Nitrate Ion Assisted Argentophilic Interactions as a Template for Solid State [2+2] Photodimerization of Pyridyl Acrylic Acid, Its Methyl Ester, and Acryl Amide

Ag center dot center dot center dot Ag interactions were shown to template [2 + 2] photochemical reactions of unsymmetrically substituted olefin molecules, namely 4-pyridyl acrylic acid (I), 4-pyridyl acryl amide (2), and methyl ester of 4-pyridyl acrylic acid (3) in their Ag(I) complexes [Ag(1)(2)(NO3)]center dot MeOH (4); [Ag(2)(2)(NO3)] (5); and [Ag(3)(2)(NO3)]center dot MeOH (6). Nitrate ions were found to bridge these Ag center dot center dot center dot Ag interactions in two ways: as a discrete dimer in 4 and 5 and as a zigzag 1D-polymer in the case of 6. Irradiation of these complexes in UV/sunlight produced respective head-to-head dimers in nearly 100% yields, as supported by H-1 NMR spectroscopy. In the case of 5, the transformation was shown to occur in single crystal to single crystal fashion by determining the crystal structure of partially irradiated materials of 5. Further, we have also found that the irradiation of mechanically grounded samples of AgNO3 with 2 or 3 produces a similar [2 + 2] reaction, to result in respective head-to-head dimers in good yields.