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A new organic chromate, [(CH3)3CNH3]2[CrO4], associated with the monoprotonated 2-methyl-2-propan­amine mol­ecule, has been synthesized. The structure of the compound consists of discrete chromate ions stacked in layers perpendicular to the (010) plane, separated by organic layers containing [(CH3)3CNH3]+ groups. The cohesion and stability of the structure are ensured by a two-dimensional network of hydrogen bonds in the (001) plane, where the O atoms of the anion are acceptors from the 2-methyl-2-propan­ammonium N-H groups.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks I, global


Structure factor file (CIF format)
Contains datablock I

CCDC reference: 197454

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.003 Å
  • Disorder in solvent or counterion
  • R factor = 0.036
  • wR factor = 0.090
  • Data-to-parameter ratio = 15.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

Yellow Alert Alert Level C:
PLAT_302 Alert C Anion/Solvent Disorder ....................... 17.00 Perc.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check

Comment top

The present description of the bis(2-methyl-2-propanammonium)chromate structure is part of an investigation of materials resulting from interaction between chromic acid and organic molecules, as amines and aminoalcohols. Among the investigated materials, we have previously described 2,2-dimethyl-1,3-propanediammonium chromate (Chebbi et al., 2000), 4-ammonio-2,2,6,6-tetramethylpiperidinium chromate dihydrate (Chebbi & Driss, 2001) and 1,4-butanediammonium chromate (Chebbi & Driss, 2002). Furthermore, the literature gives some examples of CrO42− associated to organic cation: 2(CN3H6)+·CrO42− (Cygler et al. 1976) and 2[(CH3)4N]+·CrO42−.xH2O (x = 0.5 or 2; Sorehkin et al., 1978). Two components, inorganic CrO42− and organic [(CH3)3CNH3]+, build up the atomic arrangement of [(CH3)3CNH3]2[CrO4], (I) (Fig. 1). Six chromate layers per cell coexist parallel to (001) planes at zi = 2i + 1/12 (0 i 5), while the organic groups provide the cohesion in layers through N—H···O hydrogen bonds (Fig. 2). The network of CrO42− lies between two networks of cations without interconnection between successive layers. The CrO42− anion has local 3 m symmetry instead of regular −43m symmetry and the charge is compensated by the 2-methyl-2-propanammonium cations. The Cr atom is delocalized in two positions, separated by 0.9 Å and having an occupancy of 0.5 each. The Cr—O distances within the distorted tetrahedron CrO4 vary from 1.620 (5) to 1.632 (2) Å. In addition, the O—Cr—O angle values differ significantly from the ideal value 109.5° and vary from 106.77 (4) to 112.03 (3)°. These values are generally observed for this type of tetrahedron (Gerault et al., 1987; Bars et al., 1977; Stephens et al., 1969; Brauer et al., 1990). With regard to the geometry of the anion, there is a slight dissymmetry in the Cr—-O bond lengths; the Cr–O1 bond is significantly shorter than the other three. This probably reflects the fact that atom O1 is not involved in any hydrogen bond. The 2-methyl-2-propanammonium groups establish hydrogen bond involving the H atoms of the NH3 groups: one N—H···O bond has an N···O distance of 2.806 (2) Å and participates in the cohesion of the two-dimensional network. The N—C and C—C distances, and C—C—N and C—C—C angles in this organic group are comparable whith those observed for other compounds (Cygler et al. 1976; Chebbi et al., 2000; Chebbi & Driss, 2001, 2002).

Experimental top

The title compound was prepared from a 1:2:100 mixture of CrO3 (2 g), C4H11N (4.84 g) and H2O (36 g). Yellow single crystals suitable of X-ray analysis were obtained from the solution by slow evaporation of the solvent at room temperature.

Refinement top

H atoms of methyl groups were placed at calculated positions and refined as riding, with C—H = 0.96 Å. Atom H4 bonded to N was located in difference Fourier calculations and was refined isotropically. The Cr atom is disordred over two positions, separated by about 0.9 Å, and these positions were refined with half occupancies. One non-equivalent O atom was located around the Cr atom and its position was refined with a site occupancy of 0.5

