Poly[[(μ4-1,3,5-triamino-1,3,5-trideoxy-cis-inositol)sodium] bromide]

In the structure of the title compound, {[Na(C6H15N3O3)]Br}n, the sodium cation and the bromide anion are both located on threefold rotation axes. The sodium cation is bonded to the three hydroxy groups of one 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) ligand, with the taci ligand residing around the same threefold rotation axis as the sodium ion. The coordination sphere of the sodium ion is completed by three amino groups of three neighbouring taci molecules. Hence, this type of coordination constitutes a three-dimensional open framework with channels along the c axis which are filled with the bromide counter-anions. Each bromide ion forms three symmetry-related hydrogen bonds to both the hydroxy and the amino groups of neighbouring taci ligands.


Related literature
The crystal structure of an Na-bis-taci complex has been reported by Bartholomä et al. (2010). Puckering parameters were calculated according to Cremer & Pople (1975). For a preliminary preparation and characterization of the title compound, see: Egli (1994). For a general overview of the coordination chemistry of taci, see: Hegetschweiler (1999). The crystal structure of a Cu II -taci complex has been reported by Reiss et al. (1998). For the crystal structure of a monoprotonated taci salt, see: Reiss et al. (1999).
In the title compound, [Na(C 6 H 15 N 3 O 3 )] + Br -, the cation, anion and the taci ligand have site symmetry 3. The taci ligand also adopts a chair conformation with axial hydroxy groups, which bind to the Na + cation (Na-O distance: 2.409 (4)Å).
Interlinking of the Na + cation to three equatorial amino groups of three neighbouring taci ligands (Na-N distance: 2.556 (4)Å) generates a distorted octahedral coordination geometry around the sodium ion. Due to symmetry, the three oxygen and the three nitrogen donors form each two parallel, equilateral triangles with a twist angle τ of 56.4°. This value indicates that the fac-NaO 3 N 3 coordination geometry adopts C 3v symmetry quite closely. The bromide anion is hydrogenbonded to three hydroxy groups of three adjacent taci ligands. Additionally, three N-H···Br contacts are formed (see Table 1). These N-H···Br contacts may be interpreted as weak hydrogen bonds. The three (N-)H and the three (O-)H hydrogen atoms form again two parallel, equilateral triangles with a twist angle τ = 32.4°. The six hydrogen atoms, which encapsulate the bromide ion, constitute thus a polyhedron which is just an intermediate form between a trigonal prism (τ = 0°) and a trigonal antiprism (τ = 60°). Notably, the bromide ion is not located in the centre of this polyhedron. It is significantly displaced towards the three (O-)H hydrogen atoms. Inspection of the structure further reveals an intermolecular N···O separation of 2.831 (6)Å, a value which falls in a range expected for N-H···O hydrogen bonding. However, the corresponding N-H···O angle of 110 (6)° is very acute and would not be in agreement with such an interpretation.

Experimental
The title compound was first isolated unintentionally by Egli (1994) in the reaction of K 2 ReBr 6 , NaOCH 3 and taci. In our study, it was prepared by adding equimolar amounts of NaBr and taci in small portions to boiling MeOH until a saturated solution was obtained. The solution was filtered hot and was allowed to cool slowly to room temperature, yielding colourless single crystals suitable for crystal structure analysis.

Refinement
All hydrogen atoms were identified in difference syntheses. In the latest stages of refinement, the coordinates of the Nand C-bonded hydrogen atoms were refined, whereas the coordinates of the (O-)H hydrogen atom had to be supplementary materials sup-2 Acta Cryst. (2013). E69, m185-m186 constrained using the AFIX 83 option of the SHELXL program. The N-H bond lengths were restrained to 0.90Å. All U iso values, besides those of the CH groups, were refined freely.

Figure 1
Ellipsoid plot and numbering scheme of a Br anion and an Na(taci) moiety together with the coordinating amino groups of three additional, neighbouring taci units. Displacement parameters are given at the 50% probability level.  Section of the extended network of the title compound viewed along the c axis.

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.  (12)