Propane-1,2-diaminium selenite monohydrate

The asymmetric unit of (I) contains one C3H12N2 2+ cation, one SeO2 2 anion and a water molecule (Fig. 1). The geometric parameters for the organic cation are unexceptional (Lee & Harrison, 2003a). This species is chiral (C1 has S configuration in the selected asymmetric unit), but crystal symmetry generates a 50:50 mix of enantiomers, consistent Received 15 April 2005 Accepted 22 April 2005 Online 7 May 2005

The asymmetric unit of (I) contains one C 3 H 12 N 2 2+ cation, one SeO 2 2À anion and a water molecule (Fig. 1). The geometric parameters for the organic cation are unexceptional (Lee & Harrison, 2003a). This species is chiral (C1 has S configuration in the selected asymmetric unit), but crystal symmetry generates a 50:50 mix of enantiomers, consistent with the racemic starting material. The selenite group in (I) shows its standard (Lee & Harrison, 2003) pyramidal geometry (Table 1) [average Se-O = 1.687 (2) Å ], with the Se atom displaced from the plane of its three attached O atoms by 0.7213 (12) Å .
As well as electrostatic attractions, the component species in (I) interact by means of a network of N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds ( Table 2). The selenite anions and water molecules are linked into a polymeric chain in the [010] direction by hydrogen bonds (Fig. 2). The organic species interacts with the selenite/water chains by way of N-HÁ Á ÁO hydrogen bonds (Table 2). All six of the -NH 3 + H atoms are involved in these links [mean HÁ Á ÁO = 1.89 Å , N-HÁ Á ÁO = 165 and NÁ Á ÁO = 2.777 (3) Å ]. These interactions result in (101) selenite/water/aminium layers sandwiched between the carbon backbones of the organic groups (Fig. 3), which themselves interact by way of van der Waals forces.

Experimental
An aqueous 0.5 M propane-1,2-diamine solution (10 ml) was added to aqueous 0.5 M H 2 SeO 3 solution (10 ml, dissolved SeO 2 ) to result in a clear solution. A mass of colourless platy crystals of (I), with a palepink tinge arising from a surface coating, grew as the water evaporated over the course of a few days.

Figure 2
Detail of a hydrogen-bonded selenite/water chain in (I). Symmetry codes are as in Table 2 [additionally: (v) x, 1 + y, z]. Hydrogen bonds are indicated by dashed lines.
The non-standard P2/n setting of the space group was chosen in preference to P2/c to avoid a unit cell with a very obtuse angle of 133.6 . The water H atoms were found in a difference map and refined as riding in their as-found relative positions (Table 2). H atoms bonded to C and N atoms were placed in idealized positions (C-H = 0.98-1.00 Å and N-H = 0.91 Å ) and refined as riding, allowing for free rotation of the rigid -XH 3 (X = C3, N1 and N2) groups. The constraint U iso (H) = 1.2U eq (carrier) or U iso (H) = 1.2U eq (methyl carrier) was applied as appropriate.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq