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The title compound, (C6H14N2)[Cr2O7], consists of a di­aza­bi­cyclo­[2.2.2]­octane-1,4-diium cation and a discrete dichromate anion, which are linked in the crystal by N—H...O hydrogen bonds. The cation is ordered and distorted, owing to the confinement and twist of the hydrogen bonds involved. Two CrO4 tetrahedra are joined through a shared O atom to form the dichromate anion. Chiral supramolecular chains of the title compound are built up via N—H...O hydrogen bonds, and C—H...O interactions play subordinate roles in forming the structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010402342X/na1676sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010402342X/na1676Isup2.hkl
Contains datablock I

CCDC reference: 256991

Comment top

Chromates may exist as mono-, di-, tri-, tetra- and poly-forms (Pressprich et al., 1988; Wang et al., 2003; Yim & Nam, 2004; Fouada et al., 1999). As no theory can currently predict the real state of these chromium compounds, many experimental attempts to find new chromates have been made since the turn of the century. We have now synthesized the title salt, (I), and its structure is here compared with those of other chromates. \sch

Fig. 1 shows the asymmetric unit of the counter-balanced ion pair of (I), consisting of a diprotonated diazabicyclo[2.2.2]octane (DABCO) cation and a discrete dichromate anion, linked via an N1—H1···O2 hydrogen bond (Table 2). The dichromate anion is composed of two CrO4 tetrahedra joined through a shared O atom. The bridging Cr—O bond lengths, Cr1—O4 and Cr2—O4, are longer than the terminal Cr—O bonds. The O—Cr—O angles range from 106.82 (10) to 111.68 (11)°. Therefore, the coordination geometries formed by the four O atoms around each Cr atom are distorted tetrahedra. The bond lengths and angles are in good agreement with those found in bipyridinium dichromates (Martín-Zarza et al., 1995), bis(octyltrimethylammonium) dichromate (Fossé et al., 1998) and tetramethylammonium dichromate (Fossé et al., 2001). (CrO3)n is an extreme case of a polychromate, where chains of corner-sharing CrO4 tetrahedra are extended along the whole crystal (Stephens & Cruickshank, 1970). In (I), the bridging Cr—O bond distance is obviously longer than that in (CrO3)n (1.748 Å), and the terminal Cr—O distances are comparable with those of (CrO3)n (1.599 Å).

Compound (I) demonstrates a hydrogen-bonding network of N—H···O and C—H···O interactions, which is similar to what is observed in diprotonated DABCO trichromate (Ding et al., 2004). There are bifurcated hydrogen bonds between the cations and the anions, namely N1—H1···O2 and N1—H1···O1i, and N2—H2···O7ii and N2—H2···O5iii (Table 2). With careful study, two chiral supramolecular chains of (I) are observed, which could be described in graph-set notation (Etter, 1990) as C22(11). One chain is formed via N1—H1···O2 and N2—H2···O7ii interactions and runs along the c axis (Fig. 3), and another is formed via N1—H1···O2 and N2—H2···O5iii interactions and runs along the b axis (Fig. 2). These chains are joined by a number of C—H···O interactions, of which the shortest is C1—H1A···O1i (Table 2). Hydrogen-bonded chains are formed in (I), rather than the hydrogen-bonded rings observed in diprotonated DABCO trichromate.

DABCO may assume one of several conformations, namely ordered and non-distorted, ordered and distorted, disordered and non-distorted, or disordered and distorted (Nimmo & Lucas, 1976). Disordered conformations are frequently observed, such as 1:1 DABCO-biphenol (Ferguson et al., 1998), 1:1 DABCO-perchloric acid (Katrusiak, 2000) and 1:2 DABCO-maleic acid (Sun & Jin, 2002). In (I), the diprotonated DABCO is ordered and distorted, owing to the confinement and twist of the above-mentioned hydrogen bonds. The situation is similar to that in diprotonated DABCO trichromate. In (I), the N—C—C—N torsion angles, with a mean value of 17.1 (3)°, indicate such a great distortion as to be comparable with the motif in an encapsuled diprotonated DABCO (Jin et al., 2003).

