Crystal structure of trans-cyclo-hexane-1,2-di-ammonium chromate(VI) from synchrotron X-ray diffraction data.

The structure of the title hybrid compound, (C6H16N2)[CrO4], has been determined from synchrotron data. The organic cation adopts a chair conformation. The inorganic CrO42- anion is slightly distorted owing to its involvement in N-H⋯O hydrogen-bonding inter-actions with neighbouring trans-cyclo-hexane-1,2-di-ammonium cations, whereby the two Cr-O bonds to the O atoms acting as acceptor atoms for two hydrogen bonds are slightly longer than the other two Cr-O bonds for which only one acceptor inter-action per O atom is observed. In the crystal, cations and anions are packed into layers parallel to (001), held together through the aforementioned N-H⋯O hydrogen bonds.

Chemical context

Organic–inorganic hybrid compounds are of inter­est because of the possibility of their forming extended networks through versatile hydrogen bonds (Mkaouar et al., 2016 ▸). The amine trans-1,2-cyclo­hexa­nedi­amine (chxn), C6H14N2, is strongly basic and readily captures two protons to form a dication, (C6H16N2)2+. Crystal structures of this amine or the dication have been determined for trans-1,2-cyclo­hexa­nedi­amine hydro­bromide (Morse & Chesick, 1976 ▸), trans-cyclo­hexane-1,2-di­ammonium dichloride (Farrugia et al., 2001 ▸) and trans-cyclo­hexane-1,2-di­ammonium bis­(3′-nitro-trans-cinnamate) (Hosomi et al., 2000 ▸). With respect to complex inorganic anions of the types ZnCl4 2−, CrO4 2− or Cr2O7 2−, the crystal structures of hybrid compounds with organic ammonium cations have been determined for propane-1,3-di­ammonium tetra­chlorido­zincate (Kallel et al., 1980 ▸), propane-1,3-di­ammonium dichromate(VI) (Trabelsi et al., 2012 ▸) and propane-1,2-di­ammonium chromate(VI) (Trabelsi et al., 2014 ▸). However, a combination of trans-cyclo­hexane-1,2-di­ammonium and CrO4 2− has not been reported. In this communication, we present details on the preparation of the new organic chromate(VI), (C6H16N2)[CrO4], (I) and its structural characterization by synchrotron single-crystal X-ray diffraction.

Structural commentary

Fig. 1 ▸ shows an ellipsoid plot of the mol­ecular components of (I). The organic di­ammonium cation adopts a stable chair conformation with respect to the cyclo­hexane ring. The C—C and N—C distances range from 1.506 (5) to 1.525 (4) Å and from 1.492 (3) to 1.493 (3) Å, respectively; the range of N—C—C and C—C—C angles is 108.3 (2) to 113.7 (2)° and 109.2 (2) to 112.0 (3)°, respectively.

Figure 1

The mol­ecular structures of the organic cation and the inorganic anion in (I), drawn with displacement ellipsoids at the 30% probability level. The dashed line represents a hydrogen-bonding inter­action.

The bond lengths and angles are very similar than in the structure of the bis­(3′-nitro-trans-cinnamate) compound with the same cation (Hosomi et al., 2000 ▸). The cyclo­hexane ring C—C bond lengths and angles and the torsion angles involving the C and N atoms are in essential agreement with the values obtained for [Cr(chxn)3](ZnCl4)Cl·3H2O (Moon & Choi, 2016 ▸). The CrVI atom in the CrO4 2− anion has the characteristic tetra­hedral coordination environment of four O atoms, with Cr—O bond lengths ranging from 1.628 (2) to 1.6654 (19) Å and O—Cr—O angles ranging from 108.30 (10)–111.43 (11)° (Table 1 ▸). The distortion from ideal values is due to the influence of hydrogen bonding. For O atoms that are acceptor atoms of two hydrogen bonds (O1 and O4), the Cr—O bond lengths are slightly longer than those of the other two O atoms (O2 and O3) which are each involved in only one hydrogen-bonding inter­action.

