Crystal structure of a pyrazine-2,3-dicarboxamide ligand and of its silver(I) nitrate complex, a three-dimensional coordination polymer.

The title ligand, C18H16N6O2·2H2O (L1) [N(2),N(3)-bis-(pyridin-4-ylmeth-yl)pyrazine-2,3-dicarboxamide], crystallized as a dihydrate. The mol-ecule is U-shaped with the carboxamide groups being cis to one another, making a dihedral angle of 81.6 (5)°. The terminal pyridine rings are inclined to one another by 58.5 (4)°. There is an intra-molecular N-H⋯Npyrazine hydrogen bond present, forming an S(5) ring motif. In the crystal, adjacent mol-ecules are linked by N-H⋯Ocarboxamide hydrogen bonds, forming a chain along [001]. A chain of hydrogen-bonded water mol-ecules is linked to the chain of (L1) mol-ecules by O-H⋯N hydrogen bonds, forming columns propagating along the c axis. The columns are linked by C-H⋯O and C-H⋯N hydrogen bonds, forming a three-dimensional supra-molecular structure. The reaction of ligand (L1) with silver(I) nitrate led to the formation of a new three-dimensional coordination polymer, {[Ag(C18H16N6O2)]NO3} n , poly[[[μ4-N(2),N(3)-bis-(pyridin-4-ylmeth-yl)pyrazine-2,3-dicarboxamide]-silver(I)] nitrate] (I). The asymmetric unit is composed of half of one silver ion, located on a twofold rotation axis, half a ligand mol-ecule and half a positionally disordered nitrate anion located about a twofold rotation axis. The full mol-ecule of the ligand is generated by twofold rotational symmetry, with this twofold axis bis-ecting the Car-Car bonds of the pyrazine ring and the Ag-Ag bond. The carboxamide groups are now trans to one another, making a dihedral angle of 65.8 (4)°. The two terminal pyridine rings are inclined to one another by 6.6 (3)°. Two ligands wrap around an Ag-Ag bond of 3.1638 (11) Å, forming a figure-of-eight-shaped complex mol-ecule. Each silver ion is coordinated by two pyridine N atoms and by two carboxamide O atoms of neighbouring mol-ecules, hence forming a three-dimensional framework. The nitrate anion is linked to the framework by N-H⋯O and C-H⋯O hydrogen bonds.