New Ag(I) coordination polymers of 2,6-pyridine-dicarboxamide: In situ ligand formation and a unique secondary building unit

The hydrothermal reactions of 2,6-dicyanopyridine with AgX (X = NO3, ClO4, BF4) yielded intriguing network structures. The syntheses involve in situ generation of 2,6-pyridine-dicarboxamide (pcam), forming [Ag(pcam)2X]n·mH2O [X = NO3 (1), m = 0; BF4 (2), m = 1; ClO4 (3), m = 1]. These solids contain an unprecedented SBU, involving simultaneous Agsingle bondO bonds/interactions and NH···O hydrogen bonding. The SBUs combine to form 2D square grids, which are stacked orderly by weak Ag···O contacts and π–π stacking interactions, forming 3D networks with infinite 1D channels, in which anions are residing. Weak Ag···O interactions play a key role in these solids and they display dynamic behaviors in solution as demonstrated by NMR spectroscopy and ESI-MS. The importance of the supramolecular synthons in the SBU was demonstrated by varying the structure of the organic tecton. Attempts to prepare similar network structures based on stronger OH···O interactions from pyridine-2,6-dicarboxylic acid (H2dipic) afforded a topologically different 2D coordination polymer.