metal-organic compounds
2-Amino-6-methylpyridinium trans-diaquadioxalatochromate(III) monohydrate
aLaboratoire de Matériaux et Cristallochimie, Département de Chimie, Faculté des Sciences, 2092 El Manar, Tunis, Tunisia
*Correspondence e-mail: faouzi.zid@fst.rnu.tn
In the title compound, (C6H9N2)[Cr(C2O4)2(H2O)2]·H2O, the CrIII atom adopts a slightly distorted octahedral coordination environment defined by two chelating oxalate ligands in the equatorial plane and two water molecules in axial positions. A three-dimensional network is generated by intermolecular N—H⋯O and O—H⋯O hydrogen-bonding interactions involving the cation, the complex anion and the lattice water molecule.
Related literature
For general background to the coordination chemistry of oxalates, see: Martin et al. (2007). For the structural characterization of organic–inorganic salts containing the [Cr(C2O4)2(H2O)2]− anion, see: Bélombé et al. (2009); Nenwa et al. (2010); Chérif et al. (2011); Chérif, Abdelhak et al. (2012); Chérif, Zid et al. (2012). For C—O bond lengths in oxalate anions, see: Marinescu et al. (2000). For geometric parameters of the 2-amino-6-methylpyridinium cation, see: Fun et al. (2008, 2009, 2010); Jebas et al. (2009); Quah et al. (2008); Ramesh et al. (2010); Rotondo et al. (2009); Pan et al. (2008). For discussion of hydrogen bonding, see: Blessing (1986); Brown (1976).
Experimental
Crystal data
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Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012).
Supporting information
10.1107/S1600536813022058/mw2113sup1.cif
contains datablocks I, New_Global_Publ_Block. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536813022058/mw2113Isup2.hkl
The title compound was prepared as good quality pink single crystals from a mixture of chromium (III) nitrate nonahydrate, 2-amino-6-methylpyridinium and oxalic acid in a 1:1:1 molar ratio in ethanol and water (50/50 v:v). The resulting mixture was heated to boiling and was stirred for one hour. After two weeks single pink crystals were obtained by slow evaporation at room temperature.
The hydrogen atoms were located in difference Fourier maps. Those attached to carbon were placed in calculated positions (C—H = 0.93 - 0.96 Å) while those attached to nitrogen and oxygen were placed in the experimental positions and their coordinates adjusted to give N—H = 0.93 Å and O—H = 0.83 Å. All were included as riding contributions with isotropic displacement parameters 1.2 - 1.5 times those of the attached atoms.
Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell
CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012).Fig. 1. The asymmetric unit of (C6H9N2)[Cr(H2O)2(C2O4)2].H2O. | |
