Quinolinium dichromate, [C₉H₇NH⁺]₂·Cr₂O₇²⁻

The title compound, (C₉H₈N)₂[Cr₂O₇], crystallizes in the monoclinic space group P2₁/c, with eight cations and four anions in the unit cell. The quinolinium cations and a dichromate anion are connected through N—H...O and C—H...O intermolecular hydrogen bonds and by aromatic π–π-stacking interactions. The dichromate geometry is normal, with a Cr—O(bridging)—Cr angle of 135.1 (2)°.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.008 Å
• R factor = 0.056
• wR factor = 0.162
• Data-to-parameter ratio = 12.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

The X-ray study of quinolinium dichromate (QDC), (I), was undertaken in order to study the hydrogen-bond patterns and crystal packing. QDC is reported to be a selective oxidant for a wide range of substrates in view of its ease of preparation and high stability (Aruna et al., 1994; Aruna & Manikyamba, 1995; Balasubramanian & Prathiba, 1986; Karim & Mahanti, 1992; Kharnaior et al., 2001; Lyngdoh et al., 2001; Ravishankar et al., 1998).

In QDC, two heterocyclic quinolinium cation moieties and a dichromate anion moiety are connected through N—H···O and C—H···O intermolecular hydrogen bonds. The refined asymmetric unit and the numbering scheme are shown in Fig. 1. The aromatic quinolinium moieties form π–π-stacking interactions. One of the six-membered rings, Cg1 (defined by atoms N1, C11–C13, C18 and C19), of the quinolinium moiety at (x, y, z) has a π–π interaction with one of the six-membered rings, Cg4 (defined by atoms C24–C29), at (x, 1/2 − y,-1/2 + z) of another quinolinium moiety. The other six-membered ring, Cg3 (defined by atoms C14–C19), has a π–π contact with Cg2 (defined by atoms N2, C21–C23, C28 and C29) of the quinolinium moiety which belongs to the same asymmetric unit as that of residue (I). The distances between the ring centroids, Cg, are listed in Table 1. The quinolinium rings are stacked along the the c axis, having their planes nearly parallel to the (001) plane (Fig. 2), as is evident from the fact that the dihedral angle between their least-squares planes is 2.87 (9)°. The corresponding bond lengths of the two quinolinium rings are in very good agreement. The largest difference in bond length is observed in the bonds C16—C17 [1.333 (8) Å] and C26—C27 [1.356 (7) Å]. The agreement is also good for the corresponding core angles between the rings, with maximum difference existing between C11—N1—C18 [122.2 (5)°] and C21—N2—C28 [123.3 (4)°]. However, these differences are not significant, as they are well within the 3σ level. Also, the bond distances and angles of the molecule are reasonably comparable with compounds containing the similar quinazoline ring and are in agreement with the related structures (Dobson & Gerkin, 1999a,b; Rajnikant et al., 2002).

The dichromate ion consits of two CrO₄ tetrahedra sharing one O atom (the bridge atom O7). The CrO₄ groups are slightly distorted tetrahedra. The distances of the chromium atoms from the bridging oxygen, O7, are 1.793 (3) (Cr1—O7) and 1.804 (3) Å (Cr2—O7). The other Cr—O distances range from 1.572 (5) (Cr1—O1) to 1.615 (3) Å (Cr2—O6). The dichromate geometry is normal for Cr1—O7—Cr2 [135.1 (2)°]. The angles O3—Cr1—O7 [103.9 (2)°] and O6—Cr2—O7 [103.92 (17)°] significantly differ from the tetrahedral geometry, 109.5°. The similar deviation is described for analogous sulfates in the paper by Brown (1973), where two types of angular distortions occur, known as the bond-length effect and the configurational effect. In the present case, the bond -ength effect is not observed since the O atoms are not in contact, but the configurational effect is observed. There is no significant deviation in the bond angles and distances of the dichromate moiety from the values of similar structures reported in the literature (Panagiotopoulos & Brown, 1972; Dahan, 1975; Blum et al., 1980).

The details of the N—H···O (Fig. 3) and C—H···O (Fig. 4) interactions observed are presented in Table 2. As seen from Table 2, for (I), atoms N1 and N2 act as hydrogen-bond donors and form N—H···O intermolecular interactions with atoms O6 and O7 of the adjacent molecule. H11 on C11 is involved in a weak intermolecular C—H···O interaction with the terminal atom O6 of the adjacent dichromate moiety and H13 on C13 is involved in a weak intermolecular C—H···O interaction with another terminal atom, O3, of another molecule. These interactions produce a continuous chain, which runs parallel to the c axis. Atom C21 forms a weak C—H···O intermolecular interaction with O2 of a neighbouring centrosymmetrically related molecule. Apart from the intermolecular hydrogen bonds, the structure is also stabilized by π–π-stacking interactions (Table 1).