Experimental top

CrO3 (0.2 mol) and DABCO (0.1 mol) were dissolved separately in adequate H2O (1.5 and 1.2 mol), and the two solutions were then mixed with cautious stirring. Crystals of the title salt were formed in the final solution by slow evaporation of water at 298 K for a week.

Refinement top

The H atoms of the NH groups were located in difference Fourier maps and refined with the N—H distance restrained. All remaining H atoms were placed in calculated positions and allowed to ride on their parent atoms, with C—H = 0.97 Å and with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level and H atoms are shown as small spheres of arbitrary radii. The dashed line indicates one of the hydrogen bonds.
[Figure 2] Fig. 2. The chiral supramolecular C22(11) chain of (I), which is formed via N—H···O hydrogen bonds (indicated by dashed lines), viewed along the b axis. The atom labelled with a hash (#) is at the symmetry position (1 − x, y − 1/2, 1/2 − z).
[Figure 3] Fig. 3. The chiral supramolecular C22(11) chain of (I), which is formed via N—H···O hydrogen bonds (indicated by dotted lines), viewed along the c axis. The atom labelled with an asterisk (*) is at the symmetry position (x, 3/2 − y, z + 1/2).
Diazabicyclo[2.2.2]octane-1,4-diium dichromate top
Crystal data top
(C6H14N2)[Cr2O7]F(000) = 1344
Mr = 330.19Dx = 1.965 Mg m3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P2ac2abCell parameters from 5621 reflections
a = 9.0727 (4) Åθ = 2.9–25.2°
b = 12.9327 (5) ŵ = 1.97 mm1
c = 19.0201 (8) ÅT = 298 K
V = 2231.71 (16) Å3Block, red
Z = 80.34 × 0.27 × 0.23 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer
2005 independent reflections
Radiation source: fine-focus sealed tube1889 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.026
ϕ and ω scansθmax = 25.2°, θmin = 2.1°
Absorption correction: integration
(SADABS; Bruker, 2000)
h = 1010
Tmin = 0.554, Tmax = 0.660k = 1415
10994 measured reflectionsl = 1922
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.029H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.081 w = 1/[σ2(Fo2) + (0.0435P)2 + 2.1654P]
where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max < 0.001
2005 reflectionsΔρmax = 0.36 e Å3
163 parametersΔρmin = 0.28 e Å3
2 restraintsExtinction correction: SHELXTL (Bruker, 2000), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0075 (5)
Crystal data top
(C6H14N2)[Cr2O7]V = 2231.71 (16) Å3
Mr = 330.19Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 9.0727 (4) ŵ = 1.97 mm1
b = 12.9327 (5) ÅT = 298 K
c = 19.0201 (8) Å0.34 × 0.27 × 0.23 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer
2005 independent reflections
Absorption correction: integration
(SADABS; Bruker, 2000)
