Crystal structure of (1R,5S)-endo-(8-methyl-8-azoniabi-cyclo-[3.2.1]oct-3-yl)ammonium aqua-tri-chlorido-nitratocopper(II).

The structure of a salt of diprotonated endo-3-amino-tropane crystallized with a copper(II) anionic cluster is reported, viz. (C8H18N2)[CuCl3(NO3)(H2O)]. Neither ion in the salt has been structurally characterized previously. In the crystal, the ions pack together to form a three-dimensional structure held together by a network of inter-molecular N-H⋯O, O-H⋯Cl and N-H⋯Cl hydrogen-bonding inter-actions. Selective crystallization of the title compound can be considered as a simple method for the separation of the exo and endo isomers of 3-amino-tropane.

Chemical context

The bicyclic ring of tropane [(1R,5S)-8-methyl-8-aza­bicyclo­[3.2.1]octa­ne] is the fuctional core of pharmaceutically important alkaloids, such as atropine, hyoscyamine, scopolamine, cocaine and their semisynthetic derivatives (Pollini et al., 2006 ▸; Kim et al., 2016 ▸). As a consequence, there have been a large number of structural studies devoted to tropane-based compounds. It is surprising, however, that some of the simplest derivatives of tropane, such as 3-amino­tropane, have not been structurally characterized in their unsubstituted forms. The structures of other simple and well-known bicyclic organic compounds have been reported only very recently, including 1,4-di­aza­bicyclo­[3.2.1]octane (Britvin et al., 2017 ▸) and 7-aza­bicyclo­[2.2.1]heptane (7-aza­norbornane) (Britvin & Rumyantsev, 2017 ▸). In the course of our ongoing studies of cage-like heterocyclic amines (Britvin & Lotnyk, 2015 ▸; Britvin 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 [CuCl3(NO3)(H2O)]2− 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.

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.

Figure 2

The mol­ecular structure of the novel copper(II) anionic complex, [CuCl3(NO3)(H2O)]2−, in 1. Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as fixed-size spheres of 0.15 Å radius.

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, [CuCl3(NO3)(H2O)]2−, 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 CuII atom by nitrate and water or ammonia ligands is well documented [see, for example, the structures of Cu(NH3)4(NO3)2 (Morosin, 1976 ▸; Chukanov et al., 2015 ▸) and Cu(NO3)2(H2O)2.5 (Garaj & Gazo, 1969 ▸)]. In addition, a limited number of isolated chloride–aqua and chlorate–aqua complexes of CuII have been reported as both neutral clusters, e.g. [Cu(H2O)2Cl2] (Matkovic et al., 1969 ▸; Bhakay-Tamhane et al., 1980 ▸) and [Cu(H2O)4(ClO3)2] (Blackburn et al., 1991 ▸), and anionic complexes, e.g. [Cu(H2O)2Cl4]2− (Begley et al., 1988 ▸) and [Cu(H2O)2Cl3]− (Wei & Willett, 1996 ▸). Therefore, the new complex anion, viz. [CuCl3(NO3)(H2O)]2−, 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 Cu—Cl bonds [Cu1—Cl1 = 2.3019 (3), Cu1—Cl2 = 2.5856 (4) and Cu1–Cl3 = 2.2499 (3) Å], one Cu—OH2 bond [Cu1—OW1 = 2.0646 (10) Å] and two Cu—O bonds from the asymmetrically bonded NO3 ligand [Cu1—O1 = 1.9923 (9) Å and the very weak Cu1—O2 = 2.609 (1) Å]. Similar bonding of an NO3 group to a CuII centre, with two distinct bond lengths, has been reported, for example, in Cu(NO3)2(H2O)2.5 (Garaj & Gazo, 1969 ▸), anhydrous β-Cu(NO3)2 (Troyanov et al., 1995 ▸) and (NH4)3[Cu(NO3)4](NO3) (Morozov et al., 1998 ▸).