S2. Experimental

QDC was prepared as reported in the literature (Balasubramanian & Prathiba, 1986). To a stirred solution of CrO₃ (10 g) in water (10 ml), cooled in ice, was added quinoline (9 ml), in small portions. The solution was diluted with acetone (40 ml), cooled to 253 K and the orange solid which separated out was filtered off, washed with acetone, dried in vacuo and recrystallized from water (m.p. 433 K, yield 72%).

S3. Refinement

All H atoms were placed in geometrically idealized positions, N—H = 0.86 Å and C—H = 0.93 Å, and constrained to ride on their parent atoms with U_iso(H) = 1.2U_eq(N) and 1.2U_eq(C).

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: WinGX (Version 1.64.02; Farrugia, 1999) and PLATON (Spek, 2002); software used to prepare material for publication: SHELXL97 and PARST (Nardelli, 1995).

Figures

	Fig. 1. The molecular components of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Stereoview of part of the crystal structure of (I), showing the stacking of quinolinium rings along the c axis. Dichromate moieties are omitted for clarity.
	Fig. 3. Part of the crystal structure of (I), showing N—H···O interactions.
	Fig. 4. Part of the crystal structure of (I), showing the formation of a chain through C—H···O interactions. Atoms marked with a hash (#), an asterisk (*), a dollar sign ($) or an ampersand (&) are at the symmetry positions (1 − x, 1 − y, −z), (1 − x, −1/2 + y, −1/2 − z), (x, 1/2 − y, −3/2 + z) and (1 − x, 1/2 + y, −1/2 − z), respectively.

