Solid-State Structural Transformation in Zn(II) Metal–Organic Frameworks in a Single-Crystal-to-Single-Crystal Fashion

Abstract

Solid-state structural transformation is an interesting methodology used to prepare various metal–organic frameworks (MOFs) that are challenging to prepare in direct synthetic procedures. On the other hand, solid-state [2 + 2] photoreactions are distinctive methodologies used for light-driven solid-state transformations. Meanwhile, most of these photoreactions explored are quantitative in nature, in addition to them being stereo-selective and regio-specific in manner. In this work, we successfully synthesized two photoreactive novel binuclear Zn(II) MOFs, [Zn2(spy)2(tdc)2] (1) and [Zn2(spy)4(tdc)2] (2) (where spy = 4-styrylpyridine and tdc = 2,5-thiophenedicarboxylate) with different secondary building units. Both MOFs are interdigitated in nature and are 2D and 1D frameworks, respectively. Both the compounds showed 100% and 50% photoreaction upon UV irradiation, as estimated from the structural analysis for 1 and 2, respectively. This light-driven transformation resulted in the formation of 3D, [Zn2(rctt-ppcb)(tdc)2] (3), and 2D, [Zn2(spy)2(rctt-ppcb)(tdc)2] (4) (where rctt = regio, cis, trans, trans; ppcb = 1,3-bis(4′-pyridyl)-2,4-bis(phenyl)cyclobutane), respectively. These solid-state structural transformations were observed as an interesting post-synthetic modification. Overall, we successfully transformed novel lower-dimensional frameworks into higher-dimensional materials using a solid-state [2 + 2] photocycloaddition reaction.