NO Reactions Inside Crystals

Abstract

AbstractReactions of chemisorbed reagents inside the crystalline molecular solid state are rare but offer unexploited methods for selective solvent‐free chemical synthesis. Here we show that the greenhouse gas precursor, nitric oxide (NO) is chemisorbed by crystals of the hexafluorophosphate salts of complexes containing dicobalt sites. On NO sorption a cascade of reactions results in the in‐crystal synthesis of nitrite and other gaseous NOx. Recrystallization enabled structural elucidation of the mixed valent {[(bpbp)Co2(μ‐(η1‐O : η1‐N)‐ONO)]2(bdc)}4+ (bpbp=2,6‐bis(N,N‐bis(2‐pyridylmethyl)aminomethyl)‐4‐tert‐butylphenolato, bdc=1,4‐benzenedicarboxylato) cation. Overlapping signals in the solid‐state EPR spectra confirm the CoIICoIII oxidation state and the presence of NO2 trapped inside the unrecrystallised solid products (br. g=4, triplet g=2 (340 mT), A(N)=73 MHz), despite three cycles of vacuum and N2 flushing. Consistently, νN−O bands appear in the Raman and IR spectra that are due to the coordinated nitrate and the trapped NO2 that were synthesized in‐crystal. The latter is expelled by heating the solid to 160 °C or by recrystallization. Dimetallic cooperativity is proposed for the NO transformations in these rare examples of selective, chemisorptive substrate reactions in the solid‐state.