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—H⋯O inter­actions between the protonated N atom, N8, and the water mol­ecule coordinated to the CuII atom, (ii) O—H⋯Cl inter­actions involving the same water mol­ecule located between two chloride ions and (iii) N—H⋯Cl inter­actions between the protonated amino group NH3 + and chloride ions Cl1 and Cl3 (Table 1 ▸).

Figure 3

A network of hydrogen bonds maintains the structural integrity of 1. The bond lengths are given in Table 1 ▸.

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N8—H8⋯OW1i	0.783 (17)	2.236 (17)	2.9600 (15)	154.0 (15)
OW1—HW1A⋯Cl1ii	0.79 (2)	2.33 (2)	3.1145 (11)	172.4 (19)
OW1—HW1B⋯Cl2iii	0.79 (2)	2.30 (2)	3.0851 (11)	179 (2)

Symmetry codes: (i) ; (ii) ; (iii) .

Database survey

Among the 204 structures containing the tropane core in the Cambridge Structural Database (CSD, Version 5.38, latest update May 2017; Groom et al., 2016 ▸), 11 entries contain 3-amino­tropane derivatives, all of which are substituted at the 3-amino group. There are five structures in the CSD and nine in the ICSD (ICSD, 2017 ▸), which contain isolated chloro–aqua complexes of copper(II) (Matkovic et al., 1969 ▸; Bhakay-Tamhane et al., 1980 ▸; Begley et al., 1988 ▸; Wei & Willett, 1996 ▸).

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(NO3)2·3H2O (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 Table 2 ▸.

Table 2

Experimental details

Crystal data
Chemical formula	(C8H18N2)[CuCl3(NO3)(H2O)]
M r	392.16
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	150
a, b, c (Å)	6.2464 (3), 13.5674 (6), 17.4584 (8)
β (°)	100.128 (1)
V (Å3)	1456.50 (12)
Z	4
Radiation type	Mo Kα
μ (mm−1)	2.06
Crystal size (mm)	0.25 × 0.20 × 0.15
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 2015 ▸)
No. of measured, independent and observed [I > 2σ(I)] reflections	16933, 3523, 3382
R int	0.012
(sin θ/λ)max (Å−1)	0.661
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.018, 0.049, 1.05
No. of reflections	3523
No. of parameters	197
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.43, −0.31

Computer programs: APEX2 and SAINT (Bruker, 2015 ▸), SHELXT (Sheldrick, 2015 ▸), SHELXL (Sheldrick, 2015 ▸), Mercury (Macrae et al., 2008 ▸), OLEX2 (Dolomanov et al., 2009 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989017014633/cq2021sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017014633/cq2021Isup2.hkl

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989017014633/cq2021Isup3.mol

CCDC reference: 1571888

Additional supporting information: crystallographic information; 3D view; checkCIF report

(C8H18N2)[CuCl3(NO3)(H2O)]	F(000) = 804
Mr = 392.16	Dx = 1.788 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.2464 (3) Å	Cell parameters from 9865 reflections
b = 13.5674 (6) Å	θ = 2.8–35.0°
c = 17.4584 (8) Å	µ = 2.06 mm−1
β = 100.128 (1)°	T = 150 K
V = 1456.50 (12) Å3	Block, green
Z = 4	0.25 × 0.20 × 0.15 mm

Bruker APEX-II CCD diffractometer	3523 independent reflections
Radiation source: fine-focus sealed tube	3382 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
φ and ω scans	θmax = 28.0°, θmin = 1.9°
Absorption correction: multi-scan SADABS (Sheldrick, 2015)	h = −8→8
	k = −17→17
16933 measured reflections	l = −23→22

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.018	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.049	w = 1/[σ2(Fo2) + (0.0249P)2 + 0.617P] where P = (Fo2 + 2Fc2)/3
S = 1.05	(Δ/σ)max = 0.001
3523 reflections	Δρmax = 0.43 e Å−3
197 parameters	Δρmin = −0.31 e Å−3

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.