1889 reflections with I > 2σ(I)
Tmin = 0.554, Tmax = 0.660Rint = 0.026
10994 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0292 restraints
wR(F2) = 0.081H atoms treated by a mixture of independent and constrained refinement
S = 1.09Δρmax = 0.36 e Å3
2005 reflectionsΔρmin = 0.28 e Å3
163 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
H20.257 (3)0.590 (2)0.4315 (15)0.045 (9)*
H10.016 (3)0.8291 (18)0.3269 (14)0.039 (8)*
Cr10.14305 (4)0.92266 (3)0.17742 (2)0.02208 (16)
Cr20.35354 (4)1.05206 (3)0.08222 (2)0.02211 (16)
O10.2633 (2)0.83204 (14)0.18856 (11)0.0396 (5)
O20.0521 (2)0.94089 (14)0.24937 (10)0.0383 (5)
O30.0291 (2)0.89510 (16)0.11518 (10)0.0406 (5)
O40.23041 (19)1.04206 (12)0.15559 (9)0.0267 (4)
O50.5154 (2)1.01342 (17)0.10452 (12)0.0463 (5)
O60.3606 (2)1.17191 (17)0.06117 (13)0.0489 (6)
O70.2893 (3)0.9839 (3)0.01921 (12)0.0780 (10)
N10.0684 (2)0.77568 (15)0.34751 (11)0.0239 (4)
N20.2060 (2)0.63563 (15)0.40841 (11)0.0242 (4)
C10.0115 (3)0.7470 (2)0.41333 (13)0.0283 (5)
H1A0.11490.73530.40330.034*
H1B0.00390.80250.44750.034*
C20.0580 (3)0.64893 (19)0.44250 (13)0.0278 (5)
H2A0.06920.65440.49310.033*
H2B0.00420.58980.43230.033*
C30.2916 (3)0.73390 (19)0.41383 (14)0.0288 (6)
H3A0.39310.72230.39990.035*
H3B0.29090.75870.46200.035*
C40.2202 (3)0.81354 (18)0.36553 (14)0.0270 (5)
H4A0.21440.88000.38900.032*
H4B0.27840.82170.32310.032*
C50.0776 (3)0.68334 (19)0.30018 (13)0.0290 (6)
H5A0.11100.70400.25380.035*
H5B0.01860.65140.29560.035*
C60.1870 (3)0.6069 (2)0.33281 (14)0.0303 (6)
H6A0.14950.53690.32900.036*
H6B0.28080.61050.30850.036*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cr10.0227 (2)0.0211 (2)0.0225 (2)0.00086 (14)0.00592 (15)0.00310 (15)
Cr20.0207 (2)0.0244 (2)0.0212 (2)0.00480 (14)0.00231 (15)0.00068 (15)
O10.0381 (11)0.0329 (10)0.0476 (11)0.0124 (9)0.0126 (9)0.0072 (8)
O20.0438 (12)0.0384 (10)0.0329 (10)0.0126 (9)0.0174 (9)0.0112 (8)
O30.0372 (11)0.0451 (11)0.0396 (11)0.0148 (9)0.0025 (9)0.0012 (9)
O40.0316 (10)0.0227 (8)0.0258 (9)0.0031 (7)0.0068 (7)0.0019 (7)
O50.0296 (11)0.0532 (13)0.0560 (13)0.0111 (9)0.0076 (10)0.0155 (11)
O60.0433 (13)0.0390 (12)0.0645 (15)0.0057 (9)0.0153 (10)0.0225 (11)
O70.0651 (17)0.125 (2)0.0438 (13)0.0595 (17)0.0214 (12)0.0443 (15)
N10.0215 (10)0.0227 (10)0.0275 (10)0.0022 (8)0.0039 (8)0.0071 (8)
N20.0227 (11)0.0197 (10)0.0300 (11)0.0036 (8)0.0062 (8)0.0050 (8)
C10.0202 (12)0.0346 (13)0.0299 (13)0.0041 (10)0.0043 (10)0.0043 (11)
C20.0273 (13)0.0321 (13)0.0241 (12)0.0029 (10)0.0006 (10)0.0085 (10)
C30.0198 (13)0.0284 (13)0.0382 (14)0.0028 (10)0.0088 (10)0.0002 (11)
C40.0229 (12)0.0221 (12)0.0361 (14)0.0046 (9)0.0014 (11)0.0030 (10)
C50.0339 (14)0.0308 (13)0.0222 (12)0.0060 (11)0.0056 (10)0.0017 (10)