Quinolinium dichromate

Crystal data

(C9H8N)2[Cr2O7]	F(000) = 968
Mr = 476.33	Dx = 1.695 Mg m^−3
Monoclinic, P21/c	Melting point: 433 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 12.286 (5) Å	Cell parameters from 25 reflections
b = 9.965 (3) Å	θ = 2.0–25.0°
c = 15.386 (5) Å	µ = 1.21 mm^−1
β = 97.67 (3)°	T = 293 K
V = 1866.9 (11) Å^3	Needles, orange red
Z = 4	0.30 × 0.20 × 0.10 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	2210 reflections with I > 2σ(I)
Radiation source: Enraf Nonius FR590	Rint = 0.034
Graphite monochromator	θmax = 25.0°, θmin = 2.4°
Non–profiled ω/2θ scans	h = 0→14
Absorption correction: ψ scan (North et al., 1968)	k = 0→11
Tmin = 0.713, Tmax = 0.889	l = −18→18
3447 measured reflections	2 standard reflections every 60 min
3283 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.056	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.162	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0975P)^2 + 1.1704P] where P = (Fo^2 + 2Fc^2)/3
3283 reflections	(Δ/σ)max < 0.001
262 parameters	Δρmax = 1.12 e Å^−3
0 restraints	Δρmin = −0.57 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
N1	0.3239 (4)	0.1135 (4)	0.0009 (3)	0.0541 (11)
H1	0.3304	0.0276	0.0019	0.065*
C11	0.4057 (5)	0.1868 (7)	−0.0208 (4)	0.0615 (15)
H11	0.4691	0.1452	−0.0344	0.074*
C12	0.3977 (5)	0.3259 (7)	−0.0233 (4)	0.0624 (16)
H12	0.4551	0.3771	−0.0393	0.075*
C13	0.3068 (4)	0.3862 (5)	−0.0025 (3)	0.0464 (12)
H13	0.3023	0.4794	−0.0037	0.056*
C14	0.1210 (5)	0.3689 (6)	0.0417 (3)	0.0598 (15)
H14	0.1125	0.4617	0.0412	0.072*
C15	0.0391 (5)	0.2890 (7)	0.0627 (4)	0.0696 (19)
H15	−0.0259	0.3274	0.0756	0.084*
C16	0.0510 (5)	0.1492 (7)	0.0650 (4)	0.0622 (15)
H16	−0.0058	0.0962	0.0804	0.075*
C17	0.1425 (4)	0.0910 (6)	0.0457 (3)	0.0535 (13)
H17	0.1494	−0.0019	0.0479	0.064*
C18	0.2283 (4)	0.1701 (5)	0.0219 (3)	0.0392 (11)
C19	0.2195 (4)	0.3115 (5)	0.0206 (3)	0.0415 (11)
N2	0.3078 (3)	0.0656 (4)	0.2508 (2)	0.0389 (9)
H2	0.3085	−0.0207	0.2510	0.047*
C21	0.3936 (4)	0.1291 (5)	0.2287 (3)	0.0460 (12)
H21	0.4531	0.0806	0.2138	0.055*
C22	0.3959 (5)	0.2692 (5)	0.2273 (4)	0.0514 (13)
H22	0.4563	0.3145	0.2112	0.062*
C23	0.3088 (4)	0.3379 (5)	0.2499 (3)	0.0477 (12)
H23	0.3098	0.4313	0.2491	0.057*
C24	0.1227 (5)	0.3363 (5)	0.2985 (3)	0.0545 (14)
H24	0.1205	0.4295	0.3004	0.065*
C25	0.0368 (5)	0.2649 (6)	0.3188 (4)	0.0586 (15)
H25	−0.0242	0.3094	0.3346	0.070*
C26	0.0379 (4)	0.1243 (6)	0.3163 (3)	0.0536 (13)
H26	−0.0230	0.0765	0.3293	0.064*
C27	0.1267 (4)	0.0572 (5)	0.2951 (3)	0.0465 (12)
H27	0.1276	−0.0361	0.2948	0.056*
