Bis(ethyl­enediammonium) dichromate oxalate

The structure of the title compound, [NH₃(CH₂)₂NH₃]₂[Cr₂O₇](C₂O₄), consists of inorganic columns of dichromate anions running along the c axis and organic layers of formula {[(C₂H₁₀N₂)₂·C₂O₄]_n}²ⁿ⁺ parallel to the (100) plane. The dichromate anion lies on a crystallographic twofold rotation axis and the oxalate anion on a centre of symmetry. Three of the four crystallographically independent O atoms of the dichromate anion are disordered, two over two sites and one over three sites; the site occupancy factors are approximately 0.65:0.35, 0.7:0.3 and 0.4:0.3:0.3. Structural cohesion is ensured by N—H...O hydrogen-bonding inter­actions, which form a three-dimensional framework.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• Disorder in main residue
• R factor = 0.041
• wR factor = 0.124
• Data-to-parameter ratio = 12.9

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT241_ALERT_2_B Check High      Ueq as Compared to Neighbors for         O4
PLAT369_ALERT_2_B Long   C(sp2)-C(sp2) Bond  C1     -   C1_b   ...       1.57 Ang.

Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         Cr
PLAT301_ALERT_3_C Main Residue  Disorder .........................      20.00 Perc.
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.38 Ratio
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          2
              C2 H10 N2

Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......         15

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Our recent investigations on organic chromates have led to the synthesis of several compounds using slow solvent evaporation at room temperature (Khadhrani, Ben Smail & Driss, 2006; Khadhrani, Ben Smaïl, Driss & Jouini, 2006; Chebbi & Driss, 2001, 2002a, 2002b, 2004; Chebbi et al., 2000; Chebbi et al., 2003) These materials result from the interaction between aqueous solutions of chromium(VI) oxide and organic molecules having at least one lone pair of electrons, such as amines and aminoalcohols. These structures have been characterized by single-crystal X-ray diffraction. All the synthesized complexes exhibit three-dimensional framework structures, structural cohesion being established by various kinds of hydrogen bonds. As a continuation of this work, we describe here the synthesis and crystal structure of a new organic oxalate dichromate [NH₃(CH₂)₂NH₃]₂[C₂O₄][Cr₂O₇], (I).

The asymmetric unit of (I) contains one ethylenediammonium cation, half a dichromate anion and half an oxalate anion (Fig. 1). The crystal packing generates inorganic columns consisting of dichromate anions stacked along the z axis and organic layers of formula [(C₂H₁₀N₂)₂·C₂O₄]_n²ⁿ⁺ parallel to (100) plane, formed by ethylenediammonium and oxalate ions linked by N—H···O(oxalate) hydrogen bonds (Fig. 2). There are two organic layers per unit cell at x=1/4 and x =3/4, while the inorganic groups provide the cohesion among the layers through N—H···O(dichromate) hydrogen bonds. All hydrogen bonds in the structure (Table 1) are week (Brown, 1976; Blessing, 1986).

The N—C and C—C bond lengths and the C—C—N angles within the cation are comparable with those observed for [NH₃-(CH₂)-NH₃] [Cr₂O₇] (Lorenzo-Luis et al., 1995; Srinivasan et al., 2003) and [NH₃-(CH₂)-NH₃][CrO₄] (Chebbi & Driss, 2004; Srinivasan et al., 2003).

The oxalate ion is centrosymmetric. The C—C and C—O distances are in good agreement with those observed in the unique organic oxalate dichromate published (Khadhrani, Ben Smail & Driss, 2006).

The dichromate anion possesses a twofold symmetry axis passing through atom O3. The Cr—O terminal bond lengths are in the range 1.538 (4)–1.712 (8) Å and the bridging Cr—O bonds are longer and in the range 1.760 (7)–1.810 (8) Å. These values are in good agreement with those usually found in organic dichromates (Fossé & Brohan, 1999; Fossé et al., 1998; Fossé et al., 2001). Atoms O2 and O4 of the dichromate anion are disordered over two positions separeted by 1.351 (10) and 1.201 (12) Å, respectively. Atom O3 is disordered over three positions, two of which generated by the twofold rotation axis, separated by 0.935 (9) Å. This type of disorder has also been observed in the crystal structure of bis-dihexadecyldimethylammonium dichromate (Fossé & Brohan, 1999) and (Hdpam)₂Cr₂O₇ (Martin-Zarza et al., 1995).