	x	y	z	Uiso*/Ueq
C1	0.3006 (2)	0.09472 (10)	0.65317 (7)	0.0272 (3)
H1	0.1897	0.0452	0.6581	0.033*
C2	0.2156 (2)	0.19808 (10)	0.66403 (8)	0.0296 (3)
H2A	0.1662	0.2008	0.7136	0.036*
H2B	0.0906	0.2101	0.6236	0.036*
C3	0.3811 (2)	0.28074 (9)	0.66170 (7)	0.0255 (2)
H3	0.3426	0.3338	0.6949	0.031*
C4	0.6143 (2)	0.24969 (10)	0.69599 (7)	0.0273 (2)
H4A	0.7142	0.2906	0.6733	0.033*
H4B	0.6397	0.2624	0.7515	0.033*
C5	0.66665 (19)	0.14187 (10)	0.68295 (7)	0.0253 (2)
H5	0.8146	0.1257	0.7089	0.030*
C6	0.6311 (2)	0.11169 (11)	0.59713 (8)	0.0323 (3)
H6A	0.7268	0.0578	0.5892	0.039*
H6B	0.6579	0.1668	0.5647	0.039*
C7	0.3908 (3)	0.07923 (11)	0.57794 (8)	0.0347 (3)
H7A	0.3115	0.1189	0.5361	0.042*
H7B	0.3798	0.0105	0.5624	0.042*
N8	0.50100 (18)	0.07935 (8)	0.71434 (6)	0.0239 (2)
C8	0.5664 (3)	−0.02653 (10)	0.72557 (9)	0.0375 (3)
H8A	0.4508	−0.0632	0.7418	0.056*
H8B	0.6950	−0.0313	0.7646	0.056*
H8C	0.5955	−0.0530	0.6774	0.056*
N3	0.3612 (2)	0.32304 (9)	0.58084 (7)	0.0285 (2)
Cu1	0.77174 (2)	0.33409 (2)	0.41227 (2)	0.02287 (5)
Cl1	0.45571 (5)	0.24722 (2)	0.41328 (2)	0.03028 (7)
Cl2	0.84844 (5)	0.40007 (2)	0.55338 (2)	0.03060 (7)
Cl3	0.60443 (6)	0.45734 (2)	0.33880 (2)	0.03453 (8)
N1	0.94979 (18)	0.15675 (8)	0.40161 (7)	0.0286 (2)
O1	0.94479 (15)	0.21792 (7)	0.45717 (5)	0.02895 (19)
O2	0.8758 (2)	0.18232 (10)	0.33464 (7)	0.0465 (3)
O3	1.0312 (2)	0.07521 (9)	0.41756 (10)	0.0614 (4)
OW1	1.05693 (16)	0.38867 (8)	0.38441 (6)	0.02756 (19)
H8	0.484 (3)	0.1001 (12)	0.7547 (10)	0.024 (4)*
H3A	0.374 (3)	0.2818 (15)	0.5454 (11)	0.040 (5)*
HW1A	1.164 (3)	0.3573 (15)	0.3938 (11)	0.042 (5)*
H3B	0.234 (4)	0.3451 (15)	0.5664 (12)	0.050 (6)*
HW1B	1.080 (3)	0.4426 (17)	0.4001 (12)	0.046 (5)*
H3C	0.451 (4)	0.3683 (17)	0.5810 (12)	0.052 (6)*

