Unexpected Photoreactivity in a NO₂-Functionalized Aluminum-MOF

Abstract

The metal–organic framework CAU-10-NO2 [Al­(OH)­BDC-NO2] (CAU stands for Christian-Albrechts-University; H2BDC-NO2 is 5-nitroisophthalic acid) was observed to exhibit unexpected photochemical reactivity. Upon irradiation of the MOF with UV light with a wavelength of 365 nm (or with sunlight), guest molecules inside the pore system of the MOF can be oxidized and stable radicals are formed from the organic linker molecules. The reactivity toward different alcohols was studied by UV/vis spectroscopy and EPR spectroscopy. The amount of generated radicals depends on the size of the solvent molecules; however, as an exception, methanol shows a much lower reactivity than ethanol. DFT calculations were carried out to gain insights into these photochemical reactions. The results indicate that the nitro group is reduced to form a nitroso moiety. This was confirmed by means of NMR spectroscopy. The exact nature of the radical could not be revealed, but the results indicate that it could be a further reduced anionic nitroso radical. Methanol and ethanol can be distinguished using this photochemical reaction simply by the coloring of the irradiated MOF. Such a property is characteristic for a sensor; therefore, a synthesis procedure was developed to implement the MOF into a device by which the compound was directly grown onto gold substrates.

Functionalization of Metal–Organic Frameworks for Photoactive Materials

“…Photoirradiation on dried CID‐N 3 in situ converted the stable azide groups into bare triplet nitrenes ( Figure ), and photoirradiation on dried CID‐N 3 in an O 2 atmosphere (80 kPa) resulted in the generation of nitro‐ and nitroso‐functionalized MOFs through nitrene intermediates in the porous solid state. An unexpected photoreaction was recently reported by Stock and co‐workers . Upon photoirradiation of a nitroisophthalic acid‐based MOF containing guest molecules, a stable radical was created, which was attributed to the formation of an anionic nitroso radical from the organic nitro ligand.…”

Relative capability demonstration of luminescent Al-MOFs for ideal detection of nitroaromatic explosives

“…The Al-MOF was synthesised using a well-known method without any modification. 17 Here, 5-nitroisophthalic acid (0.1440 g, 6.82 mmol) and 3.4 mL aluminium chloride hexahydrate (AlCl 3 ·6H 2 O) solution (2 M in H 2 O) were added to 4 mL N , N -dimethylformamide (DMF) and 12.6 mL H 2 O solution in a screw cap bottle. After 12 hours of heating at 120 °C, the mixture was cooled at room temperature and filtered.…”

Photochemistry of framework-supported M(diimine)(CO) 3 X complexes in three-dimensional lithium carboxylate metal–organic frameworks: monitoring the effect of framework cations

“…All other chemicals and solvents were purchased from commercial sources and were used as received without any further purification. 1 H NMR and 13 C NMR spectra were obtained using a Bruker DPX 300 spectrometer or a Bruker DPX400 spectrometer; residual signals of solvent were used for reference. Electrospray ionization mass spectra were collected using a Bruker Daltonics micro-TOF mass spectrometer.…”

“…One area that has emerged over recent years is the incorporation of photoactive components within MOFs [11,12] whose properties can subsequently be exploited. A variety of different photoactive components have been targeted, including systems with photoactive ligands [13,14] but also systems where photoactive moieties such as [Ru(bipy) 3 ] 2+ [15] and, more importantly for this particular study, M(CO) 3 X(diimine) (M = Re, Mn) groups have been investigated [16][17][18][19][20]. Indeed, both Re(CO) 3 X(diimine) [16] and Mn(CO) 3 X(diimine) [17] have been employed for the photocatalytic reduction of CO 2 .…”