The first molecular structure containing four hydroperoxo groups: piperazine-2,3,5,6-tetrayl tetrahydroperoxide pyrazine disolvate dihydrate

# 2006 International Union of Crystallography All rights reserved The reaction of pyrazine with hydrogen peroxide resulted in piperazine-2,3,5,6-tetrayl tetrahydroperoxide, crystallizing as its pyrazine disolvate dihydrate, C4H10N2O8 2C4H4N2 2H2O. In the crystal structure, the tetraperoxo molecules, which possess a crystallographically imposed centre of symmetry, are linked into a three-dimensional network by hydrogen-bonding interactions involving the pyrazine and water molecules.

The reaction of pyrazine with hydrogen peroxide resulted in piperazine-2,3,5,6-tetrayl tetrahydroperoxide, crystallizing as its pyrazine disolvate dihydrate, C 4 H 10 N 2 O 8 Á2C 4 H 4 N 2 Á2H 2 O. In the crystal structure, the tetraperoxo molecules, which possess a crystallographically imposed centre of symmetry, are linked into a three-dimensional network by hydrogen-bonding interactions involving the pyrazine and water molecules.

Comment
Peroxo derivatives of organic compounds attract particular interest as environmentally friendly bleaching compounds and oxidation agents in organic synthesis (Marwah et al., 2004). As part of our study of organic hydrogen peroxide solvates (Churakov et al., 2004(Churakov et al., , 2005, we tried to investigate the behaviour of small organic donor molecules, such as pyrazine or pyrimidine, in concentrated H 2 O 2 solutions. The unexpected title compound, (I), was formed upon freezing of a pyrazine solution in 50% hydrogen peroxide. The nature of this process remains unclear. The centrosymmetric molecule of (I) (Fig. 1) contains four hydroperoxo substituents. The piperazine ring adopts a chair conformation and all hydroperoxo groups occupy axial positions. Atom N3 is slightly flattened, the sum of valence angles around it being 346.0 . The O-O bond lengths [1.470 (1) and 1.471 (1) Å ] are somewhat longer than the mean value of 1.462 Å found for related compounds (85 entries, 106 fragments) in the Cambridge Structural Database (CSD, Version 5.27 of January 2006;Allen, 2002).
The hydroperoxo atom O3 acts as both donor (for symmetry-related) molecules and acceptor (for water molecules) of hydrogen bonds, forming layers perpendicular to the c axis (Fig. 2). Pyrazine molecules accept hydrogen bonds from the peroxo O4 and water O5 atoms, cross-linking the layers of the main molecules into a three-dimensional network (Fig. 3).
To date, the CSD contains structures of compounds with no more than two hydroperoxo groups. The title compound is the first example of a molecular structure containing four OOH substituents. To the best of our knowledge, (I) is one of the most rich in oxygen organic molecules.

Experimental
Pyrazine (99%) and 50% hydrogen peroxide were purchased from Aldrich. Pyrazine (0.03 g) was dissolved in approximately 1 ml of 50% H 2 O 2 . This solution was stored in a freezer at 255 K. After six months, several tiny crystals were found on the wall of a sample bottle. The amount of crystalline material was not enough to investigate it with usual spectroscopic methods. In order to analyse the mother liquor by NMR, it was evaporated in vacuum and the residual oil was dissolved in D 2 O. Unfortunately, the recorded 1 H and 13 C spectra of this complex mixture were non-interpretable.  Table 1 Hydrogen-bond geometry (Å , ).  (18) 160 (2) Symmetry codes: (i) x À 1; y; z; (ii) x; y þ 1; z þ 1; (iii) Àx; Ày þ 2; Àz þ 2; (iv) x; y; z À 1.

Figure 2
The hydrogen-bonded (dashed lines) layer in (I) perpendicular to the c axis. H atoms not involved in hydrogen bonds have been omitted for clarity.

Figure 3
The crystal packing of (I), viewed approximately along the a axis. Hydrogen bonds are shown as dashed lines. H atoms not involved in hydrogen bonds have been omitted for clarity.
All H atoms were located in a difference Fourier map and refined isotropically.
AVC is grateful to the Russian Science Support Foundation. 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.