	U11	U22	U33	U12	U13	U23
C1	0.0225 (6)	0.0289 (6)	0.0282 (6)	−0.0064 (5)	−0.0009 (5)	0.0005 (5)
C2	0.0210 (6)	0.0344 (7)	0.0346 (7)	0.0010 (5)	0.0081 (5)	0.0051 (5)
C3	0.0302 (6)	0.0244 (6)	0.0232 (5)	0.0014 (5)	0.0080 (5)	0.0003 (4)
C4	0.0276 (6)	0.0269 (6)	0.0261 (6)	−0.0073 (5)	0.0010 (5)	0.0004 (5)
C5	0.0187 (5)	0.0295 (6)	0.0271 (6)	−0.0010 (5)	0.0021 (4)	0.0046 (5)
C6	0.0343 (7)	0.0362 (7)	0.0287 (6)	0.0089 (6)	0.0116 (5)	0.0015 (5)
C7	0.0431 (8)	0.0345 (7)	0.0241 (6)	−0.0017 (6)	−0.0006 (5)	−0.0059 (5)
N8	0.0271 (5)	0.0236 (5)	0.0206 (5)	−0.0025 (4)	0.0031 (4)	0.0005 (4)
C8	0.0471 (8)	0.0242 (6)	0.0394 (7)	0.0014 (6)	0.0029 (6)	0.0052 (5)
N3	0.0303 (6)	0.0289 (6)	0.0267 (6)	0.0020 (5)	0.0059 (5)	0.0035 (4)
Cu1	0.01998 (8)	0.02360 (8)	0.02488 (8)	0.00238 (5)	0.00351 (6)	0.00206 (5)
Cl1	0.02233 (14)	0.03309 (16)	0.03568 (16)	−0.00169 (11)	0.00582 (11)	0.00026 (12)
Cl2	0.03173 (16)	0.03230 (16)	0.02900 (15)	−0.00508 (12)	0.00873 (12)	−0.00633 (12)
Cl3	0.03283 (16)	0.02662 (15)	0.04061 (18)	0.00540 (12)	−0.00329 (13)	0.00498 (13)
N1	0.0203 (5)	0.0242 (5)	0.0404 (6)	−0.0028 (4)	0.0033 (4)	−0.0055 (4)
O1	0.0292 (5)	0.0287 (5)	0.0280 (4)	0.0026 (4)	0.0024 (4)	0.0006 (4)
O2	0.0488 (7)	0.0601 (8)	0.0312 (5)	−0.0034 (6)	0.0087 (5)	−0.0084 (5)
O3	0.0518 (7)	0.0272 (6)	0.0952 (11)	0.0092 (5)	−0.0145 (7)	−0.0147 (6)
OW1	0.0238 (5)	0.0249 (5)	0.0342 (5)	0.0009 (4)	0.0057 (4)	0.0006 (4)