Related literature

For general background, see: Khadhrani, Ben Smail & Driss (2006); Khadhrani, Ben Smaïl, Driss & Jouini (2006); Chebbi & Driss (2001, 2002a,b); Chebbi et al. (2000, 2003). For related structures, see: Chebbi & Driss (2004); Fossé & Brohan (1999); Fossé et al. (1998, 2001); Lorenzo-Luis et al. (1995); Martin-Zarza et al. (1995); Srinivasan et al. (2003). For related literature, see: Blessing (1986); Brown (1976).

S2. Experimental

To a solution of CrO₃ (3.2 g) and (NH₄)₂C₂O₄ (1.2 g) in water (50 ml) C₂N₂H₈ (1 ml) was added under stirring. The reaction mixture was allowed to stand for a week at room temperature. Orange-red single crystals, suitable of X-ray analysis, were isolated on slow evaporation of the solvent. The presence of Cr, O, C, anc N was confirmed by EDS (energy dispersive spectroscopy) on a scanning electron microscope.

S3. Refinement

Atoms O2 and O4 of the dichromate anion are disordered over two positions with occupancies of (0.65/0.35) and (0.70/0.30), respectively. Atom O3 is disordered over three positions, two of which are generated by a crystallographic twofold rotation axis, with occupancies of 0.42 for the major component and of 0.29 for the minor components, respectively. All H atoms were placed in calculated positions and refined using a riding model with C—H = 0.97 Å, N—H = 0.89 Å, and with U_iso(H) = 1.2 U_eq(C) or 1.5 U_eq(N).

Computing details

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids. Symmetry codes: (a) 1.5 - x, 0.5 - y, -z; (b) 1 - x, y, 0.5 - z.
	Fig. 2. Packing diagram of (I) viewed approximately along the b axis. Dashed lines indicate hydrogen bonds.

Bis(ethylenediammonium) dichromate oxalate

Crystal data

(C2H10N2)2[Cr2O7](C2O4)	F(000) = 880
Mr = 428.26	Dx = 1.774 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 25 reflections
a = 19.591 (1) Å	θ = 10.0–10.9°
b = 6.478 (1) Å	µ = 1.42 mm^−1
c = 12.843 (2) Å	T = 293 K
β = 100.36 (2)°	Prism, orange-red
V = 1603.3 (4) Å^3	0.33 × 0.27 × 0.15 mm
Z = 4

Data collection

Enraf–Nonius CAD-4 diffractometer	1615 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.054
Graphite monochromator	θmax = 27.0°, θmin = 2.1°
ω/2θ scans	h = −24→24
Absorption correction: ψ scan (North et al., 1968)	k = −8→2
Tmin = 0.638, Tmax = 0.809	l = 0→16
2306 measured reflections	2 standard reflections every 120 min
1757 independent reflections	intensity decay: 1.0%

