Suprachannel as a Radical Trap: Crystal Structure of Single Carbon Radicals

Abstract

We report proof-of-concept experiments on the unprecedented crystal structure of an iodomethyl radical (· CH 2 I) nestled within an ensemble's suprachannel via single crystal-to-single crystal photoreaction without destruction of the suprachannel. The trapped nonconjugated carbon radical was additionally confirmed by EPR, 13 C MAS, UPS, and Raman spectra. C rystal engineering on molecular behavior within a confined space has been directed toward practical and timely host-material applications such as gas storage and separation, stabilization of reactive intermediates, drug delivery, biomolecular recognition, catalysis, medical imaging, ion conduction, energy transfer, and membrane structures. 1−7 Recently, such porous materials that do not change their underlying skeleton have been utilized as new task-specific trapping-matrices of liquid molecules and unstable molecules for single-crystal X-ray crystallography. 8,9 Characterization technology based on confined molecules within available channels, for example, is an exciting emerging focus of research, as single-crystal diffraction can clearly reveal three-dimensional structural information on gas or liquid products that cannot be solved by the conventional X-ray crystallographic method.Meanwhile, diiodomethane (CH 2 I 2 ) is an unsafe molecule with respect to both human health and (in its destruction of ozone molecules) the atmosphere's oxidative capability. 10 In contrast, it is also a useful reagent for determination of mineralsample densities and as an optical contact liquid. 11 Thus, clear and comprehensive structural information on the recognition, capture, and decomposition of CH 2 I 2 species is an urgent issue. To date, excitation of CH 2 I 2 in condensed phases via UV, direct photoionization, and radiolysis has been intensively carried out, 12−15 and its photodecomposed species such as trapped electrons, the cation of CH 2 I 2 , radicals, and the isomer of CH 2 I 2 are hot issues. [12][13][14]16 In particular, a close investigation of the nonconjugated carbon radical species ·CH n X 3−n (X = F, Cl, Br, I; n = 0−2) is a fascinating field. 17−19 Even though the structural determination of delocalized diphenyl carbenes was reported, 20−22 crystal-structural analysis of single-carbon-radical species remains an unfulfilled ambition.In this context, two crucial aims of the present research were to explore the photodegradation of the CH 2 I 2 molecules nestled within a unique suprachannel via single crystal-to-single crystal photoreaction 23−25 and to efficiently trap the radical species in the suprachannel crystal for X-ray crystal-structural determination. In this communication, we report proof-ofconcept observations on the single crystal-to-single crystal transformation of CH 2 I 2 @[ZnI 2 L] 2 ·2CH 2 I 2 to (0.3 ·CH 2 I + 0.85 I 2 )@[ZnI 2 L] 2 ·2CH 2 I 2 via UV irradiation along with the Xray crystal structure of the single-carbon-radical species, ·CH 2 I, in the solid state. This suprachannel system safely stores unstable CH 2 I 2 molecules and activates...

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VUV Photofragmentation of Chloroiodomethane: The Iso-CH2I–Cl and Iso-CH2Cl–I Radical Cation Formation

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