Crystal structure of poly[[[μ4-3-(1,2,4-triazol-4-yl)adamantane-1-carboxylato-κ5 N 1:N 2:O 1:O 1,O 1′]silver(I)] dihydrate]

The title AgI compound based on 3-(1,2,4-triazol-4-yl)adamantane-1-carboxylate (tr-ad-COO−) is a three-dimensional coordination framework with channels along the c-axis direction. Hydrogen bonding between water molecules of crystallization and carboxylate groups is realised in form of right- and left-handed helical motifs.


Chemical context
Organic ligands, which contain two different functional groups, such as azole and carboxylic groups, attract attention in the context of the construction of unusual metal-organic frameworks (MOFs) including heterometallic architectures (Guillerm et al. 2014). Each ligand function is intended to introduce its coordination ability towards a metal center forming secondary building units (SBUs) based on its peculiarities. For instance, 1,2,4-triazoles (tr) typically serve as short N,N-bridges between two metal ions resulting in polynuclear units and chains (Wang et al. 2007, Murdock & Jenkins 2014. In contrast, carboxylate groups offer a much broader variety of coordination modes: mono-, chelate-, bridging-and their combinations; and the number of connected metal ions may differ from one to four (Sun et al. 2004;Lu et al. 2014). As shown by Lincke et al. (2011Lincke et al. ( , 2012, 1,2,4-triazolecarboxylate ligands are good candidates for the construction of microporous MOFs suitable for gas sorption and separation. Considering the heterofunctional tr/COO ligands, there are two possible roles for them to play. First, the 'separate' role, where tr is responsible for di-, tri-or tetranuclear cluster formation, whereas the COO À group only occupies terminal (non-bridging) positions (Handke et al. 2014) or it can be involved in the separate coordination to metal centers. In this context, Chen et al. (2011) used 1,2,4-triazolyl isophthalate as a ligand in the synthesis of a series of Ag I -Ln III heterometallic coordination polymers. Second, in the 'cooperative' role, tr/ COO serves as a heteroleptic bridge between the metal centers (Vasylevs'kyy et al. 2015).

Structural commentary
The title compound I crystallizes in the orthorhombic system with the uncommon space group C222 1 . The asymmetric unit contains one Ag I cation, one organic ligand and three distinct water molecules of crystallization, one of which (O5) is disordered over two adjacent sites (Fig. 1). The O3 water molecule is situated on a crystallographic twofold axis passing through the O atom, while the O4 water molecule is statistically disordered over two positions, both possessing an occupancy factor of 0.5. Thus, in the asymmetric unit, the total atom content sums up to two water molecules. The 1,2,4triazole functional group is coordinated by two Ag I centers as a 2 -N,N bridge and the carboxylate group connects two Ag I centers in a chelating, bridging mode ( 2 -2 : 1 ), supporting the formation of sinusoidal chains with a periodicity of 13 Å .
In the case of compound I an unusual situation with alternation of double triazoles and double carboxylate bridges within the chain is observed. Thus, the tr-ad-COO À ligands act in a deprotonated form adopting a 4 -coordination modes ( Fig. 2) that yields a three-dimensional tetragonal pattern with open channels along the c-axis direction (Fig. 3).  Projection on the bc plane showing the interconnection of sinusoidal Ag I coordination chains by means of tr-ad-COO À organic ligands into a threedimensional framework.

Figure 1
Fragment of the crystal structure of I. The independent part of the structure is indicated with black bonds and displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1 2 À x, À 1 2 + y, View of the channels along the c axis in the structure of I.

Supramolecular features
The water guest molecules inside the [001] channels are responsible for the extended hydrogen-bonding network ( Table 2). Together with the -COO À groups, they are organized into two types of helices along the c axis -smaller righthanded (A in Fig. 4) and bigger left-handed (B in Fig. 4). In addition, weak C-H (triazole) Á Á ÁO1 (COO) and C-H (triazole)Á Á ÁO4(water) contacts are observed. The packig is shown in Fig. 5.

Figure 5
The packing of the right-and left-handed helices in the crystal structure of I (top view). Adamantyl fragments are omitted for clarity.
with C-H = 0.94 Å (triazole); C-H = 0.98 Å (adamantane CH 2 ); C-H = 0.99 Å (adamantane CH) and with U iso (H) = 1.2U eq (C). OH hydrogen atoms were located and then refined with O-H = 0.85 Å (H 2 O) and with U iso (H) = 1.5U eq (O). For one of the disordered water molecules, the H atoms were not located.   , 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012).  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.