The silver(I) nitrate complex of the ligand N-(pyridin-2-ylmethyl)pyrazine-2-carboxamide: a metal–organic framework (MOF) structure

The reaction of silver(I) nitrate with the mono-substituted pyrazine carboxamide ligand, N-(pyridin-2-ylmethyl)-pyrazine-2-carboxamide, led to the formation of a metal-organic framework (MOF) structure.


Chemical context
We have shown recently that by using silver(I) nitrate and various tetrakis-substituted pyrazine ligands, one-, two-and three-dimensional coordination polymers can be formed (Assoumatine & Stoeckli-Evans, 2017). In the present report, the mono-substituted pyrazine carboxamide ligand, N-(pyridin-2-ylmethyl)pyrazine-2-carboxamide (L), whose crystal structure has been reported (Cati & Stoeckli-Evans, 2014), was reacted with silver(I) nitrate and led to the formation of a new compound with a metal-organic framework (MOF) structure, (I).

Structural commentary
The molecular structure of the asymmetric unit of compound (I) is illustrated in Fig. 1. Selected bond lengths and angles ISSN 2056-9890 involving the Ag1 atom are given in Table 1. Atom Ag1 is coordinated by a pyrazine N atom, N2, the pyridine N atom, N4, and two O atoms, O11 and O12, of two symmetry-related nitrate anions ( Fig. 1 and Table 1). Therefore, atom Ag1 has a fourfold N 2 O 2 coordination sphere and a distorted trigonalpyramidal geometry with a 4 parameter = 0.72 ( 4 = 1 for a perfect tetrahedral geometry, 0 for a perfect square-planar geometry; for intermediate structures, including trigonalpyramidal and seesaw, the values of 4 fall within the range of 0 to 1.0; Yang et al., 2007). Atom O13 of the nitrate anion lies above atom Ag1 with a distance Ag1Á Á ÁO13 of 2.864 (11) Å . The ligands are bridged by the silver atoms, forming -Ag-L-Ag-L-zigzag chains propagating along the a-axis direction ( Fig. 2 and Table 1). They are arranged in pairs related by a twofold screw axis (Fig. 2).

Supramolecular features
In the crystal of (I), the chains are bridged by the nitrate anions, leading to the formation of the three-dimensional framework structure (Figs. 3 and 4). The nitrate anions bridge the silver atoms in a 2 manner (Fig. 4), one of the many ways in which the nitrate anion interacts with silver atoms (Cambridge Structural Database; Groom et al., 2016). Its role here is essential in forming the MOF structure.
Within the framework, there is an N-HÁ Á ÁO hydrogen bond linking the amine group and carbonyl O atom of twofold-screw-related chains. There is also a C-HÁ Á ÁO hydrogen bond present involving a pyrazine H atom and the third O atom of the nitrate anion, O13 (Table 2). There are small voids of ca 68 Å 3 in the framework structure, equivalent to 4.8% of the volume of the unit cell.

Figure 2
A view along the c axis of the -Ag-L-Ag-L zigzag chains propagating along the a-axis direction (silver atoms are grey balls and H atoms have been omitted for clarity).

Figure 3
A view along the c axis of (I). The H atoms have been omitted for clarity, and the silver atoms and the nitrate anions are shown as balls.

Database survey
A search of the Cambridge Structural Database (Version 5.38, update February 2017; Groom et al., 2016) for the title ligand (L) gave 15 hits. These include a report of the crystal structure of (L) (Cati & Stoeckli-Evans, 2014), and that of a silver(I) BF 4 À coordination polymer (PORZOM; Hellyer et al., 2009). Here the ligand bridges the silver(I) atoms, coordinating in a bidentate (via the pyridine N atom and the carbonyl O atom) and monodentate (to a pyrazine N atom) fashion, forming zigzag chains along [010]. The chains are linked by AgÁ Á ÁAg contacts, of ca 3.32 Å , forming slabs (or metal-organic networks) lying parallel to the bc plane. The remainder of the hits in the above search are mainly first row transition metal complexes or coordination polymers.

Synthesis and crystallization
The synthesis of the ligand (L) has been described previously (Cati & Stoeckli-Evans, 2014). Ligand (L) (27 mg, 0.126 mmol) and AgNO 3 (43 mg, 0.252 mmol) were introduced into 15 ml of acetonitrile in a two-necked flask (100 ml), isolated from the light by aluminium foil. The solution was refluxed for 5 h. The resulting limpid solution was filtered and the filtrate allowed to stand at room temperature. Colourless plate-like crystals were obtained in a few days (yield 42 mg, 87%).

Figure 4
A view along the a axis of (I). The H atoms have been omitted for clarity, and the silver atoms and the nitrate anions are shown as balls. software used to prepare material for publication: SHELXL2014/6 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Poly[µ-nitrato-[µ-N-(pyridin-2-ylmethyl-κN)pyrazine-2-carboxamide-κN 4 ]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.