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)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.124	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0716P)^2 + 2.7856P] where P = (Fo^2 + 2Fc^2)/3
1757 reflections	(Δ/σ)max < 0.001
136 parameters	Δρmax = 0.50 e Å^−3
15 restraints	Δρmin = −0.69 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 > 2σ(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	Occ. (<1)
Cr	0.56119 (2)	0.41517 (7)	0.35029 (3)	0.0375 (2)
O1	0.53960 (14)	0.2065 (4)	0.4052 (2)	0.0672 (7)
O2	0.6161 (2)	0.3377 (7)	0.2763 (3)	0.0661 (10)	0.65
O2'	0.6416 (3)	0.4485 (13)	0.3638 (7)	0.069 (2)	0.35
O3	0.5000	0.5311 (11)	0.2500	0.054 (2)	0.42
O3'	0.5280 (4)	0.4497 (15)	0.2147 (5)	0.0471 (18)	0.29
O4	0.5936 (3)	0.5807 (6)	0.4300 (4)	0.0844 (15)	0.70
O4'	0.5329 (7)	0.6223 (15)	0.4136 (8)	0.078 (3)	0.30
C1	0.75386 (11)	0.3226 (3)	0.04964 (14)	0.0224 (4)
O5	0.72688 (9)	0.2589 (3)	0.12602 (11)	0.0309 (4)
O6	0.78485 (10)	0.4892 (2)	0.04552 (12)	0.0337 (4)
N1	0.40427 (12)	0.0641 (3)	0.41953 (19)	0.0397 (5)
H1	0.3656	0.1386	0.4144	0.060*
H2	0.4394	0.1460	0.4113	0.060*
H3	0.4135	0.0046	0.4830	0.060*
C2	0.39464 (16)	−0.0993 (4)	0.3351 (3)	0.0478 (7)
H4	0.3761	−0.0365	0.2674	0.057*
H5	0.4394	−0.1591	0.3303	0.057*
N2	0.27317 (10)	−0.2017 (3)	0.34349 (13)	0.0276 (4)
H6	0.2488	−0.2975	0.3704	0.041*
H7	0.2563	−0.1863	0.2748	0.041*
H8	0.2702	−0.0824	0.3767	0.041*
C3	0.34663 (15)	−0.2666 (4)	0.3576 (2)	0.0416 (6)
H9	0.3503	−0.3825	0.3111	0.050*
H10	0.3614	−0.3136	0.4299	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr	0.0342 (3)	0.0480 (3)	0.0272 (3)	−0.00468 (16)	−0.00284 (18)	0.00259 (15)
O1	0.0624 (15)	0.0668 (16)	0.0741 (16)	−0.0276 (13)	0.0170 (12)	0.0129 (13)
O2	0.070 (3)	0.066 (2)	0.071 (2)	0.003 (2)	0.036 (2)	0.008 (2)
O2'	0.032 (3)	0.085 (5)	0.087 (5)	−0.012 (3)	0.002 (3)	0.044 (4)
O3	0.058 (6)	0.027 (3)	0.064 (6)	0.000	−0.028 (5)	0.000
O3'	0.046 (4)	0.065 (5)	0.028 (3)	−0.024 (4)	0.002 (3)	0.006 (3)
O4	0.112 (4)	0.064 (2)	0.064 (2)	−0.024 (2)	−0.018 (3)	−0.0187 (18)
O4'	0.099 (8)	0.057 (5)	0.076 (6)	0.013 (5)	0.008 (6)	−0.034 (4)
C1	0.0278 (10)	0.0223 (9)	0.0167 (8)	0.0025 (7)	0.0028 (7)	0.0011 (7)
O5	0.0443 (9)	0.0333 (8)	0.0168 (7)	−0.0065 (7)	0.0098 (6)	−0.0004 (6)
O6	0.0505 (11)	0.0240 (8)	0.0293 (8)	−0.0079 (7)	0.0147 (7)	−0.0049 (6)
N1	0.0338 (11)	0.0351 (11)	0.0516 (13)	−0.0053 (8)	0.0113 (10)	−0.0069 (9)
C2	0.0413 (15)	0.0466 (15)	0.0603 (18)	−0.0022 (12)	0.0218 (13)	−0.0169 (13)
N2	0.0403 (10)	0.0233 (8)	0.0196 (8)	−0.0022 (7)	0.0064 (7)	−0.0029 (6)
C3	0.0444 (14)	0.0263 (11)	0.0510 (15)	0.0049 (10)	0.0008 (12)	−0.0060 (10)

Geometric parameters (Å, º)

