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Issue 24, 2014
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Influence of the anion nature on styryl dye crystal packing and feasibility of the direct and back [2 + 2] photocycloaddition reactions without single crystal degradation

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Abstract

A family of styryl dyes of the 4-pyridine series, Et–Py+–CH[double bond, length as m-dash]CH–C6H3(OMe)2 X, with different anions X, was synthesized. Their ability to undergo [2 + 2] photocycloaddition (PCA) in the polycrystalline state with the formation of 1,2,3,4-tetrasubstituted rctt cyclobutanes under irradiation with visible light was investigated by 1H NMR spectroscopy. Crystal packing of the dyes and feasibility for the PCA reaction in single crystals were investigated by X-ray structural analysis. Small inorganic anions, such as ClO4, BF4, PF6 that do not form secondary interactions with the organic cation, aid the formation of cation stacking motifs of the “head-to-tail” type. In these stacks, any adjacent cations are arranged in an antiparallel fashion and approach one another at distances shorter than 4.2 Å, which corresponds to the Schmidt's rule for feasibility of PCA reaction in the solid state. As a result of PCA, rctt isomers of cyclobutane derivatives are formed. Success of the PCA reaction without single crystal degradation was only found for the dye containing BF4 anion. Upon irradiation with UV light of the cyclobutane product formed in the crystal, back phototransformation without single crystal degradation was observed. A number of weak interactions I⋯H–C in the dye with I anion prevent significant atomic displacements that accompany the PCA transformation from being achieved. Occurrence of the bulky tosylate anion forming a set of hydrogen bonds with solvate acetonitrile and water molecules aids the formation of “head-to-head” type stacks, with a large separation between the adjacent ethylene bonds. In the dye containing bulky BPh4 anion, the main structure-forming role belongs to anions, which suppress the cation trend to form a stacking packing motif. The dye with picrate anion forms two types of crystals. Crystal packing of one of them excludes any PCA transformation, whereas, the other one permits it, but with single crystal degradation.

Graphical abstract: Influence of the anion nature on styryl dye crystal packing and feasibility of the direct and back [2 + 2] photocycloaddition reactions without single crystal degradation

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Publication details

The article was received on 04 Feb 2014, accepted on 26 Mar 2014 and first published on 27 Mar 2014


Article type: Paper
DOI: 10.1039/C4CE00266K
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Citation: CrystEngComm, 2014,16, 5364-5378
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    Influence of the anion nature on styryl dye crystal packing and feasibility of the direct and back [2 + 2] photocycloaddition reactions without single crystal degradation

    L. G. Kuz'mina, A. I. Vedernikov, A. V. Churakov, E. Kh. Lermontova, J. A. K. Howard, M. V. Alfimov and S. P. Gromov, CrystEngComm, 2014, 16, 5364
    DOI: 10.1039/C4CE00266K

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