4-(Dimethyl­amino)­pyridinium trans-diaqua­bis­[oxalato(2−)-κ2 O 1,O 2]chromate(III)

Justin Nenwa; Michel M Belombe; Jean Ngoune; Boniface P T Fokwa

doi:10.1107/S1600536810040353

. 2010 Oct 13;66(Pt 11):m1410. doi: 10.1107/S1600536810040353

4-(Dimethylamino)pyridinium trans-diaquabis[oxalato(2−)-κ² O ¹,O ²]chromate(III)

Justin Nenwa ^a,^*, Michel M Belombe ^a, Jean Ngoune ^b, Boniface P T Fokwa ^c

PMCID: PMC3009100 PMID: 21588840

Abstract

In the title salt, (C₇H₁₁N₂)[Cr(C₂O₄)₂(H₂O)₂], the asymmetric unit contains one half-cation and one half-anion. The Cr atom, the C and N atoms involved in C— N(exocyclic) bonding and the N and H atoms of N—H groups lie on twofold rotation axis. The Cr^III atom of the complex anion is six-coordinated in a distorted (4 + 2) octahedral geometry with four equatorial O atoms of two nearly coplanar oxalate and two quasi-axial aqua O atoms. In the crystal, the protonated N atoms of the pyridine rings are hydrogen bonded to the carbonyl O atoms of the anions, forming chains along [010]. These chains are connected by lateral O—H⋯O hydrogen bonds, stabilizing the structure.

Related literature

For general background to the coordination chemistry of oxalate, see: Martin et al. (2007 ▶). For related structures, see: Bélombé et al. (2009 ▶); Ghouili et al. (2010 ▶).

Experimental

Crystal data

(C₇H₁₁N₂)[Cr(C₂O₄)₂(H₂O)₂]
M _r = 387.25
Monoclinic,
a = 11.524 (4) Å
b = 20.372 (8) Å
c = 7.355 (2) Å
β = 120.626 (6)°
V = 1485.9 (9) Å³
Z = 4
Mo Kα radiation
μ = 0.83 mm⁻¹
T = 293 K
0.20 × 0.20 × 0.10 mm

Data collection

Bruker APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ▶) T _min = 0.895, T _max = 0.910
10203 measured reflections
1857 independent reflections
1739 reflections with I > 2σ(I)
R _int = 0.046

Refinement

R[F ² > 2σ(F ²)] = 0.033
wR(F ²) = 0.089
S = 1.16
1857 reflections
127 parameters
2 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.37 e Å⁻³
Δρ_min = −0.38 e Å⁻³

Data collection: SMART (Bruker, 2004 ▶); cell refinement: SAINT (Bruker, 2004 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2010 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810040353/bx2312sup1.cif

e-66-m1410-sup1.cif^{(16.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810040353/bx2312Isup2.hkl

e-66-m1410-Isup2.hkl^{(89.6KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1A⋯O4ⁱ	0.82 (1)	1.91 (1)	2.719 (2)	171 (2)
O1—H1B⋯O5ⁱⁱ	0.80 (1)	1.91 (1)	2.680 (2)	160 (2)
N12—H12⋯O4ⁱⁱⁱ	0.86	2.19	2.906 (3)	141
N12—H12⋯O4^iv	0.86	2.19	2.906 (3)	141

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

Acknowledgments

The authors thank Pr. Barthelemy Nyasse (Organic Chemistry Department, University of Yaounde I) for the donation of 4-dimethylaminopyridine and Klaus Kruse (RWTH Aachen) for his technical support during the X-ray experiments.

supplementary crystallographic information

Comment

The coordination chemistry of oxalate (C₂O₄^2-) continues receiving considerable attention, 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, we published the structure of an organic-inorganic hybrid salt involving the quinolinium cation, [C₉H₈N]⁺and complex anion, [Cr(H₂O)₂(C₂O₄)₂]^-(Bélombé et al., 2009). We report here the crystal structure of a homologous salt, with 4-Dimethylaminopyridinium as the organic cation. The Fig. 1 shows the 4-dimethylaminopyridinium cation, [C₇H₁₁N₂]⁺, and the complex anion, [Cr(H₂O)₂(C₂O₄)₂]^-.The asymmetric unit is formed by one-half cation and one-half anion. The geometrical parameters of the [C₇H₁₁N₂]⁺ cation are in agreement with those found in salts with the same cationic entity (Ghouili et al., 2010). The Cr^III ion of the complex anion adopts a distorted (4 + 2) octahedral coordination involving four equatorial O atoms (O2, O2ⁱ, O3, O3ⁱ) of two nearly coplanar oxalate and two quasi axial O atoms (O1, O1ⁱ) of water ligands (Fig. 1). The equatorial Cr–O distances are 1.9706 (13) Å (Cr–O(2), Cr–O(2ⁱ)) and 1.9468 (13) Å (Cr–O(3), Cr–O(3ⁱ)) respectively, and are significantly shorter than the axial Cr–O distance of 2.0055 (14)Å (Cr–O(1), Cr–O(1ⁱ)). The bond distances in the complex anion are comparable with those reported for the quinolinium compound (Bélombé et al., 2009).In the crystal structure, intermolecular N–H···O(carbonyl) hydrogen bonds connect the ionic entities, generating layers parallel to [010]. These layers are further connected by lateral O–H···O hydrogen bonds,stabilizing the structure (Table 1, Fig. 2)

Experimental

A mixture of 4-dimethylaminopyridine (1 mmol, 122.2 mg) and oxalic acid (2.2 mmol, 277.2 mg) was dissolved in 30 ml of water. The filtered solution was stirred at 328 K and an aqueous solution (20 ml) of CrCl₃.6H₂O (1 mmol, 266.5 mg) was added in successive small portions and stirred for 2 h continuously. The final red-violet solution obtained was left at room temperature and brown plate-like crystals suitable for X-ray diffraction were obtained after a few days.