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The title ligand, C 18 H 16 N 6 O 2 ·2H 2 O ( 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⋯N pyrazine hydrogen bond present, forming an S (5) ring motif. In the crystal, adjacent mol-ecules are linked by N-H⋯O carboxamide 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(C 18 H 16 N 6 O 2 )]NO 3 }  n  , poly[[[μ 4 - 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 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 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.

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