Crystal structure of a mixed-ligand silver(I) complex of the non-steroidal anti-inflammatory drug diclofenac and pyrimidine

The coordination polymeric silver(I)–diclofenac complex including pyrimidine is based on a centrosymmetric carboxylate O:O′-bridged dinuclear unit which is extended through N-atom donors of the pyrimidine ligand into a two-dimensional layered structure


Chemical context
The design of coordination polymers based on silver(I) has been studied extensively in recent years because of their various structural topologies as well as photoluminescent properties and antimicrobial activity. These studies have shown that short AgÁ Á ÁAg separations are one of the most important factors for the manifestation of such properties [Yam & Lo, 1999;Pyykkö et al., 1997;Wang & Cohen, 2009;Zhang et al., 2009, Njogu et al., 2015Nomiya et al., 2000]. On the other hand, it is known that to construct extended coordination networks with polynuclear metal-based structures, ligands of various binding sites and shapes have to be taken into account. At this stage, confidence in accomplishing this goal is based upon the sophisticated selection and utilization of suitable multifunctional organic ligands with certain features, such as being a multiple donor and having versatile bonding modes or the ability to take part in hydrogen bonding. Aromatic carboxylate derivatives have therefore been of interest in coordination and supramolecular chemistry.

Figure 2
A view of the centrosymmetric caboxylate-bridged dinuclear [Ag 2 (dicl) 2 ] unit in (I  (Addison et al., 1984). As illustrated in Fig. 3, in the title complex, the pym ligand acts as a 2 -N,N 1 -bridging ligand between neighboring [Ag 2 (COO) 2 ] units, leading to the formation of a twodimensional coordination polymer, extending along (100) (Fig. 4). In other words, [Ag 2 (COO) 2 ] units, which comprise eight-membered rings, can be defined as the nodes of the structure. Connection of the four different pym ligands to these nodes provides continuity of the structure (Fig. 4).

Figure 5
The packing of (I) in the unit cell viewed along the b axis.

Synthesis and crystallization
All reactions were performed with commercially available reagents and used without further purification. Solid sodium 2-(2,6-dicholoroanilino)phenylacetate (Nadicl) (0.32 g, 1 mmol) and pyrimidine (0.08 g, 1 mol) were added to an aqueous solution (10 cm 3 ) of AgNO 3 (0.17 g, 1 mmol) with stirring. A white suspension with a white precipitate formed and the addition of acetonitrile (10 cm 3 ) to this resulted in a clear solution which was left to stand for slow evaporation in darkness at room temperature. Single crystals of (I) suitable for X-ray analysis were obtained within a few days.

Spectroscopy
The infrared spectrum was obtained using a Perkin Elmer Spectrum Two FTIR with a diamond Attenuated Total Reflectance attachment (ATR) in the frequency range 4000-600 cm À1 . The sample was placed on the ATR crystal and pressure exerted by screwing the pressure clamp onto the sample to ensure maximum contact with the ATR crystal. The characteristic absorption bands of Nadicl and the title complex are listed in Table 3. The spectrum is deposited as a supplementary Fig. S1.
The characteristic absorption band in the FT-IR spectra of the carboxylate complexes is the asymmetric ( as ) and symmetric ( s ) vibrations of the carboxylate group. The difference between the asymmetric and symmetric carboxylate stretching [Á = as (COO À )s (COO À )] is often used to correlate the infrared spectra of metal carboxylate structures. When Á < 200 cm À1 , the carboxylate groups of the complexes can be considered bidentate (Azó car et al., 2013). The value of Á is calculated as 183 cm À1 for 1. Based on the above-mentioned points, it is suggested that carboxylate groups in the complex exhibit a bidentate coordination mode, as revealed by the structural analysis. Table 3 Selected comparative IR spectral data for Nadicl and the dicl ligand in (I).

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.