Tetramethylammonium (Z)-N′-cyanocarbamimidate

The structure of the tetramethylammonium salt of cyanourea is reported.


Structure description
Cyanourea and its salts have been the subject of much interest including the use of its derivatives in the study of solid state reaction mechanisms (Lotsch & Schnick, 2004), as substituents in manipulating the conformation of calix [4]arenes (Ling et al., 2014), in the synthesis of amide-acid chloride adducts in organic synthesis (Harris, 1981), and in modulating the magnetic properties of Mn 6 clusters (Yang et al., 2009). In spite of this interest there has been very little structural characterization of this moiety and only structures of its ammonium (Lotsch & Schnick, 2004), silver (Britton, 1987), and potassium salts (Magomedova & Zvonkova, 1974) have been reported.
In the title compound, [C 4 H 12 N] + [C 2 H 2 N 3 O] À , 1, the tetramethyl ammonium salt of cyanourea is reported and shown in Fig. 1. The N-C and O-C bond distances in the cyano and keto groups [1.1641 (18) and 1.2550 (16) Å ,respective] are in the normal range for such a moieties and similar to the values found for the silver salt [1.149 (6) and data reports 1.248 (5) Å , respectively]. However, the bonds about C5 and N3 are much shorter than would be expected for single bonds ( Table 1) and indicate that there is considerable electron delocalization in the anion, as was also found in the silver salt. In 1, the NH 2 group is coplanar with the central N 2 CO core [dihedral angle between NH 2 and N 2 CO planes of only 0.54 (8) ] in contrast with the nitrile group where the dihedral angle between the N-C-N and N 2 CO planes is 36.5 (3) . These values are different to those found in the silver salt where the corresponding angles are 23 (6) and 4.5 (3) .
The packing of the cations and anions in the unit cell involves N-HÁ Á ÁO hydrogen bonds (Table 2) between anions characterized by an R 2 2 (8) motif as well as N-HÁ Á ÁO hydrogen bonds between anions and C-HÁ Á ÁO interactions between both cations and anions forming an R 3 3 (14) pattern as shown in Fig. 2.

Figure 2
Diagram showing the packing of the cations and anions in the unit cell, which involves N-HÁ Á ÁO hydrogen bonds between anions characterized by an R 2 2 (8) motif as well as N-HÁ Á ÁO hydrogen bonds between anions and C-HÁ Á ÁO interactions between both cations and anions forming an R 3 3 (14) pattern (all interactions shown with dashed lines).

Figure 1
Diagram showing the [C 4 H 12 N] + cation and [C 2 H 2 N 3 O 3 ] À anion linked by a C-HÁ Á ÁO interaction (shown as a dashed line). Atomic displacement parameters are drawn at the 30% probability level.

Synthesis and crystallization
An ion-exchange column packed with Dowex HCR-W2 resin was regenerated with 3M HCl and washed with water. A solution of 5.00 g of NaN(CN) 2 was run through the column and the product was neutralized with Me 4 NOH until alkaline. The solution was roto-vapped to dryness, recrystallized from EtOH, washed with MeOH and recrystallized from EtOH again, and pumped to dryness to afford about 1 g of product.
Apparently the dicyanamide was partially hydrolyzed to form cyanourea when in free acid form.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The structure was refined as a twocomponent twin with a fractional contribution of 0.0409 (11) for the minor domain. 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. Refined as a 2-component twin. The structure was solved using SHELXT (Sheldrick, 2015a) and refined with SHELXL2018 (Sheldrick, 2015b). The locations of all hydrogen atoms for the major component were located in difference Fourier maps and refined in idealized position using a riding model with atomic displacement parameters of U iso (H) = 1.2U eq (C, N) [1.5U eq (C) for CH 3 ], with N-H distance of 0.88 Å and C-H distances ranging from 0.95 to 0.99 Å, respectively.