Fig. 2. Projection of the (C6H9N2)[Cr(H2O)2(C2O4)2].H2O structure along the b axis. | |
Fig. 3. Closeup view of the hydrogen bonding (dotted lines). H atoms not involved in hydrogen bonding have been omitted for clarity. |
(C6H9N2)[Cr(C2O4)2(H2O)2]·H2O | F(000) = 1608 |
Mr = 391.24 | Dx = 1.705 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 25 reflections |
a = 18.572 (3) Å | θ = 10–15° |
b = 11.025 (2) Å | µ = 0.81 mm−1 |
c = 14.975 (3) Å | T = 298 K |
β = 96.28 (2)° | Prism, pink |
V = 3047.8 (10) Å3 | 0.56 × 0.42 × 0.33 mm |
Z = 8 |
Enraf–Nonius CAD-4 diffractometer | 2896 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.037 |
Graphite monochromator | θmax = 27.0°, θmin = 2.2° |
non–profiled ω/2θ scans | h = −23→23 |
Absorption correction: ψ scan (North et al., 1968) | k = −1→14 |
Tmin = 0.679, Tmax = 0.764 | l = −19→3 |
4604 measured reflections | 2 standard reflections every 120 min |
3312 independent reflections | intensity decay: 3.2% |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.040 | Hydrogen site location: mixed |
wR(F2) = 0.112 | H-atom parameters constrained |
S = 1.07 | w = 1/[σ2(Fo2) + (0.0677P)2 + 2.2239P] where P = (Fo2 + 2Fc2)/3 |
3312 reflections | (Δ/σ)max = 0.001 |
218 parameters | Δρmax = 0.65 e Å−3 |
0 restraints | Δρmin = −0.45 e Å−3 |
(C6H9N2)[Cr(C2O4)2(H2O)2]·H2O | V = 3047.8 (10) Å3 |
Mr = 391.24 | Z = 8 |
Monoclinic, C2/c | Mo Kα radiation |
a = 18.572 (3) Å | µ = 0.81 mm−1 |
b = 11.025 (2) Å | T = 298 K |
c = 14.975 (3) Å | 0.56 × 0.42 × 0.33 mm |
β = 96.28 (2)° |
Enraf–Nonius CAD-4 diffractometer | 2896 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.037 |
Tmin = 0.679, Tmax = 0.764 | 2 standard reflections every 120 min |
4604 measured reflections | intensity decay: 3.2% |
3312 independent reflections |
R[F2 > 2σ(F2)] = 0.040 | 0 restraints |
wR(F2) = 0.112 | H-atom parameters constrained |
S = 1.07 | Δρmax = 0.65 e Å−3 |
3312 reflections | Δρmin = −0.45 e Å−3 |
218 parameters |
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. |
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. |
x | y | z | Uiso*/Ueq | ||
Cr1 | 0.32255 (2) | 0.27746 (3) | 0.19839 (2) | 0.02219 (13) | |
O1 | 0.38682 (8) | 0.29143 (13) | 0.09943 (9) | 0.0291 (3) | |
H3 | 0.3720 | 0.2466 | 0.0568 | 0.044* | |
H4 | 0.4279 | 0.2639 | 0.1150 | 0.044* | |
O2 | 0.25655 (9) | 0.26707 (13) | 0.29364 (10) | 0.0325 (3) | |
H2 | 0.2587 | 0.3260 | 0.3284 | 0.049* | |
H10 | 0.2578 | 0.2050 | 0.3251 | 0.049* | |
O3 | 0.24053 (8) | 0.26015 (12) | 0.10486 (9) | 0.0259 (3) | |
O4 | 0.40928 (8) | 0.28451 (13) | 0.28656 (10) | 0.0315 (3) | |
O5 | 0.29813 (8) | 0.45160 (12) | 0.18501 (10) | 0.0290 (3) | |
