Melaminium iodide monohydrate

In the title melaminium salt, 2,4,6-triamino-1,3,5-triazin-1-ium iodide monohydrate, C3H7N6 +·I−·H2O, the components are linked via N—H⋯O, N—H⋯N, O—H⋯I and N—H⋯I hydrogen bonds. All of the H atoms of the melaminium cation are involved in hydrogen bonds. The melaminium cations are interconnected by four N—H⋯N hydrogen bonds, forming ribbons along [111]. The water molecules connected by N—H⋯O hydrogen bonds also form part of these ribbons. The ribbons are interconnected by other hydrogen bonds (O—H⋯I and N—H⋯I), as well as by π–π interactions [centroid–centroid distance = 3.6597 (17) Å].


Comment
The melamine molecule and its organic and inorganic complexes or salts can develop supramolecular structures via multiple hydrogen-bonding systems by self-assembly of components which contain abundant hydrogen-bonding sites (Janczak et al., 2001;Athikomrattanakul et al., 2007). The present study is a part of systematic investigation of ferroelectric materials Hang et al., 2009) that include metal-organic coordination compounds with organic ligands or are related to the structures with both organic and inorganic building fragments.
The compound was characterized by the X-ray powder diffraction (XRPD) at room temperature. The pattern calculated from the single-crystal X-ray data was in a good agreement with the observed at to the peak positions but with different peak intensities.
The structure is composed of the melaminium cations, iodide anions and the water molecules (Fig. 1). The melaminium cation is protonated at only one melamine site. The six-membered melaminium ring exhibits distortions from the regular hexagonal form. The internal C-N-C angle at the protonated N atom (119.5 (2)°) is greater than the other two C-N-C angles of the ring (115.5 (2)°) and the internal N-C-N angles involving the unprotonated ring N atoms (126.1 (2)°) are obviously larger than those containing protonated and unprotonated N atoms (121.4 (2)°) . forming ribbons parallel to (1 1 1). The water molecules connected by N-H···O hydrogen bonds (Tab. 1) form also a part of these ribbons. The ribbons are interconnected by other hydrogen bonds that involve Ias well as by π-electron ring -π-electron ring interactions with the distance between the centroids of the neighbour melaminium rings (1-x,1-y,1-z) equal to 3.6597 (17)  Dielectric studies (capacitance and dielectric loss measurements) were performed on powder samples which have been pressed into tablets with conducting carbon glue deposited on their faces. The automatic impedance TongHui2828 Analyzer has been used (Uthrakumar et al., 2008). In the measured temperature range from 80 to 450 K (m.p. > 470 K), the temperature dependence of the relative permittivity at 1 MHz varied smoothly from 3.9 to 5.2 in the title compound. No dielectric anomaly has been observed. Fig. 1. The title molecules with the atomic numbering scheme. The displacement ellipsoids are drawn at the 30% probability level. 2,4,6-triamino-1,3,5-triazin-1-ium iodide monohydrate

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. 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 Rfactors(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