(Methoxymethylidene)dimethylazanium tetraphenylborate acetonitrile monosolvate

In the cation of the title salt, C4H10NO+·C24H20B−·C2H3N, the C—N bond lengths are 1.2864 (16), 1.4651 (17) and 1.4686 (16) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.2978 (15) Å shows double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. C—H⋯π interactions are present between the methine H atom and two of the phenyl rings of the tetraphenylborate ion. The latter forms an aromatic pocket in which the cation is embedded. The iminium ion is further connected through a C—H⋯N hydrogen bond to the acetonitrile molecule. This leads to the formation of a two-dimensional supramolecular pattern along the bc plane.


D-HÁ
The phenyl rings form aromatic pockets, in which the iminium ion is embedded. The cation is further connected through a C-H···N hydrogen bond ( Fig. 2) with the acetonitrile molecule [d(H2B···N2) = 2.66 Å] (Tab. 1). This leads to the formation of a two-dimensional supramolecular pattern along the bc plane.

Experimental
The title compound was obtained by reacting equimolar amounts of N,N-dimethylformamide with dimethyl sulfate at room temperature forming methoxymethylene-N,N-dimethyliminium methyl sulfate (I). 1.00 g (5.01 mmol) of crude (I) was dissolved in 20 ml acetonitrile and 1.72 g (5.01 mmol) of sodium tetraphenylborate in 20 ml acetonitrile was added.
After stirring for one hour at room temperature, the precipitated sodium methyl sulfate was filtered off. The title compound crystallized from a saturated acetonitrile solution after several days at 273 K, forming colorless single crystals suitable for X-ray analysis.
Dimethyl sulfate is carcinogenic, mutagenic and highly poisonous. During use appropriate precautions should be taken.

Refinement
The H atom bound to C3 was located in a difference Fourier map and was refined freely [C-H = 0.94 (2) Å]. The hydrogen atoms of the methyl groups were allowed to rotate with a fixed angle around the C-N and C-O bonds to best fit the experimental electron density, with U iso (H) set to 1.5U eq (C) and d approximation, with U iso (H) set to 1.2 U eq (C).

Figure 1
The structure of the title compound with displacement ellipsoids at the 50% probability level. All carbon bonded hydrogen (except of H3) atoms were omitted for the sake of clarity.   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.