1,3-Dinitrosoimidazolidine

The title compound, C3H6N4O2, exhibits partial disorder with the refined occupancy ratios of the two components being 0.582 (5):0.418 (5). In the major component, the nitroso groups have a relative syn spatial arrangement [O=N⋯N=O pseudo-torsion angle = 1.1 (4)°], whereas the other component has an anti disposition [177.6 (1)°]. The N—N=O moieties are almost coplanar with a dihedral angle of 5.3 (3)°, while in the minor occupied set of atoms, this angle is 8 (1)°. In both components, the imidazolidine ring adopts a twisted conformation on the C—C bond and the crystal structure shows the strain of this ring according to the N—CH2—CH2—N torsion angles [25.9 (5) and −23.8 (7)°]. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds.

The title compound, C 3 H 6 N 4 O 2 , exhibits partial disorder with the refined occupancy ratios of the two components being 0.582 (5):0.418 (5). In the major component, the nitroso groups have a relative syn spatial arrangement [O NÁ Á ÁN O pseudo-torsion angle = 1.1 (4) ], whereas the other component has an anti disposition [177.6 (1) ]. The N-N O moieties are almost coplanar with a dihedral angle of 5.3 (3) , while in the minor occupied set of atoms, this angle is 8 (1) . In both components, the imidazolidine ring adopts a twisted conformation on the C-C bond and the crystal structure shows the strain of this ring according to the N-CH 2 -CH 2 -N torsion angles [25.9 (5) and À23.8 (7) ]. In the crystal, molecules are linked by weak C-HÁ Á ÁO hydrogen bonds.

Related literature
For a related structure, see: Rivera et al. (2011). For the synthesis of the title compound, see: Rivera et al. (1997). For ring conformations, see Cremer & Pople (1975). For chemical background on the synthesis and uses of N-nitroso amines, see: Di Salvo et al. (2008).  Table 1 Hydrogen-bond geometry (Å , ). Data collection: CrysAlis PRO (Agilent, 2010); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: JANA2006 (Petříček et al., 2006); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: JANA2006.  Salvo et al., 2008). Our group has previously explored the reaction of nitrous acid with cyclic aminals which actually are tertiary amines (Rivera et al., 1997(Rivera et al., , 2011. Earlier we reported the synthesis and complete characterization by NMR of the title compound 1,3-dinitrosoimidazolidine, obtained by the nitrosation reaction of the cyclic aminal 1, 3,6,8-tetraazatricyclo[4.4.1.1. 3,8 ]dodecane (Rivera et al., 1997). NMR experiments of this compound evidenced the existence of a mixture of three isomers: syn-cis, anti, and cis-trans with a ratio of 31:50:19 respectively (Rivera, et al. 1997). However, a recently investigation of (3aRS,7aRS)-1,3-dinitrosooctahydro-1H-benzimidazole, we found that the nitroso groups of this analogous X-ray crystal structure are on a syn-cis disposition (Rivera, et al. 2011). This result suggests that the orientation of the nitroso groups on the imidazolidine ring is largely influenced by their molecular skeletons. To identify the orientation of nitroso groups, we synthesized the title compound and investigated its crystal structure.

D-HÁ
X-Ray analysis confirms the molecular structure and atom connectivity as illustrated in Fig. 1. The bond lengths N-C1 and N-NO are normal and comparable to the corresponding values observed in the related structure (Rivera, et al. 2011). The title compound are disordered over two sets of sites [site occupancies = 0.588 (6) and 0.412 (6)

Experimental
For the originally reported synthesis, see: Rivera et al. (1997). Single crystals of the title compound were obtained by recrystallization from EtOH solution (m.p 318 K).

Refinement
All hydrogen atoms were positioned geometrically and treated as riding on their parent atoms. The isotropic atomic displacement parameters of hydrogen atoms were set to 1.2×U eq of the parent atom.
The molecule is disordered over two positions with occupancies 0.588 (6):0.412 (6). Selected atoms of both components were refined isotropically as anisotropic refinement lead to unreasonable ADPs.
As the structure contains only light atoms, the Friedel-pairs were merged and the Flack parameter has not been determined.

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.  (16) Geometric parameters (Å, º)