O6 | 0.33921 (8) | 0.10332 (13) | 0.20991 (9) | 0.0284 (3) | |
O7 | 0.15703 (8) | 0.37130 (15) | 0.02425 (10) | 0.0379 (4) | |
O8 | 0.22682 (10) | 0.57497 (14) | 0.09691 (10) | 0.0374 (4) | |
O9 | 0.40914 (10) | −0.03256 (15) | 0.28778 (13) | 0.0468 (4) | |
O10 | 0.49100 (8) | 0.16363 (17) | 0.36144 (11) | 0.0389 (4) | |
O11 | 0.24742 (10) | −0.05094 (17) | 0.09548 (11) | 0.0480 (5) | |
H1 | 0.2610 | −0.0620 | 0.0451 | 0.072* | |
H11 | 0.2725 | 0.0015 | 0.1239 | 0.072* | |
N1 | 0.49218 (10) | 0.78135 (16) | 0.37925 (13) | 0.0325 (4) | |
H7 | 0.4632 | 0.8434 | 0.3532 | 0.039* | |
N2 | 0.56211 (12) | 0.93977 (19) | 0.43928 (15) | 0.0455 (5) | |
H5 | 0.6002 | 0.9646 | 0.4807 | 0.055* | |
H13 | 0.5320 | 0.9978 | 0.4096 | 0.055* | |
C1 | 0.21055 (11) | 0.35961 (17) | 0.07919 (12) | 0.0246 (4) | |
C2 | 0.43552 (11) | 0.1812 (2) | 0.31024 (13) | 0.0281 (4) | |
C3 | 0.24748 (11) | 0.47407 (17) | 0.12350 (13) | 0.0254 (4) | |
C4 | 0.39248 (11) | 0.07128 (19) | 0.26753 (14) | 0.0288 (4) | |
C5 | 0.52196 (14) | 0.5768 (2) | 0.4038 (2) | 0.0480 (6) | |
H12 | 0.5124 | 0.4947 | 0.3949 | 0.058* | |
C6 | 0.58452 (15) | 0.6150 (3) | 0.4566 (2) | 0.0518 (7) | |
H9 | 0.6165 | 0.5570 | 0.4830 | 0.062* | |
C7 | 0.59978 (14) | 0.7335 (3) | 0.47029 (18) | 0.0449 (6) | |
H6 | 0.6416 | 0.7570 | 0.5061 | 0.054* | |
C8 | 0.47476 (13) | 0.6629 (2) | 0.36524 (17) | 0.0397 (5) | |
C9 | 0.40503 (15) | 0.6364 (3) | 0.3091 (2) | 0.0587 (8) | |
H8 | 0.3659 | 0.6395 | 0.3460 | 0.088* | |
H14 | 0.4072 | 0.5570 | 0.2832 | 0.088* | |
H15 | 0.3971 | 0.6956 | 0.2621 | 0.088* | |
C10 | 0.55186 (12) | 0.8210 (2) | 0.42989 (15) | 0.0337 (5) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cr1 | 0.02305 (19) | 0.01884 (19) | 0.02292 (19) | 0.00059 (11) | −0.00543 (12) | 0.00012 (10) |
O1 | 0.0281 (7) | 0.0301 (7) | 0.0279 (7) | −0.0021 (6) | −0.0021 (6) | −0.0019 (6) |
O2 | 0.0400 (8) | 0.0271 (8) | 0.0304 (8) | 0.0037 (6) | 0.0047 (6) | 0.0027 (6) |
O3 | 0.0260 (7) | 0.0220 (7) | 0.0278 (7) | −0.0003 (5) | −0.0059 (5) | −0.0012 (5) |
O4 | 0.0305 (8) | 0.0311 (8) | 0.0302 (8) | −0.0023 (6) | −0.0088 (6) | −0.0015 (6) |
O5 | 0.0329 (7) | 0.0200 (6) | 0.0317 (7) | 0.0001 (6) | −0.0071 (6) | −0.0014 (5) |
O6 | 0.0272 (7) | 0.0228 (7) | 0.0330 (7) | 0.0015 (6) | −0.0062 (6) | 0.0006 (6) |
O7 | 0.0356 (8) | 0.0361 (8) | 0.0377 (8) | 0.0107 (7) | −0.0152 (7) | −0.0085 (7) |
O8 | 0.0545 (10) | 0.0220 (7) | 0.0333 (8) | 0.0083 (7) | −0.0054 (7) | 0.0007 (6) |
O9 | 0.0468 (10) | 0.0309 (9) | 0.0602 (11) | 0.0099 (7) | −0.0058 (8) | 0.0134 (8) |
O10 | 0.0261 (7) | 0.0521 (10) | 0.0359 (8) | 0.0011 (7) | −0.0087 (6) | 0.0098 (7) |
