Crystal structure of octane-1,8-diaminium 4,4′-(diazene-1,2-diyl)dibenzoate monohydrate

The preparation and the crystal structure of octane-1,8-diaminium 4,4′-azinodibenzoate monohydrate are reported.


Structural commentary
The asymmetric unit ( Fig. 1) consists of two halves of octane 1,8-diaminium dications, one 4,4 0 -azinodibenzoic dianion and one water molecule. Bond lengths and angles of the dication and dianion are in the expected ranges. One of the octane ISSN 2056-9890 1,8-diaminium dications shows a fully extended all-trans conformation with torsion angles close to 180 (Table 1). The second cation has its two terminal torsion angles N6-C7-C8-C9 synclinal with a value of À76.89 (12) . The fully extended conformation corresponds to the most stable one, compared to the arrangement with synclinal torsion angles, as shown from DFT calculations and a database survey performed on ,!-alkyldiaminium cations (Brozdowska & Chojnacki, 2017). The less energetically favorable gauche conformation is presumably stabilized by the charge-assisted hydrogen-bonded network.
The geometry of the 4,4 0 -azinodibenzoic dianion is characterized by the presence of two benzoic acid residues linked via a trans-configurated azo group is consistent with known data (Ferná ndez et al., 2015;. The angle between the phenyl rings of 10.22 (4) is consistent with a small deviation from planarity of the azobenzene moiety. The carboxylate groups are inclined to the molecular mean plane at angles of 38.40 (3) (O11/C12/O13) and 16.53 (5) (O29/ C28/O30).

Supramolecular features
In addition to the electrostatic interactions, the anions and cations are connected by charge-assisted N-HÁ Á ÁO hydrogen bonds ( Table 2). The complex pattern of hydrogen bonds also includes the water molecules. Therefore, the 4,4 0 -azinodibenzoic dianion is linked through hydrogen bonds with three cations on one side and with two cations and two water molecules on the other side. Anions and cation stack in twodimensional arrays in the ab plane separated by a zone with  Table 1 Selected torsion angles ( ).

Figure 2
Projection along the b-axis direction showing the packing in layers consolidated by the hydrogen-bond network (dotted lines). Hydrogen atoms not involved in hydrogen bonds and hanging hydrogen bonds are omitted for clarity.

Figure 3
Partial packing view along the b-axis direction showing the R 4 4 (12) graphset motifs. Hydrogen atoms not involved in hydrogen bonds and hanging hydrogen bonds have been omitted for clarity.

Figure 1
Molecular structure and atom-labelling scheme of (I). Displacement ellipsoids are drawn at the 50% probability level and hydrogen bonds are shown as dotted lines. [Symmetry codes: (i) 1 À x, Ày, 2 À z; (ii) Àx, 1 À y, Àz.] the hydrogen-bonded network involving the ionized amino and carboxylic groups and the water molecules (Fig. 2). This network contains two 12-membered rings comprising either two cations and two anions or two cations, two anions and two water molecules (Fig. 3), according to the graph set descriptor R 4 4 (12) (Etter et al., 1990).  (Lemmerer & Billing, 2012;Smith et al., 2017), and more complex systems where the diaminium cations are encapsulated in a macrocycle (Kim et al., 2009;Yu et al., 2014). A similar search for 4,4 0 -azinodibenzoic acid and its salts returned 43 entries, including the structure of the simple acid (Yu & Liu, 2009). The dianion has been also used as linker to prepare MOF or coordination frameworks (see, for example, Hou et al., 2013, Zhang et al., 2016, Guo et al., 2013and Deng et al., 2015, and co-crystallized to give gelator salts (

Synthesis and crystallization
Crystals of the title compound were obtained by the dropwise addition with intensive stirring of 5 ml of 0.10 M aqueous 1,8octamethylenediamine into 25 ml of 0.02 M aqueous 4,4 0 -dicarboxyazobenzene disodium salt at room temperature. The final solution (pH 12.5) was allowed to partly evaporate at room temperature and atmospheric pressure. The resulting orange oblong crystals in the form of thin narrow leaves up to 1 cm long were gently removed from the liquid phase and airdried on filter paper.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms bound to nitrogen or oxygen atoms were located from difference syntheses and refined without any restraints. Hydrogen atoms linked to carbon atoms were included using an appropriate riding model (AFIX 43 and AFIX 23 for aromatic and methylene hydrogen atoms respectively) with C-H = 0.95-0.99 Å and U iso (H) = 1.2U eq (C).

Computing details
Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009) and publCIF (Westrip, 2010).  (17) 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.