Crystal structure of poly[diaquabis(μ5-benzene-1,3-dicarboxylato)(N,N-dimethylformamide)cadmium(II)disodium(I)]

A novel three-dimensional bimetallic CdII–NaI metal–organic framework has been synthesized and the X-ray structure has been reported.


Structural commentary
The title compound (I) crystallizes in the tetragonal crystal system with polar P4 3 space group. The asymmetric unit of (I) consists of one Cd II ion, two crystallographically independent Na(I) ions, two 1,3-bdc ligands, two coordinated water molecules and one DMF molecules, as shown in Fig. 1. Each Cd II ion is coordinated by seven carboxylate oxygen atoms from four different 1,3-bdc ligands with the Cd-O bond distances range between 2.301 (3) and 2.555 (3) Å (Table 1). The Na1 ion is surrounded by three carboxylate oxygen atoms of three different 1,3-bdc ligands, one oxygen atom from a water molecule, and one DMF molecule with the Na-O bond distances ranging between 2.304 (7) and 2.498 (11) Å , while the Na2 ion adopts a five-coordinate [4 + 1] coordination with four oxygen atoms from three different 1,3-bdc ligands and one oxygen atom from a water molecule. The Na-O bond distances are in the range 2.275 (5) to 2.354 (8) Å . Fig. 2 shows the coordination modes of the 1,3-bdc ligand in compound (I). The 1,3-bdc molecule is fully deprotonated and coordinated to the Cd II and Na I ions in a 5 -coordination mode, creating a one-dimensional heterobimetallic chain running parallel to the c axis, Fig. 3 Symmetry codes: (i) x; y À 1; z; (ii) x À 1; y; z; (iii) Ày þ 1; x; z À 1 4 ; (iv) y À 1; Àx; z þ 1 4 ; (v) y; Àx þ 1; z þ 1 4 .

Figure 1
Asymmetric unit of (I) with the atomic-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
through the 1,3-bdc ligands in the a-and b-axis directions, generating a three-dimensional framework structure as shown in Fig. 4. The coordinated water and DMF molecules adopt a monodentate coordination mode and serve as a terminal pendant ligand pointing inside the channels.

Supramolecular features
In the crystal of (I), classical O-HÁ Á ÁO hydrogen bonds and aromaticstacking interactions are observed and these interactions presumably help to stabilize the frameworks. All water molecules are shown to act as O-HÁ Á ÁO hydrogenbond donors towards the carboxylate groups of the 1,3-bdc ligands ( Table 2). Thestacking interactions are between symmetry-related aromatic rings of the 1,3-bdc ligands with a Cg1Á Á ÁCg2 i distance of 3.588 (3) Å and a dihedral angle of 3.8 (4) [Cg1 and Cg2 are the centroids of the C1-C6 and C9-C14 rings, respectively; symmetry code: (i) -y, x, z -1/4].

Figure 3
Perspective view along the crystallographic c axis of (a) the threedimensional framework of (I) (the coordination polyhedra for Cd II and Na I are pink and green, respectively) and (b) helical chain-like structure of the Cd-Na clusters (dark blue = Cd, blue = Na and red = O).

Figure 4
Perspective view of the three-dimensional framework of (I) (the coordination polyhedra for Cd II and Na I are pink and green, respectively). All hydrogen atoms are omitted for clarity.

Synthesis and crystallization
A mixture solution of 1,3-bdcH 2 (1.0 mmol) and NaOH (2.0 mmol) in 10 mL of distilled water was slowly dropped to a methanolic solution (10 ml) of Cd(NO 3 ) 2 Á4H 2 O (1.0 mmol). The reaction mixture was stirred at 333 K for 30 min and allowed to cool to room temperature and then filtered. The filtrate was allowed to stand to slowly evaporate at ambient temperature. Colorless block-shaped crystals suitable for single crystal X-ray diffraction were obtained after three days (76% yield based on Cd).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All hydrogen atoms except those of water molecules were generated geometrically and refined isotropically using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). The coordinated DMF molecule was found to be disordered with two sets of sites with a refined occupancy ratio of 0.382 (10) and 0.618 (10).

Poly[diaquabis(µ 5 -benzene-1,3-dicarboxylato)(N,N-dimethylformamide)cadmium(II)disodium(I)]
Crystal data  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.