Table 1

Selected geometric parameters (Å, °)

Cr1—O3	1.628 (2)	Cr1—O1	1.6584 (19)
Cr1—O2	1.6394 (19)	Cr1—O4	1.6654 (19)
O3—Cr1—O2	108.60 (11)	O3—Cr1—O4	109.76 (10)
O3—Cr1—O1	111.43 (11)	O2—Cr1—O4	108.30 (10)
O2—Cr1—O1	109.72 (10)	O1—Cr1—O4	108.97 (10)

Supra­molecular features

In the crystal structure, the cations and anions are arranged in layers parallel to (001). The ammonium group is directed towards the anion, hence causing polar and non-polar sections in the crystal structure, alternating along [001]. As mentioned above, each of the O atoms is involved in N—H⋯O hydrogen bonds that hold the polar (001) sheets together (Fig. 2 ▸, Table 2 ▸).

Figure 2

The crystal packing in (I), viewed along [010]. Hydrogen-bonding inter­actions are indicated by dashed lines.

Table 2

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N1⋯O2i	0.91	1.99	2.896 (3)	172
N1—H3N1⋯O1ii	0.91	2.00	2.884 (3)	164
N1—H2N1⋯O4	0.91	1.81	2.713 (3)	175
N2—H1N2⋯O4i	0.91	1.87	2.771 (3)	169
N2—H3N2⋯O2iii	0.91	2.56	3.104 (3)	119
N2—H3N2⋯O3iii	0.91	2.04	2.927 (3)	166
N2—H2N2⋯O1iv	0.91	1.86	2.748 (3)	165

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

Database survey

A search of the Cambridge Structural Database (Version 5.37, Feb 2016 with three updates; Groom et al., 2016 ▸) indicates a total of 31 hits for compounds containing the cyclo­hexa­nedi­ammonium cation (C6H16N2)2+.

Synthesis and crystallization

Compound (I) was prepared by dissolving 5 mmol of chromium trioxide (0.50 g, Sigma–Aldrich) and 0.5 mmol of trans-1,2-cyclo­hexa­nedi­amine (0.6 mL, Sigma-Aldrich) in 40 mL of distilled water with a molar ratio of 1:1. The mixture was stirred for 30 minutes and the resulting solution was allowed to stand at room temperature for one day to give plate-like yellow crystals suitable for X-ray structural analysis.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H = 0.99-1.00 Å and N—H = 0.91 Å, and with U iso(H) values of 1.2 or 1.5U eq of the parent atoms.

Table 3

Experimental details

Crystal data
Chemical formula	(C6H16N2)[CrO4]
M r	232.21
Crystal system, space group	Orthorhombic, P b c a
Temperature (K)	173
a, b, c (Å)	9.910 (2), 8.3730 (17), 22.999 (5)
V (Å3)	1908.4 (7)
Z	8
Radiation type	Synchrotron, λ = 0.650 Å
μ (mm−1)	0.92
Crystal size (mm)	0.10 × 0.09 × 0.01
Data collection
Diffractometer	ADSC Q210 CCD area detector
Absorption correction	Empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997 ▸)
T min, T max	0.794, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	16426, 2383, 1749
R int	0.069
(sin θ/λ)max (Å−1)	0.674
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.055, 0.160, 0.99
No. of reflections	2383
No. of parameters	121
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.95, −1.53

Computer programs: PAL BL2D-SMDC (Shin et al., 2016 ▸), HKL3000sm (Otwinowski & Minor, 1997 ▸), SHELXT2014 (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), DIAMOND (Putz & Brandenburg, 2014 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989016019009/wm5343sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016019009/wm5343Isup2.hkl

CCDC reference: 1519508

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

(C6H16N2)[CrO4]	Dx = 1.616 Mg m−3
Mr = 232.21	Synchrotron radiation, λ = 0.650 Å
Orthorhombic, Pbca	Cell parameters from 49521 reflections
a = 9.910 (2) Å	θ = 0.4–33.4°
b = 8.3730 (17) Å	µ = 0.92 mm−1
c = 22.999 (5) Å	T = 173 K
V = 1908.4 (7) Å3	Plate, yellow
Z = 8	0.10 × 0.09 × 0.01 mm
F(000) = 976

ADSC Q210 CCD area detector diffractometer	1749 reflections with I > 2σ(I)
Radiation source: PLSII 2D bending magnet	Rint = 0.069
ω scan	θmax = 26.0°, θmin = 2.5°
Absorption correction: empirical (using intensity measurements) (HKL3000sm Scalepack; Otwinowski & Minor, 1997)	h = −12→12
Tmin = 0.794, Tmax = 1.000	k = −11→11
16426 measured reflections	l = −31→31
2383 independent reflections

