Crystal structure of silver [(propane-1,3-diyldinitrilo-κ2 N,N′)tetraacetato-κ4 O,O′,O′′,O′′′]chromate(III) from synchrotron X-ray data

In the title complex, the Cr3+ ion is coordinated by the four O and two N atoms of the 1,3-pdta ligand, displaying a distorted octahedral geometry. The Ag+ cation is surrounded by six O atoms from neighboring 1,3-pdta groups and water molecules.


Structural commentary
This is another example of a [Cr(1,3-pdta)] À anion but with a different cation. The crystal structure of the title compound is isotypic with Na[M(1,3-pdta)]Á3H 2 O (M = Fe, Cr or Rh; Okamoto et al., 1990;Herak et al., 1984) but it belongs to the orthorhombic space group P2 1 2 1 2 1 compared with the monoclinic space group P2 1 /n of Li[Fe(1,3-pdta)]Á3H 2 O (Yamamoto et al., 1988) and orthorhombic space group B22 1 2 of K[Co(1,3pdta)]Á2H 2 O (Nagao et al., 1972). The structural analysis shows that the propane-1,3-diyldinitrilotetraacetate anion is coordinated octahedrally by the Cr metal center through four O and two N atoms. An ellipsoid plot of title complex showing the atomic numbering is given in Fig. 1. The Cr-O bond distances differ slightly, the mean equatorial and axial distances being 1.9672 (15) and 1.9544 (15) Å , respectively. The cis angles at the Cr III ion range from 81.66 (6) to 99.41 (6) and the trans angles are 173.07 (7), 175.01 (6) and 176.04 (7) . The sixmembered propane-1,3-diamine T ring (Fig. 1) adopts a flexible twist-boat conformation. The R rings are nearly planar and are in an envelope conformation. The G rings are much more puckered and are halfway between an envelope and a twist conformation. The Cr-O bond distances are greater in the G rings than in the R rings, and the average Cr-N bond length of 2.0727 (17) (Herak et al., 1984).

Figure 2
Crystal packing of Ag

Synthesis and physical measurements
All chemicals were reagent-grade materials and were used without further purification. The UV-Vis absorption spectrum was recorded with a Cary 5000 UV-Vis-NIR Spectrophotometer. The FT-IR spectrum was obtained from a KBr pellet with a JASCO 460 plus series FT-IR spectrometer. Analyses for C, H, N were performed on a Carlo Erba 1108 Elemental Vario EL analyser. The precursor salt, Na[Cr(1,3pdta)]Á3H 2 O was prepared as described previously (Weyh & Hamm, 1968;Herak et al., 1984). The sodium salt (0.20 g) was dissolved in 15 mL of water at 323 K and added to 3 mL of water containing 0.5 g of AgNO 3 .

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.97 Å with U iso (H) = 1.2U eq (C). O-bound H atoms were assigned based on a difference-Fourier map, and were refined with distance restraints of 0.88 (2) Å (using DFIX and DANG commands), and U iso (H) = 1.2U eq (O).

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.