Article pubs.acs.org/crystal
Making Photoreactive trans-3‑(n′‑Pyridyl)acrylic Acid (n = 2, 3) with Head-to-Tail Orientation in the Solid State by Salt Formation Goutam Kumar Kole,*,†,‡ Uma Sambasivam,† Geok Kheng Tan,† and Jagadese J. Vittal*,† †
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 Department of Chemistry and Research Institute, SRM University, Kattankulathur, Tamil Nadu 603203, India
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S Supporting Information *
ABSTRACT: This work demonstrates that the photoinert trans-3(2′-pyridyl)acrylic acid (2-PA) can be made photoreactive by salt formation with HCl, CF3CO2H, and H2SO4. All three salts undergo photodimerization in head-to-tail (HT) fashion resulting in the formation of the corresponding dimer, 2,4-bis(2′-pyridyl)-cyclobutane-1,3-dicarboxylic acid (HT-rctt-2,2′-BPCD), of which the former two salts, namely, [2-PAH]Cl·H2O and [(2-PAH)](CF3CO2) undergo single-crystal-to-single-crystal (SCSC) conversion. trans-3-(3′-Pyridyl)acrylic acid (3-PA), on the other hand, is known to be photoreactive and undergoes photodimerization in head-to-head (HH) fashion producing the dimer HH-rctt-3,3′BPCD. The HH-orientation of 3-PA can be flipped to HT by forming the ClO4− salt, which upon photodimerization produces HT-rctt-3,3′-BPCD. While HT-rctt-2,2′-BPCD exhibits isomerization in the presence of acid in solution, both the HH- and HT-rctt-3,3′-BPCD were inert under similar conditions. Our work demonstrates how the noncovalent intermolecular interactions can play a crucial role in the stereoselective synthesis and also emphasizes that the position of the nitrogen atom in the pyridyl ring is vital for the isomerization to occur in solution.
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INTRODUCTION Supramolecular or intermolecular interactions are the key foundation of designing organic and metal−organic solids.1,2 Although the intermolecular interactions are weak in general, the directional nature of some of these interactions can be exploited to anchor the relative orientation of organic molecules, and hence the overall structure can be engineered.3,4 Hydrogen bonding interaction is the most explored intermolecular interaction which is widely present in most of the organic and metal−organic solids in various ways.5,6 By incorporating complementary functional groups, hydrogen bonding can be modulated into a powerful tool to design crystal packing and solid state organic synthesis.7−11 The crystal engineering community has devoted considerable attention to make photoreactive organic cocrystals, salts, coordination compounds, and host−guest systems to undergo the solid state [2 + 2] cycloaddition reaction.12−16 In these compounds, the CC bond pairs in the organic moieties are brought into parallel arrangement within the required distance (usually
