Three peroxomorphic H2O2 adducts of antibiotic furacin: the first cases of 2D hydrogen-bonded peroxide layers and concerted flip-flop hydrogen disorder of peroxide species†

Crystallization of the antimicrobial compound furacin (nitrofurazone) from 96%, 50%, and 20% hydrogen peroxide (HP) led to three novel solvates C₆H₆N₄O₄·H₂O₂, C₆H₆N₄O₄·1.5(H₂O₂), and C₆H₆N₄O₄·3.5(H₂O₂), respectively. Surprisingly, solvatomorphs that were richer in hydrogen peroxide were obtained from more dilute H₂O₂ solutions. The stability of the compounds decreased with an increase in peroxide content. These compounds represent a rare example of solvatomorphism (peroxomorphism) among crystalline hydrogen peroxide adducts. The structures of all the adducts were determined using X-ray crystallography. All of them contain a 1 : 1 chelating supramolecular synthon with a strong and unusual bifurcated donor hydrogen bond HOOH⋯(O₂N, furane). Compound C₆H₆N₄O₄·3.5(H₂O₂) is the first example of a structure containing 2D hydrogen-bonded layers built exclusively from peroxide molecules. In its crystal, a concerted flip-flop proton disorder of HP molecules was observed for the first time.