C28	0.2174 (4)	0.1298 (4)	0.2737 (3)	0.0350 (10)
C29	0.2170 (4)	0.2711 (4)	0.2743 (3)	0.0375 (10)
Cr1	0.30506 (7)	0.72205 (7)	0.35440 (5)	0.0406 (3)
Cr2	0.31064 (6)	0.73438 (7)	0.13915 (5)	0.0366 (3)
O1	0.1883 (4)	0.6592 (6)	0.3580 (4)	0.1080 (19)
O2	0.3967 (3)	0.6074 (4)	0.3724 (3)	0.0643 (11)
O3	0.3303 (5)	0.8429 (4)	0.4207 (3)	0.1047 (19)
O4	0.1906 (3)	0.6964 (6)	0.0967 (3)	0.0929 (16)
O5	0.3916 (3)	0.6083 (3)	0.1416 (2)	0.0589 (10)
O6	0.3569 (3)	0.8591 (3)	0.0879 (2)	0.0614 (11)
O7	0.3085 (3)	0.7971 (3)	0.2489 (2)	0.0607 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.061 (3)	0.049 (2)	0.051 (3)	0.014 (2)	0.003 (2)	0.000 (2)
C11	0.046 (3)	0.098 (5)	0.041 (3)	0.011 (3)	0.007 (3)	−0.005 (3)
C12	0.058 (4)	0.091 (5)	0.036 (3)	−0.026 (3)	0.002 (3)	0.009 (3)
C13	0.066 (4)	0.041 (3)	0.029 (3)	−0.009 (2)	−0.002 (2)	0.0022 (19)
C14	0.074 (4)	0.063 (3)	0.041 (3)	0.027 (3)	0.001 (3)	−0.012 (3)
C15	0.048 (3)	0.121 (6)	0.041 (3)	0.021 (4)	0.009 (3)	−0.012 (3)
C16	0.054 (4)	0.090 (5)	0.043 (3)	−0.011 (3)	0.009 (3)	0.000 (3)
C17	0.058 (3)	0.057 (3)	0.044 (3)	−0.006 (3)	0.001 (3)	0.003 (2)
C18	0.047 (3)	0.047 (3)	0.023 (2)	0.001 (2)	0.001 (2)	−0.0022 (19)
C19	0.055 (3)	0.042 (2)	0.025 (2)	0.005 (2)	−0.002 (2)	−0.002 (2)
N2	0.052 (2)	0.0322 (19)	0.033 (2)	0.0054 (18)	0.0047 (18)	−0.0024 (15)
C21	0.045 (3)	0.055 (3)	0.038 (3)	0.004 (2)	0.005 (2)	−0.003 (2)
C22	0.049 (3)	0.060 (3)	0.046 (3)	−0.017 (3)	0.010 (2)	0.001 (2)
C23	0.070 (4)	0.032 (2)	0.039 (3)	−0.009 (2)	0.001 (2)	−0.0002 (19)
C24	0.076 (4)	0.044 (3)	0.043 (3)	0.016 (3)	0.005 (3)	−0.003 (2)
C25	0.053 (3)	0.081 (4)	0.044 (3)	0.017 (3)	0.014 (3)	0.002 (3)
C26	0.047 (3)	0.077 (4)	0.037 (3)	−0.002 (3)	0.009 (2)	0.010 (3)
C27	0.053 (3)	0.045 (3)	0.041 (3)	−0.009 (2)	0.005 (2)	0.005 (2)
C28	0.045 (3)	0.039 (2)	0.021 (2)	0.0022 (19)	0.0021 (19)	−0.0004 (17)
C29	0.048 (3)	0.038 (2)	0.024 (2)	0.001 (2)	−0.0012 (19)	−0.0030 (18)
Cr1	0.0604 (6)	0.0343 (4)	0.0298 (4)	0.0023 (3)	0.0166 (4)	0.0007 (3)
Cr2	0.0472 (5)	0.0370 (4)	0.0269 (4)	−0.0002 (3)	0.0089 (3)	−0.0026 (3)
O1	0.068 (3)	0.117 (4)	0.146 (5)	−0.004 (3)	0.043 (3)	0.022 (4)
O2	0.078 (3)	0.058 (2)	0.059 (3)	0.0172 (19)	0.012 (2)	0.0113 (19)
O3	0.227 (6)	0.046 (2)	0.038 (2)	0.013 (3)	0.009 (3)	−0.0123 (18)
O4	0.056 (3)	0.138 (4)	0.087 (4)	−0.022 (3)	0.015 (2)	−0.021 (3)
O5	0.091 (3)	0.0390 (18)	0.049 (2)	0.0136 (18)	0.016 (2)	−0.0014 (16)
O6	0.096 (3)	0.0411 (18)	0.052 (2)	0.0033 (19)	0.028 (2)	0.0077 (16)
O7	0.113 (3)	0.0398 (19)	0.032 (2)	0.0141 (19)	0.022 (2)	0.0001 (14)

