Crystal structure of (1,3-thiazole-2-carboxylato-κN)(1,3-thiazole-2-carboxylic acid-κN)silver(I)

The AgI ion is coordinated by two heterocyclic N atoms from two ligands in a linear configuration, forming a discrete coordination complex. There is an O—H⋯O hydrogen bond between 2-tza− and 2tzaH of adjacent complexes. The hydrogen atom is shared between the two oxygen atoms.


Chemical context
1,3-Thiazoles have been known for over a century and many of their derivatives exhibit potential applications, particularly in drug design and biological activity (Ayati et al., 2015;Kashyap et al., 2012). The thiazolecarboxylic acids have also received attention as ligands in complexes of the first-row transition metals. This is due to the co-presence of the heterocyclic ring and the carboxyl group providing various coordination modes (Frija et al., 2016). They also favour the assembly of supramolecular architectures by establishing a variety of noncovalent interactions e.g. hydrogen bonding andstacking interactions (Desiraju, 2002;Sherrington & Taskinen, 2001;Blake et al., 1999). Recently, we reported the syntheses and structural features of Co II , Ni II , and Cu II complexes with thiazole-4-carboxylate (Meundaeng et al., 2016) and thiazole-5-carboxylate (Meundaeng et al., 2017). Herein we report the synthesis and crystal structure of the Ag I complex with thiazole-2-carboxylic acid (2-tza). ISSN 2056-9890

Structural commentary
The monomeric complex of the title compound crystallizes in the monoclinic space group P2 1 /c. The asymmetric unit contains one Ag I ion and one 2-tza ligand which is formally 2-tza(H) 1/2 . The whole molecular structure can be generated by an inversion centre; the Ag I atom is located at the 2a Wyckoff position (1) (Fig. 1). The Ag I centre shows a linear coordination with two 2-tza ligands coordinating through the heterocyclic N atoms with an Ag-N bond length of 2.1463 (14) Å . Statistically one of these ligands has an appended carboxylic acid and the other a carboxylate. A rather long AgÁ Á ÁO2 interaction is also observed with the distance of 2.8401 (13) Å . This is significantly larger than the mean value [2.54 (11) Å ] of the AgÁ Á ÁO C distances in the Cambridge Database (version 5.37 up to October 2018;Groom et al., 2016; 23 hits, silver bound by two nitrogen atoms, AgÁ Á ÁO C distance recorded) and suggests that the interaction between the carbonyl and the silver atom is very weak. No interactions between the Ag centres are observed.

Supramolecular features
In order to balance charge in this structure, the 2-tza ligand must be half protonated but we see no evidence for crystallographic ordering of the hydrogen position. In late stages of  Table 1 Hydrogen-bond geometry (Å , ).
refinement, a maximum of electron density in the difference-Fourier map was present located 0.897 Å from the atom O2. This was modelled as a half occupied hydrogen atom. Thus, the overall composition is Ag + (2-Htza)(2-tza À ). The carboxylate is located close to a second symmetry-equivalent carboxylate generated by the symmetry operation 1 À x, Ày, 1 À z. Statistically, one of these two groups is protonated. The close approach facilitates the formation of a linear hydrogen bond between them (Table 1) and the OÁ Á ÁO distance of 2.470 (3) Å strongly suggests that there is a hydrogen bond. Strangely, it is not the case that the O2-H2 distance is half the O2Á Á ÁO2 i distance as is sometimes observed in similar systems (Leiva et al., 1999;Deloume et al., 1977). The partially occupied H2 atom is clearly identified from a Fourier map at the closer distance to the atom O2. Furthermore, the carboxyl O1 atom serves as a hydrogen-bonding acceptor with the heterocyclic H3 atom (Csp 2 -HÁ Á ÁC O) of an adjacent discrete molecule (  (Fig. 2b). These columns are further linked via C-HÁ Á Á interactions between the thiazole rings (Table 1), leading to the formation of a threedimensional supramolecular architecture (Fig. 3).  (Rossin et al., 2011) and Co II , Ni II , Cu II complexes (Meundaeng et al., 2016) and one with Sn IV (Gao et al., 2016); and two reports of thiazole-5-carboxylic acid (5-tza) complexes each with Cu II (Rossin et al., 2014;Meundaeng et al., 2017

Figure 3
View of supramolecular interactions; hydrogen bonds between the discrete units (red dashed lines), AgÁ Á ÁO interactions between adjacent one-dimensional tapes (black dashed lines) and C-HÁ Á Á interactions between adjacent columns (purple dashed lines).

(1,3-Thiazole-2-carboxylato-κN)(1,3-thiazole-2-carboxylic acid-κN)silver(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.