Refinement on F2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F2 > 2σ(F2)] = 0.055	w = 1/[σ2(Fo2) + (0.116P)2] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.160	(Δ/σ)max < 0.001
S = 0.99	Δρmax = 0.95 e Å−3
2383 reflections	Δρmin = −1.53 e Å−3
121 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraints	Extinction coefficient: 0.017 (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
N1	0.6842 (2)	0.3903 (3)	0.43614 (9)	0.0245 (5)
H1N1	0.6673	0.3156	0.4639	0.037*
H2N1	0.6444	0.4842	0.4463	0.037*
H3N1	0.7749	0.4049	0.4328	0.037*
N2	0.4159 (3)	0.2284 (3)	0.42353 (10)	0.0279 (5)
H1N2	0.4273	0.2758	0.4588	0.042*
H2N2	0.4575	0.1315	0.4235	0.042*
H3N2	0.3262	0.2151	0.4165	0.042*
C1	0.6285 (3)	0.3349 (3)	0.37930 (11)	0.0249 (6)
H1	0.6622	0.2241	0.3721	0.030*
C2	0.4758 (3)	0.3313 (3)	0.37730 (12)	0.0247 (5)
H2	0.4413	0.4427	0.3823	0.030*
C3	0.4292 (3)	0.2686 (4)	0.31840 (13)	0.0342 (7)
H3A	0.4600	0.1569	0.3137	0.041*
H3B	0.3293	0.2688	0.3171	0.041*
C4	0.4833 (3)	0.3687 (4)	0.26844 (14)	0.0410 (8)
H4A	0.4570	0.3192	0.2310	0.049*
H4B	0.4430	0.4768	0.2701	0.049*
C5	0.6347 (3)	0.3820 (4)	0.27138 (13)	0.0357 (7)
H5A	0.6665	0.4563	0.2408	0.043*
H5B	0.6754	0.2760	0.2638	0.043*
C6	0.6808 (3)	0.4421 (4)	0.33063 (12)	0.0318 (6)
H6A	0.6475	0.5523	0.3366	0.038*
H6B	0.7807	0.4447	0.3318	0.038*
Cr1	0.44912 (4)	0.79269 (5)	0.43056 (2)	0.0227 (2)
O1	0.53896 (18)	0.9403 (2)	0.40203 (9)	0.0308 (5)
O2	0.34508 (19)	0.8641 (2)	0.47950 (9)	0.0330 (5)
O3	0.3616 (2)	0.6998 (2)	0.38110 (10)	0.0362 (5)
O4	0.55315 (18)	0.6648 (2)	0.46324 (9)	0.0311 (5)

	U11	U22	U33	U12	U13	U23
N1	0.0243 (12)	0.0215 (11)	0.0278 (11)	0.0015 (9)	−0.0012 (8)	0.0002 (8)
N2	0.0267 (13)	0.0252 (12)	0.0316 (13)	0.0024 (10)	0.0025 (9)	0.0012 (9)
C1	0.0249 (14)	0.0217 (12)	0.0279 (13)	0.0026 (10)	0.0002 (10)	−0.0011 (10)
C2	0.0257 (14)	0.0195 (12)	0.0289 (13)	0.0000 (10)	−0.0010 (10)	0.0009 (10)
C3	0.0314 (18)	0.0406 (16)	0.0307 (15)	−0.0072 (12)	−0.0047 (11)	−0.0009 (13)
C4	0.0376 (18)	0.055 (2)	0.0309 (15)	−0.0053 (16)	−0.0050 (12)	0.0073 (14)
C5	0.0317 (16)	0.0437 (17)	0.0315 (15)	−0.0018 (13)	0.0024 (11)	0.0029 (12)
C6	0.0298 (16)	0.0322 (14)	0.0334 (15)	−0.0062 (12)	0.0000 (11)	0.0044 (11)
Cr1	0.0223 (3)	0.0167 (3)	0.0290 (3)	0.00140 (14)	−0.00086 (15)	0.00134 (14)
O1	0.0285 (11)	0.0233 (10)	0.0405 (12)	−0.0002 (8)	0.0062 (8)	0.0049 (8)
O2	0.0305 (11)	0.0285 (10)	0.0402 (11)	0.0053 (8)	0.0078 (9)	0.0010 (8)
O3	0.0349 (12)	0.0293 (11)	0.0444 (13)	0.0026 (8)	−0.0129 (10)	−0.0053 (8)
O4	0.0356 (12)	0.0224 (9)	0.0354 (11)	0.0087 (8)	−0.0053 (8)	0.0010 (8)

