occur between the methine H atom, H atoms of the -N(CH 3 ) 2 and -CH 2 groups of the cation, and two of the phenyl rings of the tetraphenylborate anion. The latter interaction forms an aromatic pocket in which the cation is embedded. Thus, a twodimensional pattern is created in the ac plane.
Cg1 and Cg2 are the centroids of the C14-C19 and C8-C13 rings, respectively. According to the structure analysis, the C1-N1 bond length is 1.465 (2)  positive charge is completely delocalized in the plane of the atoms N1, C3 and O1. The n-butyl group is disordered over the two sites with refined occupancies of 0.888 (5) and 0.112 (5). The bond lengths and angles in the tetraphenylborate anion are in good agreement with the data from the crystal structure analysis of the alkali metal tetraphenylborates (Behrens et al., 2012). A strong C-H···π interaction between the hydrogen atom H3 of the cation and one phenyl ring (Cg1) of the tetraphenylborate anion is observed (Fig. 2). Slightly weaker C-H···π interactions between the hydrogen atoms of -N(CH 3 ) 2 and -CH 2 groups and a second phenyl ring (Cg2) are also present (Fig. 2, Table 1). The hydrogen centroid distances are 2.55, 2.62, 2.65 and 2.78 Å (Tab. 1), respectively. The phenyl rings form aromatic pockets, in which the iminium ion is embedded. This leads to the formation of a two-dimensional supramolecular pattern in the ac plane. In contrast to the crystal structure of (methoxymethylidene)dimethylazanium tetraphenylborate acetonitrile monosolvate (Tiritiris et al., 2014), the acetonitrile molecule is hardly involved in a C-H···N hydrogen bond system.

Experimental
The title compound was obtained by reacting of equimolar amounts of N,N-dimethylformamide with dimethyl sulfate at room temperature forming (methoxymethylidene)dimethylazanium methyl sulfate (I). One mol of (I) was heated with 2.2 mol n-butanol for eight hours at 313 K. The methanol formed was distilled off and (butoxymethylidene)dimethylazanium butyl sulfate (II) was obtained in nearly quantitative yield. 1.00 g (3.66 mmol) of crude (II) was dissolved in 20 ml acetonitrile and 1.25 g (3.66 mmol) of sodium tetraphenylborate in 20 ml acetonitrile was added. After stirring for one hour at room temperature, the precipitated sodium butyl sulfate was filtered off. The title compound crystallized from a saturated acetonitrile solution after several days at 273 K, forming colourless single crystals suitable for X-ray analysis.
Dimethyl sulfate is carcinogenic, mutagenic and highly poisonous. During the use appropriate precautions must be taken.

Refinement
The H atom bound to C3 was located in a difference Fourier map and was refined freely [C-H = 0.95 (2)  best fit the experimental electron density, with U iso (H) set to 1.5U eq (C) and d(C-H) = 0.98 Å. The remaining H atoms were placed in calculated positions with d(C-H) = 0.99 Å (H atoms in CH 2 groups) and (C-H) = 0.95 Å (H atoms in aromatic rings). They were included in the refinement in the riding model approximation, with U(H) set to 1.2 U eq (C).
Atoms C5 and C6 of the n-butyl group are disordered over two sites (C5A, C6A and C5B,C6B) with refined occupancies of 0.888 (5) and 0.112 (5). A free refinement of the anisotropic displacement parameters of the atoms C5B and C6B (minor moiety) was not possible, so an ISOR = 0.001 instruction for C6B was established, which solves this problem. Finally, the atoms C5B and C6B were restrained to have similar anisotropic displacement parameters. Nevertheless, it was not possible to prevent the detection of an A-alert in the checkcif utility. There is a large U eq (max)/U eq (min) ratio of the hydrogen atoms, caused by the large U eq of the terminal methyl group hydrogen atoms and the small U eq of the hydrogen atoms attached to the atoms C5B and C6B in the disordered n-butyl moiety.

Figure 1
The structure of the title compound with displacement ellipsoids at the 50% probability level. All carbon bonded hydrogen atoms (except of H3) were omitted for the sake of clarity. Only the major orientation [pp = 0.888 (5)

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.