Solid‐State Photochemical [2+2] Cycloaddition Reaction of Mn^II Complexes

Abstract

Three Mn II complexes have been synthesized under similare xperimental conditions. Of these [Mn 2 (benzoate) 4 (L) 2 ]( whereL = 4-styrylpyridine or 4spy, 1 and 2-fluoro-4'-styrylpyridineo r2 F-4spy, 3)a re paddlewheel complexes, but crystallized in different space groups.W hereas [Mn 2 (benzoate) 4 (3F-4spy) 4 ]( 3F-4spy = 3-fluoro-4'-styrylpyridine), 4 is ad inuclearc omplex having different stoichiometry from 1 and 3 with two pairs of 3F-4spy ligandsalignedi n face-to-face manner.A ni rreversible phase transition occurs from the space group P2 1 /c to C2/c when 1 was heated up to 125 8Ct o2 in as ingle-crystal-to-single-crystal fashion or when ground 1 to powder. 2 is isomorphousa nd isostruc-tural to 3.C omplimentary p-p interactions in head-to-tail alignment of the styrylpyridine ligands furnishes 1D aggregates in 1-3 which are congenial to undergo [2+ +2] cycloaddition reaction under UV light. Whereas, face-to-facea lignment of the 4spy pairs in 4 is expected to provide ah eadto-head photoproduct. All theM n II complexes are indeed found to be photoreactive.T oo ur surprise, contrary to their Zn II analogues, 2 and 3 were not found to be photosalient. The percentage volumee xpansiond uring the photoreaction as determined from the density measurements, was found to be too low (3.2 and4 .6 %r espectively for 2 and 3)t o have this behavior.1 HNMR spectroscopy has also confirmed the ratios between the ligands in these complexes.

Cocrystal Strategy to Harmonize the Photochemical Reactivity of Styrylquinolines and the Photoactuation Performance of the Molecular Crystals

“…As for the olefin-based molecular crystals, [2 + 2] cycloaddition between adjacent C�C double bonds would trigger the macroscopic mechanical motions. Although styrylpyridine is one of the widely studied building blocks in photomechanical systems, 23,24 the distance between adjacent C�C double bonds was often greater than 4.2 Å in crystals. 20,25 Accordingly, the template-assisted method has been employed for the prearrangement of styrylpyridine units in crystals so as to make the packing meet Schmidt's criteria.…”

“…As for the olefin-based molecular crystals, [2 + 2] cycloaddition between adjacent CC double bonds would trigger the macroscopic mechanical motions. Although styrylpyridine is one of the widely studied building blocks in photomechanical systems, , the distance between adjacent CC double bonds was often greater than 4.2 Å in crystals. , Accordingly, the template-assisted method has been employed for the prearrangement of styrylpyridine units in crystals so as to make the packing meet Schmidt’s criteria. , Vittal and Rath presented the photosalient behavior of the crystal based on the complexes where the distorted octahedral Pb­(II) center is coordinated to the N atom in styrylpyridine derivatives and the strain is generated during the photo-induced [2 + 2] cycloaddition reaction. , MacGillivray et al reported the supramolecular alignment between resorcinol and styrylpyridine via multiple H-bonds of O–H···N so as to realize the photochemical reaction-powered mechanical response of the crystals . Besides, much effort is also made to optimize the olefin geometry, such as cocrystal engineering.…”

Photomechanical effect in Zn(ii) and Cd(ii) 1D coordination polymers: photosalient to non-salient behaviour

“…S8, ESI †). 28,37,38 To get better insight into the photomechanical behavior, the faces of the single crystal of 1 have been indexed. It can be noticed that the (110) plane is cleaved in the crystal under UV light, which indicates that [Zn 2 (CO 2 ) 4 ] dimers that propagate along the a-axis are disrupted.…”

Tunable photosalient behaviours within coordination polymers via functional molecular prearrangements

“…Coordination polymers offer some advantages in this respect, including better thermal stability and the potential for multi-stimuli behaviours related to redox reactions of the metal centres. 1,6,7,[24][25][26] The photosalient (PS) properties 12 arising from a [2+2] cycloaddition reaction are mainly due to the strain energy accumulated during the rapid structural transformation. 9,24,27 This release of energy over a relatively short period of time often results in crystal disintegration.…”

“…Coordination polymers offer some advantages in this respect, including better thermal stability and the potential for multi-stimuli behaviours related to redox reactions of the metal centres. 1,6,7,24–26…”