Crystal structure of 1,4,8,11-tetraazoniacyclotetradecane bis(dichromate) monohydrate from synchrotron data

In the title hydrated salt, (C10H28N4)4+·2[Cr2O7]2−·H2O, the two unique cations lie about an inversion centre. In the crystal, O—H⋯O and N—H⋯O hydrogen bonds connect the anions, cations and water molecule, forming a three-dimensional network


Structural commentary
An ellipsoid plot of the molecular components of (I) along with the atom-numbering scheme is shown in Fig. 1. The asymmetric unit comprises of two half-cations (both completed by crystallographic inversion symmetry), two dichromate anions and one water molecule. Within the centrosymmetric tetra-protonated amine unit, (C 10 H 28 N 4 ) 4+ , the C-C and N-C bond lengths range from 1.491 (3) to 1.520 (3) Å and from 1.489 (3) to 1.524 (3) Å , respectively. The range of N-C-C and C-N-C angles is 109.84 (19) (Moon & Choi, 2016).

Figure 2
The crystal packing in compound (I), viewed perpendicular to the bc plane. Dashed lines represent N-HÁ Á ÁO (pink) and O-HÁ Á ÁO (cyan) hydrogen-bonding interactions, respectively. H atoms bound to C atoms have been omitted.

Figure 1
The structures of the molecular components in (I), drawn with displacement ellipsoids at the 60% probability level.

Supramolecular features
Extensive N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bonding interactions occur in the crystal structure (Table 1). Two O-HÁ Á ÁO hydrogen bonds link the water molecule to two neighboring [CrO 7 ] 2À anions while N-HÁ Á ÁO hydrogen bonds interconnect the (C 10 H 28 N 4 ) 4+ cations with both anions ( Figs. 1 and 2). An extensive array of these contacts generates a three-dimensional network ( Fig. 2) and, apart from Coulombic interactions, these hydrogen-bonding interactions help to stabilize the crystal structure.

Synthesis and crystallization
Cyclam (98%) was purchased from Sigma-Aldrich and used without further purification. All other chemicals were reagentgrade materials, and were used as received. 0.102 g of chromium trioxide (1 mmol, Sigma-Aldrich) was dissolved in 20 ml of water and 0.012 g of cyclam (0.06 mmol, Sigma-Aldrich) was added at room temperature. The mixture was stirred for 30 minutes and the resulting solution was filtered. The neat filtrate was allowed to stand for one week to give block-like yellow crystals of (I) suitable for X-ray structural analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.99 Å and N-H = 0.91 Å , respectively, and with U iso (H) values of 1.2U eq of the parent atoms. The hydrogen atoms of the solvent water molecule were assigned based on a difference-Fourier map, and were refined with distance restraints of 0.84 (2) Å (using DFIX and DANG commands), and with U iso (H) values of 1.5U eq of the parent atom. The remaining maximum and minimum electron densities in the final Fourier map are located 0.85 and 0.54 Å , respectively, from the Cr1B site. Six reflections with a poor agreement between measured and calculated intensities were omitted from the final refinement cycles. Data collection: PAL BL2D-SMDC (Shin et al., 2016); cell refinement: HKL3000sm (Otwinowski & Minor, 1997); data reduction: HKL3000sm (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXT2015 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2015 (Sheldrick, 2015b); molecular graphics: DIAMOND (Putz & Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010).

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.