title: Mixed-valent dicobalt and iron-cobalt complexes with high-spin configurations and short metal-metal bonds.
abstract: Cobalt-cobalt and iron-cobalt bonds are investigated in coordination complexes with formally mixed-valent [M2](3+) cores. The trigonal dicobalt tris(diphenylformamidinate) compound, Co2(DPhF)3, which was previously reported by Cotton, Murillo, and co-workers (Inorg. Chim. Acta 1996, 249, 9), is shown to have an energetically isolated, high-spin sextet ground-state by magnetic susceptibility and electron paramagnetic resonance (EPR) spectroscopy. A new tris(amidinato)amine ligand platform is introduced. By tethering three amidinate donors to an apical amine, this platform offers two distinct metal-binding sites. Using the phenyl-substituted variant (abbreviated as L(Ph)), the isolation of a dicobalt homobimetallic and an iron-cobalt heterobimetallic are demonstrated. The new [Co2](3+) and [FeCo](3+) cores have high-spin sextet and septet ground states, respectively. Their solid-state structures reveal short metal-metal bond distances of 2.29 Å for Co-Co and 2.18 Å for Fe-Co; the latter is the shortest distance for an iron-cobalt bond to date. To assign the positions of iron and cobalt atoms as well as to determine if Fe/Co mixing is occurring, X-ray anomalous scattering experiments were performed, spanning the Fe and Co absorption energies. These studies show only a minor amount of metal-site mixing in this complex, and that FeCoL(Ph) is more precisely described as (Fe0.94(1)Co0.06(1))(Co0.95(1)Fe0.05(1))L(Ph). The iron-cobalt heterobimetallic has been further characterized by Mössbauer spectroscopy. Its isomer shift of 0.65 mm/s and quadrupole splitting of 0.64 mm/s are comparable to the related diiron complex, Fe2(DPhF)3. On the basis of spectroscopic data and theoretical calculations, it is proposed that the formal [M2](3+) cores are fully delocalized.
authors.affiliation: Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Zall
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Clouston
authors.forename: Victor G
authors.initials: VG
authors.lastname: Young
authors.forename: Keying
authors.initials: K
authors.lastname: Ding
authors.forename: Hyun Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Danylo
authors.initials: D
authors.lastname: Zherebetskyy
authors.forename: Yu-Sheng
authors.initials: YS
authors.lastname: Chen
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Laura
authors.initials: L
authors.lastname: Gagliardi
authors.forename: Connie C
authors.initials: CC
authors.lastname: Lu
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D005559:Formamides / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D005559:Formamides; D009942:Organometallic Compounds; D003035:Cobalt; C017255:diphenylformamide