Crystal structure of 1,4,8,11-tetramethyl-1,4,8,11-tetraazoniacyclotetradecane bis(perchlorate) dichloride from synchrotron X-ray data

In the title salt, [C14H36N4]4+·2ClO4 −·2Cl−, the macrocyclic cations lie about an inversion center. In the crystal, N–H⋯Cl, C–H⋯Cl and C–H⋯O hydrogen bonds connect the cations and anions, forming a three-dimensional network.

The crystal structure of title salt, C 14 H 36 N 4 4+ Á2ClO 4 À Á2Cl À , has been determined using synchrotron radiation at 220 K. The structure determination reveals that protonation has occurred at all four amine N atoms. The asymmetric unit contains one half-cation (completed by crystallographic inversion symmetry), one perchlorate anion and one chloride anion. A distortion of the perchlorate anion is due to its involvement in hydrogen-bonding interactions with the cations. The crystal structure is consolidated by intermolecular hydrogen bonds involving the 1,4,8,11-tetramethyl-1,4,8,11-tetraazoniacyclotetradecane N-H and C-H groups as donor groups, and the O atoms of the perchlorate and chloride anion as acceptor groups, giving rise to a three-dimensional network. Tetraazamacrocycle 1,4,8,4,8,C 14 H 32 N 4 ) is one of the most useful azamacrocycles because of its ability to act as an effective metal-ion binding site and its basic properties. N-Substituted TMC is a basic amine that may form a dication, C 14 H 34 N 4 2+ , or a tetracation, C 14 H 36 N 4 4+ , in which the N-H bonds are generally active in hydrogen-bond formation. These di-or tetraammonium cations may be suitable for the removal of toxic heavy-metal ions. Because of a difference in the chirality of the secondary NH centers, the macrocyclic compounds can exhibit five conformations, viz. trans-I (RSRS), trans-II (RSRR), trans-III (RRSS), trans-IV (SRRS) and trans-V (RRRR) (Choi, 2009 (Lee et al., 1986), [Cu(TMC)](ClO 4 ) 2 (Maimon et al., 2001), [Ag(TMC)](ClO 4 ) 2 (Po et al., 1991), [Cu(NCS)(TMC)]ClO 4 (Lu et al., 1998) and [Cu(TMC)](BF 4 ) 2 (Bucher et al., 2001b) have been characterized crystallographically. In addition, firstrow transition-metal complexes of the form [M II Cl(TMC)] + [M = Zn (Alcock et al., 1978), Mn (Bucher et al., 2001a), Ni (Nishigaki et al., 2010), Fe (Bedford et al., 2016) and Co (Van Heuvelen et al., 2017)] have been determined. Two independent ring conformations, trans-III and trans-IV, in the crystal structure of free TMC were also found (Willey et al., 1994), but there is no report of a structure with any combination of the 1,4,8,11-tetramethyl-1,4,8,11-tetraazoniacyclotetradecane cation and ClO 4 À and Cl À anions. We report here the preparation of a new compound [H 4 TMC](ClO 4 ) 2 Cl 2 , (I), and ISSN 2056-9890 its structural characterization by synchrotron single-crystal X-ray diffraction.

Figure 1
The structures of the molecular components in (I), drawn with displacement ellipsoids at the 50% probability level. Dashed lines represent hydrogen-bonding interactions and primed atoms are related by the symmetry operation (Àx + 1, Ày + 1, Àz).
The N-HÁ Á ÁCl and C-HÁ Á ÁCl hydrogen bonds link the two Cl À anions to the C 14 H 36 N 4 4+ cation while C-HÁ Á ÁO hydrogen bonds interconnect neighboring cations with the ClO 4 À anions. An extensive array of these contacts generates a three-dimensional network of molecules, and these hydrogenbonding interactions help to consolidate the crystal structure.  (Boag et al., 2000) and (C 14 H 32 N 4 ) (Willey et al., 1994). However, the crystal structure of the title compound had not been deposited until now. The tetra-protonated amine of the title compound has a trans-IV conformation, which is comparable to the trans-

Synthesis and crystallization
The free ligand TMC (98%) was purchased from Sigma-Aldrich and used without further purification. All chemicals were reagent grade materials, and were used as received. TMC (0.128 g, 0.5 mmol) was dissolved in 15 mL of 6 M HCl, and 5 mL of a saturated solution of sodium perchlorate including chromium trioxide (0.1 g, 1 mmol) was added to the resulting solution at 298 K. The mixture was stirred for 2 h and the solution was filtered. Block-like pale yellow crystals of (I) suitable for X-ray structural analysis were unexpectedly obtained from the solution at 298 K over a period of a few days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.97-0.98 Å and N-H = 0.99 Å , and with U iso (H) values of 1.5 and 1.2 times the U eq of the parent atoms.

1,4,8,11-Tetramethyl-1,4,8,11-tetraazoniacyclotetradecane bis(perchlorate) dichloride
Crystal data 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.