O11 | 0.0649 (12) | 0.0413 (10) | 0.0375 (9) | −0.0201 (9) | 0.0042 (8) | 0.0002 (7) |
N1 | 0.0279 (9) | 0.0289 (9) | 0.0396 (10) | 0.0063 (7) | −0.0012 (7) | 0.0018 (7) |
N2 | 0.0462 (12) | 0.0356 (10) | 0.0534 (12) | −0.0063 (9) | −0.0005 (9) | −0.0046 (9) |
C1 | 0.0270 (9) | 0.0249 (10) | 0.0214 (9) | 0.0032 (7) | −0.0002 (7) | −0.0016 (7) |
C2 | 0.0229 (9) | 0.0371 (11) | 0.0240 (9) | 0.0005 (8) | 0.0003 (7) | 0.0042 (8) |
C3 | 0.0316 (10) | 0.0229 (9) | 0.0215 (9) | 0.0017 (7) | 0.0015 (7) | −0.0015 (7) |
C4 | 0.0264 (10) | 0.0280 (10) | 0.0312 (10) | 0.0029 (8) | 0.0005 (8) | 0.0053 (8) |
C5 | 0.0487 (15) | 0.0287 (11) | 0.0673 (17) | 0.0031 (11) | 0.0094 (13) | 0.0012 (11) |
C6 | 0.0435 (14) | 0.0473 (14) | 0.0639 (17) | 0.0152 (12) | 0.0029 (12) | 0.0120 (13) |
C7 | 0.0331 (12) | 0.0506 (15) | 0.0486 (14) | 0.0068 (10) | −0.0061 (11) | 0.0036 (11) |
C8 | 0.0338 (11) | 0.0353 (12) | 0.0509 (14) | −0.0016 (9) | 0.0087 (10) | −0.0066 (10) |
C9 | 0.0378 (13) | 0.0634 (19) | 0.0733 (19) | −0.0083 (13) | −0.0011 (13) | −0.0253 (15) |
C10 | 0.0295 (10) | 0.0381 (12) | 0.0334 (11) | 0.0027 (9) | 0.0028 (8) | 0.0033 (9) |
Cr1—O6 | 1.9493 (15) | N1—C10 | 1.346 (3) |
Cr1—O3 | 1.9626 (14) | N1—C8 | 1.357 (3) |
Cr1—O4 | 1.9695 (15) | N1—H7 | 0.9300 |
Cr1—O5 | 1.9778 (15) | N2—C10 | 1.328 (3) |
Cr1—O2 | 1.9830 (15) | N2—H5 | 0.9300 |
Cr1—O1 | 2.0080 (15) | N2—H13 | 0.9300 |
O1—H3 | 0.8300 | C1—C3 | 1.550 (3) |
O1—H4 | 0.8300 | C2—C4 | 1.551 (3) |
O2—H2 | 0.8299 | C5—C8 | 1.375 (4) |
O2—H10 | 0.8300 | C5—C6 | 1.397 (4) |
O3—C1 | 1.270 (2) | C5—H12 | 0.9300 |
O4—C2 | 1.274 (3) | C6—C7 | 1.348 (4) |
O5—C3 | 1.267 (2) | C6—H9 | 0.9300 |
O6—C4 | 1.289 (2) | C7—C10 | 1.404 (3) |
O7—C1 | 1.226 (2) | C7—H6 | 0.9300 |
O8—C3 | 1.229 (2) | C8—C9 | 1.494 (4) |
O9—C4 | 1.216 (3) | C9—H8 | 0.9600 |
O10—C2 | 1.231 (2) | C9—H14 | 0.9600 |
O11—H1 | 0.8299 | C9—H15 | 0.9600 |
O11—H11 | 0.8301 | ||
O6—Cr1—O3 | 94.05 (6) | O7—C1—C3 | 119.34 (17) |
O6—Cr1—O4 | 82.49 (6) | O3—C1—C3 | 114.48 (16) |
O3—Cr1—O4 | 175.08 (6) | O10—C2—O4 | 125.7 (2) |
O6—Cr1—O5 | 175.89 (6) | O10—C2—C4 | 119.50 (19) |
O3—Cr1—O5 | 82.57 (6) | O4—C2—C4 | 114.82 (16) |
O4—Cr1—O5 | 101.03 (6) | O8—C3—O5 | 126.40 (19) |
O6—Cr1—O2 | 89.09 (6) | O8—C3—C1 | 119.36 (18) |
O3—Cr1—O2 | 90.87 (7) | O5—C3—C1 | 114.24 (16) |
O4—Cr1—O2 | 92.56 (7) | O9—C4—O6 | 125.5 (2) |
O5—Cr1—O2 | 88.63 (6) | O9—C4—C2 | 121.83 (19) |
O6—Cr1—O1 | 92.26 (6) | O6—C4—C2 | 112.65 (17) |
O3—Cr1—O1 | 87.62 (6) | C8—C5—C6 | 118.9 (2) |
O4—Cr1—O1 | 89.03 (6) | C8—C5—H12 | 120.6 |
O5—Cr1—O1 | 89.94 (6) | C6—C5—H12 | 120.6 |
O2—Cr1—O1 | 178.04 (6) | C7—C6—C5 | 121.7 (2) |
Cr1—O1—H3 | 110.3 | C7—C6—H9 | 119.1 |
Cr1—O1—H4 | 111.5 | C5—C6—H9 | 119.1 |
