title: The modular nature of all-ferrous edge-bridged double cubanes.
abstract: Two all-ferrous, edge-bridged 8Fe-8S clusters, one capped with carbenes (2) and the other with phosphenes (3), have been characterized by (57)Fe Mossbauer spectroscopy. The clusters have diamagnetic ground states that yield spectra consisting of one quadrupole doublet with a large splitting (25% of absorption) and one (3) or two (2) doublets with much smaller splittings (75% of absorption). These patterns closely resemble those observed for all-ferrous 4Fe-4S clusters. Structurally, the 4Fe-4S fragments of 2 and 3 are remarkably similar to all-ferrous 4Fe-4S clusters, sharing with them the characteristic 3:1 pattern of the iron sites, a differentiation that has been shown previously to reflect spontaneous distortions of the cluster core. These spectroscopic and geometric similarities suggest that the diamagnetic ground state of the 8Fe-8S cluster results from antiferromagnetic exchange coupling of two identical 4Fe-4S modules, each carrying spin S(4Fe) = 4. The iron atoms with the largest quadrupole splittings are located at the opposite ends of the body diagonal containing the bridging sulfides.
authors.affiliation: Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Mrinmoy
authors.initials: M
authors.lastname: Chakrabarti
authors.forename: Liang
authors.initials: L
authors.lastname: Deng
authors.forename: R H
authors.initials: RH
authors.lastname: Holm
authors.forename: Eckard
authors.initials: E
authors.lastname: Münck
authors.forename: Emile L
authors.initials: EL
authors.lastname: Bominaar
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism / Q000379:methods; D004220:Disulfides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005296:Ferrous Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008280:Magnetics; D008956:Models, Chemical; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D015204:Spectroscopy, Mossbauer / Q000379:methods*; D013057:Spectrum Analysis; D013059:Spectrum Analysis, Raman; D013440:Sulfides / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D004220:Disulfides; D005296:Ferrous Compounds; D007506:Iron-Sulfur Proteins; D013440:Sulfides; D007501:Iron