Computing details top

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

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) (PLATON; Spek, 1990). Atoms Cr1 and O1 have a site-occupation factor of 0.5.
[Figure 2] Fig. 2. Projection along the c direction of (I), with dashed lines indicating hydrogen bonds.
Bis(2-methyl-2-propanammonium) chromate top
Crystal data top
(C4H12N)2[CrO4]Dx = 1.239 Mg m3
Mr = 264.29Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3cCell parameters from 15 reflections
Hall symbol: -R 3 2"cθ = 11–14°
a = 6.720 (1) ŵ = 0.81 mm1
c = 54.330 (9) ÅT = 293 K
V = 2124.8 (6) Å3Hexagonal prism, yellow
Z = 60.28 × 0.25 × 0.14 mm
F(000) = 852
Data collection top
Enraf-Nonius CAD-4
359 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.057
Graphite monochromatorθmax = 27.0°, θmin = 3.6°
ω/2θ scansh = 08
Absorption correction: ψ scan
(North et al., 1968)
k = 80
Tmin = 0.802, Tmax = 0.893l = 6969
1936 measured reflections2 standard reflections every 120 min
524 independent reflections intensity decay: 0.4%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.091H atoms treated by a mixture of independent and constrained refinement
S = 1.37 w = 1/[σ2(Fo2) + (0.02P)2 + 0.149P]
where P = (Fo2 + 2Fc2)/3
524 reflections(Δ/σ)max < 0.001
35 parametersΔρmax = 0.17 e Å3
0 restraintsΔρmin = 0.16 e Å3
Crystal data top
(C4H12N)2[CrO4]Z = 6
Mr = 264.29Mo Kα radiation
Trigonal, R3cµ = 0.81 mm1
a = 6.720 (1) ÅT = 293 K
c = 54.330 (9) Å0.28 × 0.25 × 0.14 mm
V = 2124.8 (6) Å3
Data collection top
Enraf-Nonius CAD-4
359 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.057
Tmin = 0.802, Tmax = 0.8932 standard reflections every 120 min
1936 measured reflections intensity decay: 0.4%
524 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0360 restraints
wR(F2) = 0.091H atoms treated by a mixture of independent and constrained refinement
S = 1.37Δρmax = 0.17 e Å3
524 reflectionsΔρmin = 0.16 e Å3
35 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*/UeqOcc. (<1)
Cr10.66670.33330.07467 (2)0.0349 (3)0.50
O10.66670.33330.04485 (9)0.0600 (12)0.50
O20.4342 (3)0.1009 (3)0.08330.0648 (7)
N10.33330.66670.06612 (5)0.0441 (6)
C10.33330.66670.03843 (6)0.0548 (8)
C20.2382 (6)0.4187 (4)0.03014 (5)0.0860 (9)
H10.33590.36290.03610.102 (11)*
H20.23250.41170.01250.096 (9)*
H30.08620.32540.03670.109 (11)*
H40.372 (4)0.808 (3)0.0728 (3)0.060 (6)*
Atomic displacement parameters (Å2) top
Cr10.0242 (3)0.0242 (3)0.0561 (6)0.01211 (15)0.0000.000
O10.0616 (18)0.0616 (18)0.057 (2)0.0308 (9)0.0000.000
O20.0394 (7)0.0394 (7)0.0868 (15)0.0019 (9)0.0153 (7)0.0153 (7)
N10.0391 (8)0.0391 (8)0.0542 (15)0.0195 (4)0.0000.000
C10.0554 (11)0.0554 (11)0.0536 (17)0.0277 (6)0.0000.000
C20.100 (3)0.0780 (17)0.0782 (17)0.044 (2)0.0000 (17)0.0242 (14)
Geometric parameters (Å, º) top
Cr1—O11.620 (5)C1—C21.524 (3)
Cr1—O21.632 (2)C2—H10.96
N1—C11.505 (4)C2—H20.96
N1—H40.925 (18)C2—H30.96
O1—Cr1—O2106.77 (4)C1—C2—H2109.5
O2i—Cr1—O2112.03 (3)H1—C2—H2109.5
C1—N1—H4113.2 (12)C1—C2—H3109.5
N1—C1—C2107.17 (17)H1—C2—H3109.5
C2ii—C1—C2111.67 (15)H2—C2—H3109.5
Symmetry codes: (i) y+1, xy, z; (ii) y+1, xy+1, z.
Hydrogen-bond geometry (Å, º) top
N1—H4···O2iii0.92 (2)1.88 (2)2.806 (2)176 (2)
Symmetry code: (iii) x, y+1, z.

Experimental details

Crystal data
Chemical formula(C4H12N)2[CrO4]
Crystal system, space groupTrigonal, R3c
Temperature (K)293
a, c (Å)6.720 (1), 54.330 (9)
V3)2124.8 (6)
Radiation typeMo Kα
µ (mm1)0.81
Crystal size (mm)0.28 × 0.25 × 0.14
Data collection
DiffractometerEnraf-Nonius CAD-4
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.802, 0.893
No. of measured, independent and
observed [I > 2σ(I)] reflections
1936, 524, 359
(sin θ/λ)max1)0.638
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.091, 1.37
No. of reflections524
No. of parameters35
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.17, 0.16

Computer programs: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992), CAD-4 EXPRESS, MolEN (Fair, 1990), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1998), SHELXL97.

Selected geometric parameters (Å, º) top
Cr1—O11.620 (5)N1—C11.505 (4)
Cr1—O21.632 (2)C1—C21.524 (3)
O1—Cr1—O2106.77 (4)N1—C1—C2107.17 (17)
O2i—Cr1—O2112.03 (3)C2ii—C1—C2111.67 (15)
Symmetry codes: (i) y+1, xy, z; (ii) y+1, xy+1, z.
Hydrogen-bond geometry (Å, º) top
N1—H4···O2iii0.92 (2)1.88 (2)2.806 (2)176 (2)
Symmetry code: (iii) x, y+1, z.

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