C60.0321 (14)0.0260 (12)0.0328 (14)0.0021 (11)0.0006 (11)0.0039 (11)
Geometric parameters (Å, º) top
Cr1—O31.612 (2)C1—C21.521 (3)
Cr1—O21.6153 (18)C1—H1A0.9700
Cr1—O11.6153 (18)C1—H1B0.9700
Cr1—O41.7847 (16)C2—H2A0.9700
Cr2—O71.598 (2)C2—H2B0.9700
Cr2—O61.602 (2)C3—C41.524 (3)
Cr2—O51.608 (2)C3—H3A0.9700
Cr2—O41.7921 (17)C3—H3B0.9700
N1—C11.493 (3)C4—H4A0.9700
N1—C51.498 (3)C4—H4B0.9700
N1—C41.502 (3)C5—C61.532 (4)
N1—H10.926 (17)C5—H5A0.9700
N2—C31.493 (3)C5—H5B0.9700
N2—C61.495 (3)C6—H6A0.9700
N2—C21.501 (3)C6—H6B0.9700
N2—H20.867 (18)
O3—Cr1—O2109.08 (11)N2—C2—C1107.98 (18)
O3—Cr1—O1111.68 (11)N2—C2—H2A110.1
O2—Cr1—O1109.87 (10)C1—C2—H2A110.1
O3—Cr1—O4107.78 (9)N2—C2—H2B110.1
O2—Cr1—O4107.32 (9)C1—C2—H2B110.1
O1—Cr1—O4110.99 (9)H2A—C2—H2B108.4
O7—Cr2—O6111.16 (16)N2—C3—C4108.23 (18)
O7—Cr2—O5111.05 (15)N2—C3—H3A110.1
O6—Cr2—O5109.28 (11)C4—C3—H3A110.1
O7—Cr2—O4108.46 (10)N2—C3—H3B110.1
O6—Cr2—O4106.82 (10)C4—C3—H3B110.1
O5—Cr2—O4109.97 (10)H3A—C3—H3B108.4
Cr1—O4—Cr2121.36 (9)N1—C4—C3107.86 (18)
C1—N1—C5109.44 (19)N1—C4—H4A110.1
C1—N1—C4109.56 (19)C3—C4—H4A110.1
C5—N1—C4110.23 (19)N1—C4—H4B110.1
C1—N1—H1107.0 (19)C3—C4—H4B110.1
C5—N1—H1111.7 (18)H4A—C4—H4B108.4
C4—N1—H1108.9 (19)N1—C5—C6107.90 (19)
C3—N2—C6109.75 (19)N1—C5—H5A110.1
C3—N2—C2109.75 (18)C6—C5—H5A110.1
C6—N2—C2109.93 (19)N1—C5—H5B110.1
C3—N2—H2105 (2)C6—C5—H5B110.1
C6—N2—H2112 (2)H5A—C5—H5B108.4
C2—N2—H2110 (2)N2—C6—C5107.67 (19)
N1—C1—C2108.18 (19)N2—C6—H6A110.2
N1—C1—H1A110.1C5—C6—H6A110.2
C2—C1—H1A110.1N2—C6—H6B110.2
N1—C1—H1B110.1C5—C6—H6B110.2
C2—C1—H1B110.1H6A—C6—H6B108.5
H1A—C1—H1B108.4
O3—Cr1—O4—Cr267.22 (14)C6—N2—C3—C450.7 (3)
O2—Cr1—O4—Cr2175.43 (11)C2—N2—C3—C470.2 (2)
O1—Cr1—O4—Cr255.37 (14)C1—N1—C4—C350.5 (3)
O7—Cr2—O4—Cr138.95 (18)C5—N1—C4—C369.9 (2)
O6—Cr2—O4—Cr1158.86 (13)N2—C3—C4—N116.6 (3)
O5—Cr2—O4—Cr182.67 (14)C1—N1—C5—C671.3 (2)
C5—N1—C1—C250.3 (3)C4—N1—C5—C649.3 (2)
C4—N1—C1—C270.7 (2)C3—N2—C6—C571.3 (2)
C3—N2—C2—C150.2 (3)C2—N2—C6—C549.5 (2)
C6—N2—C2—C170.6 (2)N1—C5—C6—N217.8 (3)
N1—C1—C2—N217.0 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O20.93 (2)2.09 (2)2.841 (3)137
N1—H1···O1i0.93 (2)2.31 (3)2.943 (3)125
N2—H2···O7ii0.87 (2)1.95 (3)2.720 (3)148
N2—H2···O5iii0.87 (2)2.39 (3)2.992 (3)127
C1—H1A···O1i0.972.423.023 (3)120
C1—H1A···O6iv0.972.473.348 (3)151
C1—H1B···O6v0.972.553.299 (3)135
C2—H2A···O3ii0.972.443.344 (3)156
C3—H3A···O3vi0.972.573.049 (3)111
C3—H3A···O6iii0.972.443.291 (3)146
C3—H3B···O6v0.972.503.353 (4)147
C4—H4A···O5i0.972.503.234 (3)132
C4—H4B···O10.972.573.397 (3)144
C5—H5A···O10.972.493.323 (3)144
C5—H5B···O4iv0.972.563.443 (3)151
Symmetry codes: (i) x1/2, y, z+1/2; (ii) x, y+3/2, z+1/2; (iii) x+1, y1/2, z+1/2; (iv) x, y1/2, z+1/2; (v) x+1/2, y+2, z+1/2; (vi) x+1/2, y, z+1/2.

