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

The title ligand, C(18)H(16)N(6)O(2)·2H(2)O (L1) [N (2),N (3)-bis­(pyridin-4-ylmeth­yl)pyrazine-2,3-dicarboxamide], crystallized as a dihydrate. The mol­ecule 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 intra­molecular N—H⋯N(pyrazine) hydrogen bond present, forming an S(5) ring motif. In the crystal, adjacent mol­ecules are linked by N—H⋯O(carboxamide) hydrogen bonds, forming a chain along [001]. A chain of hydrogen-bonded water mol­ecules is linked to the chain of (L1) mol­ecules 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 supra­molecular structure. The reaction of ligand (L1) with silver(I) nitrate led to the formation of a new three-dimensional coordination polymer, {[Ag(C(18)H(16)N(6)O(2))]NO(3)}(n), poly[[[μ(4)-N (2),N (3)-bis­(pyridin-4-ylmeth­yl)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 mol­ecule and half a positionally disordered nitrate anion located about a twofold rotation axis. The full mol­ecule of the ligand is generated by twofold rotational symmetry, with this twofold axis bis­ecting the C(ar)—C(ar) 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 mol­ecule. Each silver ion is coordinated by two pyridine N atoms and by two carboxamide O atoms of neighbouring mol­ecules, hence forming a three-dimensional framework. The nitrate anion is linked to the framework by N—H⋯O and C—H⋯O hydrogen bonds.