Crystal structure of 3,14-dimethyl-2,6,13,17-tetraazoniatricyclo[16.4.0.07,12]docosane tetrachloride tetrahydrate from synchrotron X-ray data

In this hydrated 2,6,13,17-tetraazoniatricyclo[16.4.0.07,12]docosane tetrachloride salt, the cation lies about an inversion center. In the crystal, N—H⋯Cl, O–H⋯Cl and N—H⋯O hydrogen bonds connect the anions, cations and water molecules, forming a three-dimensional network.


Chemical context
The macrocycle 3, 14-dimethyl-2,6,13,17-tetraazatricyclo-(16.4.0.0 7,12 )docosane (C 20 H 40 N 4 , L) is a strongly basic amine capable of forming the [C 20 H 42 N 4 ] 2+ dication or the [C 20 H 44 N 4 ] 4+ tetracation in which all of the N-H bonds are generally available for hydrogen-bond formation. These di-or tetraammonium cations may be suitable for the removal of toxic heavy metal ions from water. The macrocycle L contains a cyclam backbone with two cyclohexane subunits. Methyl groups are attached to the 3 and 14 carbon atoms of the propyl chains that bridge opposite pairs of N atoms in the structure.  (Choi et al., 2006(Choi et al., , 2007(Choi et al., , 2012aRoss et al., 2012). In these Cu II and Zn II complexes, the macrocyclic ligands adopt their most stable trans-III configurations. The crystal structures of the di-cations C 20 H 40 N 4 Á2C 11 H 10 O (Choi et al., 2012c) and [C 20 H 42 N 4 ](SO 4 )Á2MeOH (White et al., 2015) have also been reported. As part of our research program in this area, we report here the preparation of the new tetracationic compound, [C 20 H 44 N 4 ]Cl 4 Á4H 2 O, (I), as the hydrated chloride salt and its structural characterization by synchrotron single-crystal X-ray diffraction.

Structural commentary
The title compound contains a positively charged macrocyclic cation, 4Cl À anions and four solvent water molecules and was ISSN 2056-9890 characterized during studies of the macrocyclic ligand and its copper(II) complexes. An ellipsoid plot of the molecular components in (I) with the atom-numbering scheme is shown in Fig. 1. The asymmetric unit consists of one half of the macrocycle, which lies about a center of inversion, two chloride anions and two solvent water molecules. The four N atoms are coplanar, and the two methyl substituents are anti with respect to the macrocyclic plane as a result of the molecular inversion symmetry. The six-membered cyclohexane ring is in a stable chair conformation. Within the centrosymmetric tetra-protonated amine unit [C 20 H 44 N 4 ] 4+ , the C-C and N-C bond lengths vary from 1.522 (2) to 1.542 (2) Å and from 1.506 (2) to 1.522 (2) Å , respectively. The ranges of N-C-C and C-N-C angles are 106.85 (10) to 114.32 (11) and 116.70 (10) to 118.89 (10) , respectively. The bond lengths and angles within the [C 20 H 44 N 4 ] 4+ tetra-cation are comparable to those found in the free ligand or the di-cation in C 20 H 40 N 4 Á2C 11 H 10 O (Choi et al., 2012c), [C 20 H 42 N 4 ](SO 4 )Á-2MeOH (White et al., 2015) and [C 20 H 42 N 4 ][Fe{HB(pz) 3 }-(CN) 3 ] 2 Á2H 2 OÁ2MeOH (Kim et al., 2004).

Supramolecular features
Extensive O-HÁ Á ÁCl, N-HÁ Á ÁCl and N-HÁ Á ÁO hydrogenbonding interactions occur in the crystal structure ( Table 1). All of the Cl À anions and the O atoms of the water molecules serve as hydrogen-bond acceptors. O-HÁ Á ÁCl hydrogen bonds link the water molecules to the neighboring Cl À anions, while N-HÁ Á ÁCl and N-HÁ Á ÁO hydrogen bonds interconnect the [C 20 H 44 N 4 ] 4+ cations with both anions and water molecules ( Figs. 1 and 2). The hydrogen atoms on N1 and N2 both form bifurcated hydrogen bonds with O and Cl atoms. The extensive array of these contacts generates a three-dimensional network structure (Fig. 2), and these hydrogen-bonding interactions help to stabilize the crystal structure.  Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of compound (I), drawn with displacement ellipsoids at the 50% probability level. Dashed lines represent hydrogenbonding interactions and primed atoms are related by the symmetry code (1 À x, 1 À y, 1 À z).
reported previously. However, to our knowledge no crystal structure of any compound with [C 20 H 44 N 4 ] 4+ has been reported.

Synthesis and crystallization
Commercially available trans-1,2-cyclohexanediamine and methyl vinyl ketone (Sigma-Aldrich) were used as provided. All chemicals were reagent grade and used without further purification. As a starting material, the macrocycle 3,14dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.0 7,12 )docosane was prepared according to a published procedure (Kang et al., 1991). A solution of the macrocyclic ligand (0.084 g, 0.25 mmol) in water (10 mL) was added dropwise to a stirred solution of CuCl 2 Á2H 2 O (0.085 g, 0.5 mmol) in water (15 mL). The solution was heated for 1 h at 338 K. After cooling to 298 K, the pH was adjusted to 3.0 with 1.0 M HCl. The solution was filtered and left at room temperature. Colourless crystals suitable for X-ray analysis were obtained unexpectedly from the solution over a period of a few days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All C and N-bound H atoms in the complex were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances of 0.97-0.99 Å , an N-H distance of 0.9 Å and with U iso (H) values of 1.2U eq (C, N) and 1.5U eq (C-methyl   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.