N-[Amino(imino)methyl]uronium tetrafluoroborate

In the title compound, C2H7N4O+·BF4 −, intermolecular N—H⋯O hydrogen bonds connect the cations into chains parallel to the c axis, with graph-set motif C(4). These chains are in turn connected into a three-dimensional network by intermolecular N—H⋯F hydrogen bonds. The B—F distances distances in the anion are not equal.

In the title compound, C 2 H 7 N 4 O + ÁBF 4 À , intermolecular N-HÁ Á ÁO hydrogen bonds connect the cations into chains parallel to the c axis, with graph-set motif C(4). These chains are in turn connected into a three-dimensional network by intermolecular N-HÁ Á ÁF hydrogen bonds. The B-F distances distances in the anion are not equal.
This was also the case for the consideration of preparation of the title structure with a tetrahedral [BF 4 ]anion which would enhance a chance for the formation of a stronger N-H···F hydrogen bond even in presence of the competing carbonyl group in the 2-carbamoylguanidinium cation.
The symmetry equivalent N1-H1n2···O1 hydrogen bonds form chains extended along the unit-cell axis c (Fig. 3). The pertinent graph set motif is C(4) (Etter et al., 1990). It is of interest that the secondary amine forms stronger N-H···O hydrogen bonds than the primary amines also in tris (2- The χ 2 index through the cation's non-hydrogen atoms of the title structure equals to 4671.953. This is less than in the most probably less stable polymorph of bis(2-carbamoylguanidinium) fluorophosphonate dihydrate (Fábry et al., 2012b) with the χ 2 index of 19477.0, and in 2-carbamoylguanidinium hydrogen phosphite with the χ 2 index of 6515.041 (Fridrichová, Němec, Císařová & Němec, 2010;Fábry et al., 2012c). On the other hand, it is considerably more than e. g.
the corresponding values regarding the two independent molecules in the presumably more stable polymorph of bis(2- The volume of the solution after neutralization was about 30 ml. Tiny crystals floating in the solution appeared in a few days. However, they disappeared in the course of time while being replaced by a white powder. The crystal used for the structure analysis was grown from a drop of the mother liquor on a glass. (The glass was not seemingly affected by the solution.) The powder is a different compound or phase because another grown crystal dissolved in a drop that contained the particles of the powder. The obtained crystals were colourless plates with dimensions of several tenths of mm.
The calorimetric experiments were performed on differential scanning calorimeters Perkin  and PerkinElmer Pyris Diamond DSC (298-493 K). Pyris Software (Version 4.02, PerkinElmer Instruments, 2001) was used for control and evaluation. The sample (m = 11 mg) was hermetically closed in an aluminium 30µl pan, the scanning rate was 10 K/min. The DSC sample holder was purged by helium (DSC 7) or nitrogen (Pyris Diamond). Below room temperature a tiny peak is observed at 267K on heating, probably because of a residue of water. Above room temperature, a distinct exothermic peak with an endothermic onset was found at about 463K on the first heating. This exothermic reaction obviously changed the composition of the sample because two peaks that had not been observed on the very first heating were observed in subsequent runs both on heating (at 422K and 477K) and on cooling (at 409K and 462K). The first peak indicated a solid state structural phase transition while the second one could be attributed to melting or supplementary materials sup-3 Acta Cryst. (2012). E68, o1114-o1115 solidification.

Refinement
All the hydrogen atoms were found in the difference electron density map and their coordinates were refined independently. The isotropic atomic displacement parameters of the hydrogen atoms were set as 1.2×U eq (N carrier ).

Special details
Experimental. CrysAlisPro (Agilent Technologies, 2010) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement. The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program.