C1—H1	0.9800	C7—H7B	0.9700
C1—C2	1.5231 (19)	N8—C8	1.4970 (17)
C1—C7	1.5318 (19)	N8—H8	0.783 (17)
C1—N8	1.5103 (16)	C8—H8A	0.9600
C2—H2A	0.9700	C8—H8B	0.9600
C2—H2B	0.9700	C8—H8C	0.9600
C2—C3	1.5305 (18)	N3—H3A	0.85 (2)
C3—H3	0.9800	N3—H3B	0.85 (2)
C3—C4	1.5333 (18)	N3—H3C	0.83 (2)
C3—N3	1.5086 (16)	Cu1—Cl1	2.3019 (3)
C4—H4A	0.9700	Cu1—Cl2	2.5856 (4)
C4—H4B	0.9700	Cu1—Cl3	2.2499 (3)
C4—C5	1.5247 (18)	Cu1—O1	1.9923 (9)
C5—H5	0.9800	Cu1—OW1	2.0646 (10)
C5—C6	1.5313 (18)	N1—O1	1.2811 (15)
C5—N8	1.5132 (16)	N1—O2	1.2292 (17)
C6—H6A	0.9700	N1—O3	1.2289 (16)
C6—H6B	0.9700	OW1—HW1A	0.79 (2)
C6—C7	1.543 (2)	OW1—HW1B	0.79 (2)
C7—H7A	0.9700
C2—C1—H1	110.7	C6—C7—H7A	110.7
C2—C1—C7	114.95 (11)	C6—C7—H7B	110.7
C7—C1—H1	110.7	H7A—C7—H7B	108.8
N8—C1—H1	110.7	C1—N8—C5	101.59 (9)
N8—C1—C2	107.63 (10)	C1—N8—H8	110.9 (12)
N8—C1—C7	101.74 (10)	C5—N8—H8	109.7 (12)
C1—C2—H2A	108.6	C8—N8—C1	113.48 (10)
C1—C2—H2B	108.6	C8—N8—C5	113.39 (11)
C1—C2—C3	114.80 (10)	C8—N8—H8	107.7 (12)
H2A—C2—H2B	107.5	N8—C8—H8A	109.5
C3—C2—H2A	108.6	N8—C8—H8B	109.5
C3—C2—H2B	108.6	N8—C8—H8C	109.5
C2—C3—H3	106.6	H8A—C8—H8B	109.5
C2—C3—C4	112.83 (10)	H8A—C8—H8C	109.5
C4—C3—H3	106.6	H8B—C8—H8C	109.5
N3—C3—C2	111.03 (11)	C3—N3—H3A	115.4 (13)
N3—C3—H3	106.6	C3—N3—H3B	109.3 (15)
N3—C3—C4	112.70 (10)	C3—N3—H3C	109.5 (15)
C3—C4—H4A	108.6	H3A—N3—H3B	102.9 (18)
C3—C4—H4B	108.6	H3A—N3—H3C	109.8 (19)
H4A—C4—H4B	107.5	H3B—N3—H3C	110 (2)
C5—C4—C3	114.79 (10)	Cl1—Cu1—Cl2	100.684 (12)
C5—C4—H4A	108.6	Cl3—Cu1—Cl1	94.122 (14)
C5—C4—H4B	108.6	Cl3—Cu1—Cl2	105.990 (13)
C4—C5—H5	110.8	O1—Cu1—Cl1	89.92 (3)
C4—C5—C6	113.86 (11)	O1—Cu1—Cl2	84.38 (3)
C6—C5—H5	110.8	O1—Cu1—Cl3	167.91 (3)
N8—C5—C4	107.79 (10)	O1—Cu1—OW1	86.88 (4)
N8—C5—H5	110.8	OW1—Cu1—Cl1	164.17 (3)
N8—C5—C6	102.33 (10)	OW1—Cu1—Cl2	94.43 (3)
C5—C6—H6A	110.8	OW1—Cu1—Cl3	86.14 (3)
C5—C6—H6B	110.8	O2—N1—O1	118.83 (11)
C5—C6—C7	104.90 (11)	O3—N1—O1	118.42 (13)
H6A—C6—H6B	108.8	O3—N1—O2	122.75 (13)
C7—C6—H6A	110.8	N1—O1—Cu1	107.35 (8)
C7—C6—H6B	110.8	Cu1—OW1—HW1A	119.7 (15)
C1—C7—C6	105.36 (10)	Cu1—OW1—HW1B	111.5 (15)
C1—C7—H7A	110.7	HW1A—OW1—HW1B	109 (2)
C1—C7—H7B	110.7
C1—C2—C3—C4	−33.81 (15)	C6—C5—N8—C1	−46.59 (12)
C1—C2—C3—N3	93.81 (13)	C6—C5—N8—C8	75.54 (13)
C2—C1—C7—C6	86.42 (13)	C7—C1—C2—C3	−56.77 (15)
C2—C1—N8—C5	−74.06 (12)	C7—C1—N8—C5	47.14 (12)
C2—C1—N8—C8	163.87 (11)	C7—C1—N8—C8	−74.93 (13)
C2—C3—C4—C5	33.45 (15)	N8—C1—C2—C3	55.76 (14)
C3—C4—C5—C6	57.78 (14)	N8—C1—C7—C6	−29.54 (13)
C3—C4—C5—N8	−55.00 (13)	N8—C5—C6—C7	27.56 (13)
C4—C5—C6—C7	−88.46 (13)	N3—C3—C4—C5	−93.28 (13)
C4—C5—N8—C1	73.74 (12)	O2—N1—O1—Cu1	7.68 (14)
C4—C5—N8—C8	−164.13 (11)	O3—N1—O1—Cu1	−173.23 (11)
C5—C6—C7—C1	1.22 (14)

D—H···A	D—H	H···A	D···A	D—H···A
N8—H8···OW1i	0.783 (17)	2.236 (17)	2.9600 (15)	154.0 (15)
OW1—HW1A···Cl1ii	0.79 (2)	2.33 (2)	3.1145 (11)	172.4 (19)
OW1—HW1B···Cl2iii	0.79 (2)	2.30 (2)	3.0851 (11)	179 (2)