Cr—O4	1.538 (4)	C1—O6	1.244 (3)
Cr—O2'	1.568 (6)	C1—O5	1.264 (2)
Cr—O1	1.615 (2)	C1—C1^ii	1.569 (4)
Cr—O2	1.636 (4)	N1—C2	1.503 (3)
Cr—O4'	1.712 (8)	N1—H1	0.8900
Cr—O3'	1.760 (7)	N1—H2	0.8900
Cr—O3	1.762 (3)	N1—H3	0.8900
Cr—O3'^i	1.810 (8)	C2—C3	1.497 (4)
O2—O2'	1.351 (10)	C2—H4	0.9700
O2'—O4	1.621 (11)	C2—H5	0.9700
O3—O3'^i	0.935 (9)	N2—C3	1.479 (3)
O3—O3'	0.935 (9)	N2—H6	0.8900
O3—Cr^i	1.762 (3)	N2—H7	0.8900
O3'—O3'^i	1.545 (15)	N2—H8	0.8900
O3'—Cr^i	1.810 (8)	C3—H9	0.9700
O4—O4'	1.201 (12)	C3—H10	0.9700
O4—Cr—O2'	62.9 (4)	Cr^i—O3—Cr	129.5 (4)
O4—Cr—O1	113.7 (2)	O3—O3'—Cr	74.7 (4)
O2'—Cr—O1	113.8 (3)	O3'^i—O3'—Cr	66.0 (4)
O4—Cr—O2	111.4 (3)	O3—O3'—Cr^i	72.0 (5)
O2'—Cr—O2	49.8 (4)	O3'^i—O3'—Cr^i	62.7 (5)
O1—Cr—O2	104.35 (18)	Cr—O3'—Cr^i	126.5 (4)
O4—Cr—O4'	42.9 (4)	O4'—O4—Cr	76.3 (4)
O2'—Cr—O4'	104.1 (6)	O4'—O4—O2'	132.6 (6)
O1—Cr—O4'	108.4 (4)	Cr—O4—O2'	59.5 (3)
O2—Cr—O4'	145.0 (5)	O4—O4'—Cr	60.8 (4)
O4—Cr—O3'	127.2 (3)	O6—C1—O5	126.25 (18)
O2'—Cr—O3'	106.1 (4)	O6—C1—C1^ii	117.5 (2)
O1—Cr—O3'	117.3 (3)	O5—C1—C1^ii	116.2 (2)
O2—Cr—O3'	68.2 (3)	C2—N1—H1	109.5
O4'—Cr—O3'	106.1 (5)	C2—N1—H2	109.5
O4—Cr—O3	109.5 (3)	H1—N1—H2	109.5
O2'—Cr—O3	124.1 (3)	C2—N1—H3	109.5
O1—Cr—O3	118.6 (2)	H1—N1—H3	109.5
O2—Cr—O3	97.93 (17)	H2—N1—H3	109.5
O4'—Cr—O3	77.1 (4)	C3—C2—N1	111.9 (2)
O3'—Cr—O3	30.8 (3)	C3—C2—H4	109.2
O4—Cr—O3'^i	118.0 (3)	N1—C2—H4	109.2
O2'—Cr—O3'^i	154.3 (4)	C3—C2—H5	109.2
O1—Cr—O3'^i	89.9 (3)	N1—C2—H5	109.2
O2—Cr—O3'^i	116.8 (3)	H4—C2—H5	107.9
O4'—Cr—O3'^i	75.7 (5)	C3—N2—H6	109.5
O3'—Cr—O3'^i	51.2 (4)	C3—N2—H7	109.5
O3—Cr—O3'^i	30.3 (3)	H6—N2—H7	109.5
O2'—O2—Cr	62.5 (3)	C3—N2—H8	109.5
O2—O2'—Cr	67.7 (4)	H6—N2—H8	109.5
O2—O2'—O4	123.6 (5)	H7—N2—H8	109.5
Cr—O2'—O4	57.6 (3)	N2—C3—C2	113.7 (2)
O3'^i—O3—O3'	111.3 (12)	N2—C3—H9	108.8
O3'^i—O3—Cr^i	74.5 (5)	C2—C3—H9	108.8
O3'—O3—Cr^i	77.7 (5)	N2—C3—H10	108.8
O3'^i—O3—Cr	77.7 (5)	C2—C3—H10	108.8
O3'—O3—Cr	74.5 (5)	H9—C3—H10	107.7

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O5^i	0.89	1.96	2.828 (3)	166
N1—H2···O1	0.89	2.02	2.844 (3)	154
N1—H3···O1^iii	0.89	2.07	2.909 (4)	156
N2—H6···O6^iv	0.89	1.94	2.813 (2)	167
N2—H7···O5^v	0.89	1.93	2.789 (2)	162
N2—H8···O6^vi	0.89	2.22	2.910 (2)	134
N2—H8···O5^i	0.89	2.21	3.010 (2)	149

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