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A detailed mass-spectrometric study provides insight into the gas-phase fragmentation pathways of a cyclic helicate selectively built from four iron(II) centers and six [2.2]cyclophane-based ligands through the subcomponent self-assembly approach. The charge state of the precursor ion, i. e., the number of triflate anions accompanying the metallo-supramolecular core, has a strong influence on the observed fragmentations. The triply charged ion shows loss of a neutral ligand whereas ions of higher charge fragment by up to three different charge-separating pathways to minimize the charge density of the ions. Additional subsequent fragmentations of highly charged fragment ions include redox processes as well as splitting of the unusual paracyclophane backbone., (© 2020 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

The Fe III azide complexes [Fe III (N 3 )cyclam-ac]PF 6 (1⋅PF 6 ), [Fe III (N 3 )Me 3 cyclam-ac]PF 6 (2⋅PF 6 ), and trans-[Fe III (N 3 ) 2 cyclam]ClO 4 (3⋅ClO 4 ) (cyclam=1,4,8,11-tetraazacyclotetradecane; cyclam-ac=1,4,8,11-tetraazacyclotetradecane-1-acetate; Me 3 cyclam-ac=4,8,11-trimethyl-1,4,8,11-tetraazacyclotetra-decane-1-acetate) are studied in the gas phase with special emphasis on the formation of high-valent iron nitrides by collision-induced dissociation. Whereas the azide complex with unsubstituted cyclam-acetate 1 as major fragmentation expels N 2 to form a high-valent Fe V nitride complex, a similar process is not observed for its methyl-substituted congener. In contrast, loss of an azide radical results in iron reduction to Fe II . Thus, the gas-phase behavior is parallel to the results obtained in spectroscopic studies of photolyzed frozen solution. The diazide complex 3 mainly fragments via consecutive losses of HN 3 without change in the iron oxidation state. However, small amounts of dinitrogen loss and thus Fe V nitride formation are also observed. While it is assumed that the Fe V nitride complex detected by Mössbauer spectroscopy in frozen solution is still coordinated by an azide in the trans position to the nitride, both the complex [Fe V (N)(N 3 )(cyclam)] + still bearing an intact second azide and the coordinatively unsaturated [Fe V (N)(cyclam-H)] + are observed in the gas phase., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)