Metal‐Organic Frameworks: Photoreactive Frameworks

Abstract

This chapter deals with various photoreactive coordination polymers (CPs) and metal‐organic frameworks (MOFs) that undergo [2+2] cycloaddition reactions in the solid state, solid‐state structural transformations, post‐synthetic modification of surfaces creating reactive sites, radicals that are not possible by conventional synthetic routes, polymerization on the surfaces, cis‐trans isomerization of the guest molecules in the cavities as well as the dynamic behavior of the CP and MOF structures. Further the formation of these compounds by photochemical methods is also discussed. The three‐dimensional (3D) structural characterization of the products of a number of photochemical and photo‐polymerization reactions were hampered by the lack of a suitable structural tool other than single crystal X‐ray crystallography. On the other hand, most of the examples discussed in this chapter do maintain single crystals at the end of the reactions such that 3D structural elucidation is possible by single crystal X‐ray crystallography to understand the reactivity completely. A few examples have been illustrated where [2+2] cycloaddition reaction has been used to monitor the formation of ladder structures in the solid state in the absence of crystal structures.

Single-Crystal-to-Single-Crystal Transformation of Hydrogen-Bonded Triple-Stranded Ladder Coordination Polymer via Photodimerization Reaction

“…Single-crystal-to-single-crystal (SCSC) structural transformations induced by light, heat, and guest removal have received considerable interest in recent years, − particularly, light triggered SCSC transformations, which are displayed in several coordination polymers. , Since Schmidt’s postulates on topochemical reactions, , photochemists have been exploring the photochemical behavior of compounds with olefinic CC double bonds alignment that can undergo solid-state [2 + 2] cycloaddition reaction to unravel its mysteries. − Several supramolecular interactions have been investigated for this purpose, such as hydrogen bonding, halogen bonding, π–π interactions, and coordination bonding in both discrete and infinite supramolecular structures. ,,− …”

“…In the past decades, many photoreactive coordination polymers (CPs) have been synthesized and their photoreactivity has been extensively studied. ,,,, However, molecular-ladder CPs have attracted chemists’ attention due to their unique optical, , electronic, and magnetic properties. − They have several classifications based on the connectivity of metal with ligands in the rails and rungs. − Although one-dimensional ladder CP topology is uncommon, ladder CPs are considered some of the best-known assemblies to orient olefinic CC double bonds in infinite pairs for photochemical [2 + 2] cycloaddition reaction. ,− The photoreactivity of three parallel aligned CC bonds in ladder CPs was rarely studied. We have studied the remarkable photoreactivity of triple-stranded CP, [Pb 3 ­(bpe) 3 ­(O 2 C­CF 3 ) 4 ­(O 2 C­CH 3 ) 2 ], however, in which SCSC transformation was not successful due to the loss of crystallinity.…”

“…4,8,10−15 In the past decades, many photoreactive coordination polymers (CPs) have been synthesized and their photoreactivity has been extensively studied. 4,8,11,14,15 However, molecular-ladder CPs have attracted chemists' attention due to their unique optical, 16,17 electronic, and magnetic properties. 18−21 They have several classifications based on the connectivity of metal with ligands in the rails and rungs.…”

Solid‐State Photochemical [2+2] Cycloaddition Reaction of MnII Complexes

“…Following the classic work of Schmidt and co‐workers in the 1960′s, solid state [2+2] photocycloaddition reactions have been studied quite extensively in organic, coordination polymers and metal‐organic frameworks . The weak supramolecular interactions available in the crystal engineering toolbox including hydrogen and halogen bonds, π⋅⋅⋅π and C−H⋅⋅⋅π interactions, metallophilic interactions, clipping agents have been elegantly exploited to predispose the olefin pairs of the organic molecules to undergo photodimerisation in the solid state under UV light .…”

Competition Between Head-to-Head and Head-to-Tail Photocycloaddition Reaction in the Solid State: A Case Study

“…Schmidt and co-workers published their seminal work on solid state [2 + 2] photocycloaddition reaction about 50 years ago. − Later the designing principles for aligning a pair of olefin bonds extensively studied in organic crystals have been successfully extended to metal complexes, coordination polymers, and metal–organic framework structures. − In the majority of cases, symmetrical organic molecules containing olefin bonds such as 4,4′-bipyridylethylene (bpe), 1,4-bis­[2-(4-pyridyl)­ethenyl]­benzene (bpeb), 4,4′-stilbenedicarboxylate (sdb), muconate, etc. have been extensively used to study their photoreactivity in the solid state. − Similarly, unsymmetrical or terminal ligands containing olefin bonds have also been investigated. − Unlike the olefin bearing symmetrical ligands, terminal ligands such as 4-styrylpridines (4-spy) can be aligned in two different ways as shown in Figure , namely, in a head-to-head (HH) and heat-to-tail (HT) manner, giving rise to two different isomeric products.…”