Trianionic spin-quartet and tetraanionic spin-quintet molecular clusters derived from m-dibenzoylbenzene in solution were identified by CW-ESR/pulse-ESR based two-dimensional electron spin transient nutation spectroscopy, and their spin and clustering structures in the ground state were determined in terms of a D-tensor based phenomenological approach and DFT calculations. The molecular structures obtained semiempirically are supported by DFT-based quantum chemical calculations. The DFT calculations have been tested for a sodium ion bridged fluorenone-based cluster, [fluorenone(-)˙ {Na(+)(dme)(2)}](2), whose crystal structure was reported in the literature [H. Bock, H.-F. Herrmann, D. Fenske and H. Goesmann, Angew. Chem., Int. Ed. Engl., 1988, 27, 1067], reproducing the experimentally determined moelcular structure of the dimer cluster. It is suggested that both the quartet and quintet clusters in the 2-MTHF glass and solution form the cross-typed structures with the two m-dibenzoylbenzene moieties in cis-configuration. A dianionic spin-triplet m-dibenzoylbenzene derivative was detected for the first time and its charge and spin densities were studied by the quantum chemical calculations. The high-spin states of the open-shell entities under study were confirmed by X-band pulse-ESR based electron spin nutation spectroscopy in organic frozen glasses. The D values and other spin Hamiltonian parameters of all the polyanionic high-spin species were determined by the hybrid eigenfield spectral simulation for fine-structure ESR spectra. m-Dibenzoylbenzene provides pseudo-degenerate π-LUMOs arising from its topological symmetry of the π-electron network and its dianion in the triplet ground state is a prototypical model for topologically-controlled genuinely organic ferromagnetic metals.
Seven different aryl methyl ethers (1-7) were reduced by Li, Na, K, and Cs in THF, DME, or mixtures of THF and DME. The resulting solutions were studied by ESR and, in some cases (5-7), by ENDOR and TRIPLE. With the exception of 3 and 4, the resulting ROAr*~M+ radicals could be observed. The experimental electron-spin distributions (including those published for other ethers) were compared with the results of the Hückel-McLachlan and INDO calculations. These combined results and the temperature variation for 6"M+ allowed us to establish the conformations of ROAr*" and the localization of M+. The persistence of ROAr" toward OAr bond scission increases with the corresponding ir-bond order and the oxygen metal distance. The orthogonal conformation favors RO-bond scission, the planar one OAr-bond scission. A new way to understand the influence of structure, conformation, counterion, and solvent on the reactivity and regioselectivity in unimolecular ROAr"M+ fragmentation is presented in terms of a single-step mechanism and by considering the lowering effect of the coulombic field of M+ on the energies of the various species and states involved.Recent publications on alkyl aryl ether cleavage by alkali metals1,2 and by electrolytical reduction,3•4 as well as unpublished material and earlier literature, were reviewed by Maercker,5 who also presents some new mechanistic views on this reaction. The first step leads to radical anions ROAr", known since 1968 from ESR studies.6 Dianions were also been discussed in the past as intermediates,7 *9"12 although the more recent literat 11ure1•5•13"19 shows that in most cases this is an unnecessary hypothesis. Intermediates
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.