Crystal structure of (1R,5S)-endo-(8-methyl-8-azoniabicyclo[3.2.1]oct-3-yl)ammonium aquatrichloridonitratocopper(II)

The title compound is a salt containing a protonated endo-3-aminotropane cage and a novel anionic copper(II) complex, [CuCl3(NO3)(H2O)]2−.


Figure 1
The endo-3-aminotropane skeleton in the crystal structure of 1. The atomic numbering scheme of the tropane cage is given in accordance with IUPAC nomenclature (Pollini et al., 2006;Kim et al., 2016). Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as fixed-size spheres of 0.15 Å radius. et al., 2016), we report herein for the first time the molecular structure of the endo isomer of 3-aminotropane in its protonated form (see Scheme). In the title compound, (1R,5S)-endo-(8-methyl-8-azoniabicyclo[3.2.1]oct-3-yl)ammonium aquatrichloridonitratocopper(II), 1, the protonated endo-3-aminotropane skeleton ( Fig. 1) is charge-balanced by the [CuCl 3 (NO 3 )(H 2 O)] 2À anion. The anion (Fig. 2) is the first example of a complex in which a copper(II) centre is coordinated to both nitrate and chloride ligands (as well as water). It is noteworthy that the synthesized compound 1 contains the pure endo-3-aminotropane isomer, whereas the starting material, 3-aminotropane dihydrochloride, comprised a mixture of exo and endo isomers. Therefore, selective crystallization of 1 reported herein can be recommended as a simple and effective method for the separation of the exo and endo isomers of 3-aminotropane.

Structural commentary
In the structure of 1, the bicyclic skeleton of 3-aminotropane has a boat-like conformation with the 3-amino group located in the endo position (see Scheme and Fig. 1). Only five examples of structurally characterized endo isomers of 3-aminotropane have been reported previously (Fludzinski et al., 1987;Bradley et al., 1992;Collin et al., 1995;Omae et al., 2002), all of which are N-3-substituted derivatives. The detailed description of the geometry of the endo-3-aminotropane skeleton in 1 can be found in the supporting information. The 3-aminotropane unit has two chiral centres located at the C1 (R) and C5 (S) C atoms. The packing of the 3-aminotropane molecules in the crystal generates an inversion centre establishing the chiral balance between the alternating 3-aminotropane units. The anionic moiety, [CuCl 3 (NO 3 )(H 2 O)] 2À , in the structure of 1 (Fig. 2) is interesting because it is the first reported example of a copper(II) complex coordinated by both chloride and nitrate ligands, in addition to water. The coordination of the Cu II atom by nitrate and water or ammonia ligands is well documented [see, for example, the structures of Cu(NH 3 ) 4 (NO 3 ) 2 (Morosin, 1976;Chukanov et al., 2015) and Cu(NO 3 ) 2 (H 2 O) 2.5 (Garaj & Gazo, 1969)]. In addition, a limited number of isolated chlorideaqua and chlorate-aqua complexes of Cu II have been reported as both neutral clusters, e.g. [Cu(H 2 O) 2 Cl 2 ] (Matkovic et al., 1969;Bhakay-Tamhane et al., 1980) and [Cu(H 2 O) 4 (ClO 3 ) 2 ] (Blackburn et al., 1991), and anionic complexes, e.g.
[CuCl 3 (NO 3 )(H 2 O)] 2À , can be considered as a valuable contribution to the aqueous coordination chemistry of copper(II). The geometry of this unusual cluster ( Fig. 2) can be described as a severely distorted octahedron, with three The molecular structure of the novel copper(II) anionic complex, [CuCl 3 (NO 3 )(H 2 O)] 2À , in 1. Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as fixed-size spheres of 0.15 Å radius.

Supramolecular features
The overall integrity of the crystal structure of 1 is achieved via a complex three-dimensional network of intermolecular hydrogen bonds (Fig. 3). Three types of hydrogen bonding are observed: (i) N-HÁ Á ÁO interactions between the protonated N atom, N8, and the water molecule coordinated to the Cu II atom, (ii) O-HÁ Á ÁCl interactions involving the same water molecule located between two chloride ions and (iii) N-HÁ Á ÁCl interactions between the protonated amino group NH 3 + and chloride ions Cl1 and Cl3 (Table 1).

Synthesis and crystallization
106.6 mg (0.5 mmol) of 3-aminotropane dihydrochloride (a mixture of the 3-exo and 3-endo isomers, Sigma-Aldrich) was dissolved in 1 ml of deionized water. 60.4 mg (0.25 mmol) of Cu(NO 3 ) 2 Á3H 2 O (reagent grade) was dissolved in another 1 ml aliquot of water. On mixing the two solutions, a transparent pale-yellow-green solution was formed. Light-green needles of 1 were grown by slow evaporation of the solution at room temperature.

Refinement
H atoms at the protonated N8 and N9 atoms and water molecule OW1 were refined freely, whereas H atoms on C atoms were refined based on a riding model. Crystal data, data collection and structure refinement details are summarized in

(1R,5S)-endo-(8-Methyl-8-azoniabicyclo[3.2.1]oct-3-yl)ammonium aquatrichloridonitratocopper(II)
Crystal data (C 8  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.