H3—O1—H4 | 102.5 | C6—C7—C10 | 119.2 (2) |
Cr1—O2—H2 | 114.5 | C6—C7—H6 | 120.4 |
Cr1—O2—H10 | 118.3 | C10—C7—H6 | 120.4 |
H2—O2—H10 | 107.0 | N1—C8—C5 | 118.0 (2) |
C1—O3—Cr1 | 114.35 (12) | N1—C8—C9 | 116.9 (2) |
C2—O4—Cr1 | 114.29 (13) | C5—C8—C9 | 125.1 (2) |
C3—O5—Cr1 | 114.03 (12) | C8—C9—H8 | 109.5 |
C4—O6—Cr1 | 115.59 (13) | C8—C9—H14 | 109.5 |
H1—O11—H11 | 111.1 | H8—C9—H14 | 109.5 |
C10—N1—C8 | 124.6 (2) | C8—C9—H15 | 109.5 |
C10—N1—H7 | 113.7 | H8—C9—H15 | 109.5 |
C8—N1—H7 | 121.7 | H14—C9—H15 | 109.5 |
C10—N2—H5 | 116.8 | N2—C10—N1 | 118.7 (2) |
C10—N2—H13 | 123.8 | N2—C10—C7 | 123.7 (2) |
H5—N2—H13 | 119.3 | N1—C10—C7 | 117.6 (2) |
O7—C1—O3 | 126.18 (18) | ||
Cr1—O3—C1—O7 | −177.14 (17) | O4—C2—C4—O9 | −176.0 (2) |
Cr1—O3—C1—C3 | 3.0 (2) | O10—C2—C4—O6 | −174.65 (18) |
Cr1—O4—C2—O10 | 176.81 (17) | O4—C2—C4—O6 | 4.3 (3) |
Cr1—O4—C2—C4 | −2.0 (2) | C8—C5—C6—C7 | −0.3 (4) |
Cr1—O5—C3—O8 | −173.21 (18) | C5—C6—C7—C10 | −0.5 (4) |
Cr1—O5—C3—C1 | 6.1 (2) | C10—N1—C8—C5 | −1.4 (4) |
O7—C1—C3—O8 | −6.7 (3) | C10—N1—C8—C9 | 178.2 (2) |
O3—C1—C3—O8 | 173.12 (19) | C6—C5—C8—N1 | 1.2 (4) |
O7—C1—C3—O5 | 173.94 (18) | C6—C5—C8—C9 | −178.4 (3) |
O3—C1—C3—O5 | −6.2 (2) | C8—N1—C10—N2 | −179.0 (2) |
Cr1—O6—C4—O9 | 175.95 (19) | C8—N1—C10—C7 | 0.7 (4) |
Cr1—O6—C4—C2 | −4.4 (2) | C6—C7—C10—N2 | −180.0 (2) |
O10—C2—C4—O9 | 5.1 (3) | C6—C7—C10—N1 | 0.3 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H3···O7i | 0.83 | 1.82 | 2.643 (2) | 171 |
O1—H4···O10ii | 0.83 | 1.87 | 2.681 (2) | 165 |
O2—H2···O11iii | 0.83 | 1.78 | 2.611 (2) | 173 |
O2—H10···O8iv | 0.83 | 1.85 | 2.675 (2) | 172 |
N1—H7···O9v | 0.93 | 1.90 | 2.829 (2) | 174 |
N2—H5···O7vi | 0.93 | 2.16 | 2.928 (3) | 139 |
N2—H13···O10v | 0.93 | 2.08 | 2.976 (3) | 162 |
C9—H8···O3iii | 0.96 | 2.56 | 3.405 (3) | 147 |
C9—H14···O5 | 0.96 | 2.64 | 3.277 (3) | 124 |
O11—H1···O8i | 0.83 | 2.17 | 2.983 (2) | 167 |
O11—H11···O6 | 0.83 | 2.03 | 2.845 (2) | 169 |
Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) −x+1, y, −z+1/2; (iii) −x+1/2, y+1/2, −z+1/2; (iv) −x+1/2, y−1/2, −z+1/2; (v) x, y+1, z; (vi) x+1/2, −y+3/2, z+1/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H3···O7i | 0.83 | 1.82 | 2.643 (2) | 171 |
O1—H4···O10ii | 0.83 | 1.87 | 2.681 (2) | 165 |
O2—H2···O11iii | 0.83 | 1.78 | 2.611 (2) | 173 |
O2—H10···O8iv | 0.83 | 1.85 | 2.675 (2) | 172 |
N1—H7···O9v | 0.93 | 1.90 | 2.829 (2) | 174 |
N2—H5···O7vi | 0.93 | 2.16 | 2.928 (3) | 139 |
N2—H13···O10v | 0.93 | 2.08 | 2.976 (3) | 162 |
C9—H8···O3iii | 0.96 | 2.56 | 3.405 (3) | 147 |
C9—H14···O5 | 0.96 | 2.64 | 3.277 (3) | 124 |
O11—H1···O8i | 0.83 | 2.17 | 2.983 (2) | 167 |
O11—H11···O6 | 0.83 | 2.03 | 2.845 (2) | 169 |
Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) −x+1, y, −z+1/2; (iii) −x+1/2, y+1/2, −z+1/2; (iv) −x+1/2, y−1/2, −z+1/2; (v) x, y+1, z; (vi) x+1/2, −y+3/2, z+1/2. |
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The coordination chemistry of oxalates (C2O42-) continues to receive considerable attention, largely due to the ability of this ion to act as a remarkably flexible ligand system in complexations with a wide range of metal ions (Martin et al., 2007). Recently, certain hybrid organic-inorganic salts were reported of formula A[Cr(H2O)2(C2O4)2].xH2O (A+ = aromatic iminium cation, 0 ≤ x ≤ 1) (Bélombé et al., 2009; Nenwa et al., 2010; Chérif et al., 2011; Chérif, Abdelhak et al., 2012; Chérif, Zid et al., 2012). These salts form different crystalline structures depending on the nature of the substituent and/or substitution position on the ring of the pyridinium cation (Chérif, Abdelhak et al., 2011, 2012; Chérif, Zid et al., 2012; Nenwa et al., 2010). In a continuation of these studies, we report the structure of (amp)[Cr(C2O4)2(H2O)2].H2O (amp = 2-amino-6-methylpyridinium ion) with the anion having trans-geometry. The asymmetric unit of the title compound consists a [Cr(C2O4)2(H2O)2]- anion, a (C6H9N2)+ cation and one uncoordinated water molecule (Figure 1). The coordination environment of the chromium(III) is distorted octahedral since the O—Cr—O angles vary from 82.48 (6)° to 101.02 (6)° while the four Cr—O (ox) distances are slightly shorter than the two Cr—O(water) distances. Similar patterns of distortion have been observed in homologous salts involving quinolinium (C9H8N)+, 4-dimethylaminopyridinium (C7H11N2)+ and 4-aminopyridinium (C5H7N2)+ cations (Bélombé et al., 2009; Nenwa et al., 2010; Chérif et al., 2011). The bond distances for the oxalate ions compare well with those reported for other oxalate complexes (Marinescu et al., 2000) as do the main geometric parameters of the (C6H9N2)+ cation (Fun et al., 2008, 2009, 2010; Jebas et al., 2009; Quah et al., 2008; Ramesh et al., 2010; Rotondo et al., 2009; Pan et al., 2008; Chérif et al., 2011). The cations are located between the anions (Fig. 2) and within the cation layer, the methyl groups of each pair of closest cations point in opposite directions. The crystal packing is stabilized by N—H···O and O—H···O hydrogen bonds (Blessing, 1986; Brown, 1976) between (C6H9N2)+ and [Cr(C2O4)2(H2O)2]- involving the uncoordinated water molecule (O11) as both acceptor and donor and the coordinated water molecules (O1 and O2) only as donors. These interactions link the layers together forming a three-dimensional network and reinforcing the cohesion of the ionic structure.