N1—C1	1.493 (3)	C3—H3A	0.9900
N1—H1N1	0.9100	C3—H3B	0.9900
N1—H2N1	0.9100	C4—C5	1.506 (5)
N1—H3N1	0.9100	C4—H4A	0.9900
N2—C2	1.492 (3)	C4—H4B	0.9900
N2—H1N2	0.9100	C5—C6	1.523 (4)
N2—H2N2	0.9100	C5—H5A	0.9900
N2—H3N2	0.9100	C5—H5B	0.9900
C1—C2	1.514 (4)	C6—H6A	0.9900
C1—C6	1.525 (4)	C6—H6B	0.9900
C1—H1	1.0000	Cr1—O3	1.628 (2)
C2—C3	1.525 (4)	Cr1—O2	1.6394 (19)
C2—H2	1.0000	Cr1—O1	1.6584 (19)
C3—C4	1.520 (4)	Cr1—O4	1.6654 (19)
C1—N1—H1N1	109.5	C4—C3—H3B	109.2
C1—N1—H2N1	109.5	C2—C3—H3B	109.2
H1N1—N1—H2N1	109.5	H3A—C3—H3B	107.9
C1—N1—H3N1	109.5	C5—C4—C3	111.0 (3)
H1N1—N1—H3N1	109.5	C5—C4—H4A	109.4
H2N1—N1—H3N1	109.5	C3—C4—H4A	109.4
C2—N2—H1N2	109.5	C5—C4—H4B	109.4
C2—N2—H2N2	109.5	C3—C4—H4B	109.4
H1N2—N2—H2N2	109.5	H4A—C4—H4B	108.0
C2—N2—H3N2	109.5	C4—C5—C6	111.3 (2)
H1N2—N2—H3N2	109.5	C4—C5—H5A	109.4
H2N2—N2—H3N2	109.5	C6—C5—H5A	109.4
N1—C1—C2	113.7 (2)	C4—C5—H5B	109.4
N1—C1—C6	109.5 (2)	C6—C5—H5B	109.4
C2—C1—C6	109.2 (2)	H5A—C5—H5B	108.0
N1—C1—H1	108.1	C5—C6—C1	111.1 (2)
C2—C1—H1	108.1	C5—C6—H6A	109.4
C6—C1—H1	108.1	C1—C6—H6A	109.4
N2—C2—C1	112.8 (2)	C5—C6—H6B	109.4
N2—C2—C3	108.3 (2)	C1—C6—H6B	109.4
C1—C2—C3	109.7 (2)	H6A—C6—H6B	108.0
N2—C2—H2	108.7	O3—Cr1—O2	108.60 (11)
C1—C2—H2	108.7	O3—Cr1—O1	111.43 (11)
C3—C2—H2	108.7	O2—Cr1—O1	109.72 (10)
C4—C3—C2	112.0 (3)	O3—Cr1—O4	109.76 (10)
C4—C3—H3A	109.2	O2—Cr1—O4	108.30 (10)
C2—C3—H3A	109.2	O1—Cr1—O4	108.97 (10)
N1—C1—C2—N2	−57.5 (3)	C2—C3—C4—C5	54.6 (4)
C6—C1—C2—N2	179.8 (2)	C3—C4—C5—C6	−53.4 (4)
N1—C1—C2—C3	−178.3 (2)	C4—C5—C6—C1	56.5 (3)
C6—C1—C2—C3	59.0 (3)	N1—C1—C6—C5	175.7 (2)
N2—C2—C3—C4	178.8 (3)	C2—C1—C6—C5	−59.1 (3)
C1—C2—C3—C4	−57.6 (3)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···O2i	0.91	1.99	2.896 (3)	172
N1—H3N1···O1ii	0.91	2.00	2.884 (3)	164
N1—H2N1···O4	0.91	1.81	2.713 (3)	175
N2—H1N2···O4i	0.91	1.87	2.771 (3)	169
N2—H3N2···O2iii	0.91	2.56	3.104 (3)	119
N2—H3N2···O3iii	0.91	2.04	2.927 (3)	166
N2—H2N2···O1iv	0.91	1.86	2.748 (3)	165