Experimental details

Crystal data
Chemical formula(C6H14N2)[Cr2O7]
Mr330.19
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)298
a, b, c (Å)9.0727 (4), 12.9327 (5), 19.0201 (8)
V3)2231.71 (16)
Z8
Radiation typeMo Kα
µ (mm1)1.97
Crystal size (mm)0.34 × 0.27 × 0.23
Data collection
DiffractometerBruker SMART CCD area-detector
diffractometer
Absorption correctionIntegration
(SADABS; Bruker, 2000)
Tmin, Tmax0.554, 0.660
No. of measured, independent and
observed [I > 2σ(I)] reflections
10994, 2005, 1889
Rint0.026
(sin θ/λ)max1)0.599
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.029, 0.081, 1.09
No. of reflections2005
No. of parameters163
No. of restraints2
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.36, 0.28

Computer programs: SMART (Bruker, 2000), SMART, SAINT (Bruker, 2000), SHELXTL (Bruker, 2000), SHELXTL.

Selected geometric parameters (Å, º) top
Cr1—O31.612 (2)N1—C51.498 (3)
Cr1—O21.6153 (18)N1—C41.502 (3)
Cr1—O11.6153 (18)N2—C31.493 (3)
Cr1—O41.7847 (16)N2—C61.495 (3)
Cr2—O71.598 (2)N2—C21.501 (3)
Cr2—O61.602 (2)C1—C21.521 (3)
Cr2—O51.608 (2)C3—C41.524 (3)
Cr2—O41.7921 (17)C5—C61.532 (4)
N1—C11.493 (3)
O3—Cr1—O2109.08 (11)O7—Cr2—O5111.05 (15)
O3—Cr1—O1111.68 (11)O6—Cr2—O5109.28 (11)
O2—Cr1—O1109.87 (10)O7—Cr2—O4108.46 (10)
O3—Cr1—O4107.78 (9)O6—Cr2—O4106.82 (10)
O2—Cr1—O4107.32 (9)O5—Cr2—O4109.97 (10)
O1—Cr1—O4110.99 (9)Cr1—O4—Cr2121.36 (9)
O7—Cr2—O6111.16 (16)
N1—C1—C2—N217.0 (3)N1—C5—C6—N217.8 (3)
N2—C3—C4—N116.6 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O20.926 (17)2.09 (2)2.841 (3)137
N1—H1···O1i0.926 (17)2.31 (3)2.943 (3)125
N2—H2···O7ii0.867 (18)1.95 (3)2.720 (3)148
N2—H2···O5iii0.867 (18)2.39 (3)2.992 (3)127
C1—H1A···O1i0.972.423.023 (3)120
C1—H1A···O6iv0.972.473.348 (3)151
C1—H1B···O6v0.972.553.299 (3)135
C2—H2A···O3ii0.972.443.344 (3)156
C3—H3A···O3vi0.972.573.049 (3)111
C3—H3A···O6iii0.972.443.291 (3)146
C3—H3B···O6v0.972.503.353 (4)147
C4—H4A···O5i0.972.503.234 (3)132
C4—H4B···O10.972.573.397 (3)144
C5—H5A···O10.972.493.323 (3)144
C5—H5B···O4iv0.972.563.443 (3)151
Symmetry codes: (i) x1/2, y, z+1/2; (ii) x, y+3/2, z+1/2; (iii) x+1, y1/2, z+1/2; (iv) x, y1/2, z+1/2; (v) x+1/2, y+2, z+1/2; (vi) x+1/2, y, z+1/2.
 

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