Geometric parameters (Å, º)

N1—C11	1.321 (7)	C22—C23	1.355 (7)
N1—C18	1.380 (6)	C22—H22	0.9300
N1—H1	0.8600	C23—C29	1.403 (7)
C11—C12	1.389 (9)	C23—H23	0.9300
C11—H11	0.9300	C24—C25	1.343 (8)
C12—C13	1.344 (8)	C24—C29	1.421 (7)
C12—H12	0.9300	C24—H24	0.9300
C13—C19	1.391 (7)	C25—C26	1.402 (8)
C13—H13	0.9300	C25—H25	0.9300
C14—C15	1.356 (8)	C26—C27	1.356 (7)
C14—C19	1.415 (7)	C26—H26	0.9300
C14—H14	0.9300	C27—C28	1.404 (6)
C15—C16	1.401 (9)	C27—H27	0.9300
C15—H15	0.9300	C28—C29	1.408 (6)
C16—C17	1.333 (8)	Cr1—O1	1.572 (5)
C16—H16	0.9300	Cr1—O3	1.582 (4)
C17—C18	1.404 (7)	Cr1—O2	1.602 (4)
C17—H17	0.9300	Cr1—O7	1.793 (3)
C18—C19	1.414 (7)	Cr2—O4	1.577 (4)
N2—C21	1.312 (6)	Cr2—O5	1.599 (3)
N2—C28	1.368 (6)	Cr2—O6	1.615 (3)
N2—H2	0.8600	Cr2—O7	1.804 (3)
C21—C22	1.397 (7)	Cg1—Cg4	3.667 (3)
C21—H21	0.9300	Cg2—Cg3	3.609 (3)
C11—N1—C18	122.2 (5)	C23—C22—H22	120.6
C11—N1—H1	118.9	C21—C22—H22	120.6
C18—N1—H1	118.9	C22—C23—C29	121.3 (4)
N1—C11—C12	120.4 (5)	C22—C23—H23	119.4
N1—C11—H11	119.8	C29—C23—H23	119.4
C12—C11—H11	119.8	C25—C24—C29	120.9 (5)
C13—C12—C11	119.8 (5)	C25—C24—H24	119.6
C13—C12—H12	120.1	C29—C24—H24	119.6
C11—C12—H12	120.1	C24—C25—C26	120.8 (5)
C12—C13—C19	121.0 (5)	C24—C25—H25	119.6
C12—C13—H13	119.5	C26—C25—H25	119.6
C19—C13—H13	119.5	C27—C26—C25	120.7 (5)
C15—C14—C19	120.1 (5)	C27—C26—H26	119.7
C15—C14—H14	119.9	C25—C26—H26	119.7
C19—C14—H14	119.9	C26—C27—C28	119.5 (5)
C14—C15—C16	120.8 (5)	C26—C27—H27	120.3
C14—C15—H15	119.6	C28—C27—H27	120.3
C16—C15—H15	119.6	N2—C28—C27	121.1 (4)
C17—C16—C15	121.0 (6)	N2—C28—C29	118.2 (4)
C17—C16—H16	119.5	C27—C28—C29	120.7 (4)
C15—C16—H16	119.5	C23—C29—C28	118.0 (4)
C16—C17—C18	119.9 (5)	C23—C29—C24	124.5 (5)
C16—C17—H17	120.0	C28—C29—C24	117.5 (4)
C18—C17—H17	120.0	O1—Cr1—O3	112.4 (3)
N1—C18—C17	121.6 (4)	O1—Cr1—O2	109.5 (3)
N1—C18—C19	118.1 (4)	O3—Cr1—O2	111.0 (3)
C17—C18—C19	120.3 (5)	O1—Cr1—O7	109.2 (3)
C13—C19—C18	118.5 (5)	O3—Cr1—O7	103.9 (2)
C13—C19—C14	123.7 (5)	O2—Cr1—O7	110.62 (18)
C18—C19—C14	117.8 (5)	O4—Cr2—O5	111.4 (3)
C21—N2—C28	123.3 (4)	O4—Cr2—O6	110.7 (3)
C21—N2—H2	118.4	O5—Cr2—O6	110.95 (19)
C28—N2—H2	118.4	O4—Cr2—O7	110.0 (2)
N2—C21—C22	120.3 (5)	O5—Cr2—O7	109.66 (18)
N2—C21—H21	119.8	O6—Cr2—O7	103.92 (17)
C22—C21—H21	119.8	Cr1—O7—Cr2	135.1 (2)
C23—C22—C21	118.9 (5)
C18—N1—C11—C12	−0.2 (8)	C29—C24—C25—C26	−0.1 (8)
N1—C11—C12—C13	0.9 (9)	C24—C25—C26—C27	1.4 (9)
C11—C12—C13—C19	−0.8 (8)	C25—C26—C27—C28	−1.4 (8)
C19—C14—C15—C16	1.0 (8)	C21—N2—C28—C27	178.6 (4)
C14—C15—C16—C17	−0.9 (9)	C21—N2—C28—C29	−0.7 (6)
C15—C16—C17—C18	−0.4 (9)	C26—C27—C28—N2	−179.1 (4)
C11—N1—C18—C17	−179.3 (5)	C26—C27—C28—C29	0.2 (7)
C11—N1—C18—C19	−0.5 (7)	C22—C23—C29—C28	−0.8 (7)
C16—C17—C18—N1	−179.6 (5)	C22—C23—C29—C24	−179.9 (5)
C16—C17—C18—C19	1.7 (8)	N2—C28—C29—C23	1.1 (6)
C12—C13—C19—C18	0.1 (7)	C27—C28—C29—C23	−178.2 (4)
C12—C13—C19—C14	−178.9 (5)	N2—C28—C29—C24	−179.7 (4)
N1—C18—C19—C13	0.6 (7)	C27—C28—C29—C24	1.0 (7)
C17—C18—C19—C13	179.4 (4)	C25—C24—C29—C23	178.1 (5)
N1—C18—C19—C14	179.6 (4)	C25—C24—C29—C28	−1.0 (7)
C17—C18—C19—C14	−1.6 (7)	O1—Cr1—O7—Cr2	−71.5 (4)
C15—C14—C19—C13	179.3 (5)	O3—Cr1—O7—Cr2	168.3 (4)
C15—C14—C19—C18	0.3 (7)	O2—Cr1—O7—Cr2	49.1 (4)
C28—N2—C21—C22	−0.1 (7)	O4—Cr2—O7—Cr1	81.3 (4)
N2—C21—C22—C23	0.5 (8)	O5—Cr2—O7—Cr1	−41.6 (4)
C21—C22—C23—C29	0.0 (8)	O6—Cr2—O7—Cr1	−160.3 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O6^i	0.86	2.14	2.871 (5)	143
N2—H2···O7^i	0.86	1.82	2.676 (5)	179
C11—H11···O6^ii	0.93	2.39	3.254 (7)	154
C13—H13···O3^iii	0.93	2.17	2.976 (6)	144
C21—H21···O2^iv	0.93	2.43	3.189 (6)	139
C24—H24···O1	0.93	2.55	3.413 (8)	154

Symmetry codes: (i) x, y−1, z; (ii) −x+1, −y+1, −z; (iii) x, −y+3/2, z−1/2; (iv) −x+1, y−1/2, −z+1/2.