Crystal structure of hexaaquachromium(III) dimethylformamidium bis(4-hydroxypyridine-2,6-dicarboxylate), [Cr(H2O)6][C3H8NO][C7H3NO5]2

Abstract

Source of materialAm ixture of chromium(III) nitrate (0.03 mmol, 0.013 g), and chelidamic acid (0.11 mmol, 0.02 g) were dissolved in a10mL water. After slow adding 1mLethanol and 5mLDMF, adjusting pH to 5, stirring for about 4h,the mixed solution was filtered. The filtrate was allowed to stand at room temperature. Green prismshaped crystals that are stable in air were obtained over aperiod of 10 d. Elemental analysis -found: C, 34.28 %; H, 3.73 %; N, 7.10 %; calculated for C 17H25CrN3O17:C,34.23 %; H, 3.69 %; N, 7.04 %. Experimental detailsAll the Hatoms of water molecules were found in difference Fourier map and refined with U iso(H) =1.5 Ueq(O). Other Hatoms (except for O25) were all placed in calculated positions and allowed to ride on its parent atoms with DiscussionThe asymmetrical unit of the title crystal structure consists of one Cr atom, two discret chelidamic acid ligands, six coordinating water molecules and one discret N,N-dimethylformamide (DMF) molecules. The Cr(III) ion is coordinated by six water molecules to form adistorted octahedron. The equatorial plane consists of four oxygen atoms (O3W, O4W, O5W and O6W), while the axial positions are occupied by another two water oxygenss (O1W and O2W). The bond lengths of Cr-Or ange from 1.934(2) to 1.981(2) Å,which falls in the normal range reported for the chromium complexes in the literature [1][2][3][4]. The discret chromium complexes in the title compound are linked by the hydrogen bonds between O1W and O11, O2W and O25, O1 and O2W, O3W and O13, O4W and O14, O5W and O24, O6W and O23 to form an infinite chain along the [001]. The neighboring chains are connected into alayer through the hydrogen bonds between O1 and O1W, O15 and O25. These layers are in turn inter-linked through av ery complex hydrogen bonding network involving water molecules and oxygen atoms from the chelidamic acid ligands to form a3Dsupramolecular network. The chromium atoms and the chelidamate anions show oxidation states of +3 and -2, respectively. Thus, for charge neutralization, the discret DMF molecule should protonated through locating the Hatom on N3 or O1 atoms. But we could not locate the hydrogen atoms in the difference Fourier map.