Sonochemical synthesis and crystal structure of dimethylammonium bis[3-carboxy-2-(dimethylamino)propanoato-κ2 N,O 1]chloridochromium(II) monohydrate

The title complex was synthesized sonochemically. The ligand was formed in situ by hydroamination of fumaric acid. In the crystal, extensive hydrogen bonding, with the dimethylammonium cation and the water molecule linking the complex anions, results in the formation of a supramolecular framework.

The title complex, [(CH 3 ) 2 NH 2 ][Cr(C 6 H 10 NO 4 ) 2 Cl]ÁH 2 O, was synthesized sonochemically. The complex anion consists of a chromium(II) ion ligated by two 3-carboxy-2-(dimethylamino)propanoate anions. They coordinate in a bidentate manner, with a carboxylate oxygen atom and the nitrogen atom cis to each other in the equatorial plane, while the apical position is occupied by a Cl À ion. Hence, the chromium(II) ion is five-coordinate with a quasi-ideal squarepyramidal geometry; 5 parameter = 0.01. The complex crystallizes as a monohydrate and in the crystal, the water molecule and the dimethylammonium counter-ion link the complex cations via N-HÁ Á ÁO, N-HÁ Á ÁCl, O water -HÁ Á ÁO, O-HÁ Á ÁO water and O-HÁ Á ÁO hydrogen bonds, forming a supramolecular framework. There are also a number of C-HÁ Á ÁO hydrogen bonds present that reinforce the framework structure. The crystal studied was refined as a racemic twin.

Chemical context
Fumaric acid, also known as trans-butenedioic acid, boletic acid, lichenic acid or allomaleic acid, occurs naturally in many plants and is named after Fumaria officinalis, a climbing annual plant (Felthouse et al., 2001). Besides being 'practically non-toxic' (European Commission, 2003), it is used as an acidity regulator in the food industry (Linstrom & Mallard, 1998), in medicine (Gold et al., 2012), and as a raw material in the manufacture of unsaturated polyester resins (Duty & Liu, 1980).
Since the beginning of the 21st century, fumaric acid has been used to synthesize one of the first metal-organic frameworks for commercial applications (Al-MOF: A520), presenting remarkable adsorption and mechanical properties, combined with low toxicity (Gaab et al., 2012). In this context, the novel title compound was obtained during an attempt to synthesize a Cr-Fum MOF. ISSN 2056-9890 The reaction of fumaric acid and chromium(II)acetate dihydrate in the presence of dimethylamine hydrochloride resulted in the hydroamination of fumaric acid to form N,Ndimethylaspartic acid, which coordinates in a bidentate fashion to the chromium(II) ion.

Figure 2
A view along the a axis of the crystal packing of the title complex. The hydrogen bonds (Table 1) are shown as dashed lines and, for clarity, all the C-bound H atoms have been omitted.

Synthesis and crystallization
A mixture of fumaric acid (25 mg, 0.22 mmol) and dimethylamine hydrochloride (0.09 ml) dissolved in 20 ml methanol was stirred for 1 h. Chromium(II) acetate dihydrate [Cr 2 (OAc) 4 Á2H 2 O; 25.2 mg, 0.11 mmol] in 10 ml of water was added with magnetic stirring for a further 30 min. The mixture was then put in an ultrasonic bath (353 K, 45 KHz, 90 W) for 2h. The solution was then left to evaporate slowly and blue prismatic crystals were collected after two months.

Dimethylammonium bis[3-carboxy-2-(dimethylamino)propanoato-κ 2 N,O 1 ]\ chloridochromium(II) monohydrate
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.14 e Å −3 Δρ min = −0.36 e Å −3 Absolute structure: Refined as an inversion twin Absolute structure parameter: 0.422 (11) Special details 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. Refined as a 2-component inversion twin.