Crystal structure of bis(1,3-diaminopropane-κ2 N,N′)bis[2-(4-nitrophenyl)acetato-κO]cadmium

In a cadmium complex incorporating 1,3-diaminopropane and nitrophenylacetate ligands, the CdII atom is located on a center of symmetry with an overall octahedral coordination environment. Both intra- and intermolecular interactions occur between the amino and acetate groups, leading to a layered structure.


Chemical context
The motivation for this study is based on the desire to expand the crystal engineering aspect of 1,3-diamino propane and carboxylate ligands and enhance their applications in hostguest chemistry (Sundberg et al., 2001). It is known that the 1,3-diaminopropane ligand behaves as a strong chelator and forms a stable six-membered ring in its metal complexes as well as being a good hydrogen-bond donor due to the existence of the amino groups (Sundberg et al., 2001). In contrast, the 2-(4-nitrophenyl)acetate ligand has the potential to act as a linker and can also act as a good hydrogen-bond acceptor due to the four oxygen atoms it contains. Combination of these ligands in a single system has the potential to construct hydrogen-bond-directed supramolecular networks. Herein, we report the synthesis and structure of the title compound, [Cd(C 8 H 6 NO 4 ) 2 (C 3 H 10 N 2 ) 2 ], which displays such a hydrogenbond-directed structure. ISSN 2056-9890

Structural commentary
As shown in Fig. 1, the Cd II atom is located on a center of symmetry. Therefore the asymmetric unit consist of half of the molecule. The Cd II atom is octahedrally coordinated by four N atoms from two diamino propane ligands and two O atoms of monodentate acetate groups from two nitrophenyl-acetate ligands. The diamino propane ligand shows a chelating coordination behavior and displays a chair conformation in the equatorial direction. This kind of coordination mode was also found in other similar complexes (Roberts et al., 2015;Sundberg & Uggla, 1997Sundberg et al., 2001), although the ligand has also been used as a linker of two metal atoms (Sheng et al., 2014). The nitro group is slightly twisted out of the aromatic plane, with a dihedral angle of 3.6 (3) between the two leastsquares planes. A weak intramolecular hydrogen bond of the type N-HÁ Á ÁO involving one of the amino N atoms of the diaminopropane ligand and the non-coordinating carboxylate O atom of the nitrophenylacetate ligand is evident in the structure at a distance of 3.029 (3) Å (Table 1).

Supramolecular features
Somewhat weaker intermolecular N-HÁ Á ÁO interactions involving the same types of donor and acceptor groups occur between neighboring molecules (Table 1) and lead to a layered arrangement of the molecules parallel to the bc plane (Fig. 2). It should be noted that one of the hydrogen atoms (H1B) of the amino group N1 has no acceptor group in its vicinity; the shortest donorÁ Á Áacceptor distance of N1-H1BÁ Á ÁO2 = 3.868 Å seems to be too long for a significant interaction. Several other weak intermolecular hydrogenbonding interactions of the C-HÁ Á ÁO type also exist in the structure involving the O atoms of nitro groups and neighboring C-H groups. The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Non-labelled atoms are generated by the symmetry code Àx + 1, Ày + 1, Àz + 2. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A packing diagram of the title compound. The light-blue dotted lines indicate intramolecular hydrogen-bonding interactions, as well as intralayer interactions involving the nitro groups of adjacent molecules. A weak N-HÁ Á ÁO interlayer interaction also exists at 3.149 (3) Å , linking the layers (see Table 1 for details).

Synthesis and crystallization
0.2 mmol (36.7 mg) of anhydrous CdCl 2 , 0.4 mmol (29.7 mg) of 1,3-diaminopropane, and 0.4 mmol (72.5 mg) of 4-nitrophenylacetic acid were added to 2 ml of methanol in a 5 ml beaker. The sample was covered with aluminum foil containing several small vent holes and left for a week to evaporate. The slow evaporation method was used to crys-tallize a colorless mononuclear species and crystals were gathered for X-ray crystallographic analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions and allowed to ride during subsequent refinement, with U iso (H) = 1.2U eq (C) and C-H distances of 0.93 Å for aromatic hydrogen atoms, U iso (H) = 1.2U eq (C) and C-H distances of 0.97 Å for methylene hydrogen atoms, and U iso (H) = 1.2U eq (N) and N-H distances of 0.90 Å for amino hydrogen atoms.    (Bourhis et al., 2015); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Bis(1,3-diaminopropane-κ 2 N,N′)bis[2-(4-nitrophenyl)acetato-κO]cadmium
Crystal data Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0012 (2) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.