Mixed-Valent Dicobalt and Iron-Cobalt Complexes with High-Spin Configurations and Short Metal-Metal Bonds

Journal Article · Mon Sep 23 00:00:00 EDT 2013 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic400292g· OSTI ID:1092598

Zall, Christopher M.; Clouston, Laura J.; Ding, Keying; Kim, Hyun Jung; Zherebetskyy, Danylo; Chen, Yu-Sheng; Bill, Eckhard; Gagliardi, Laura; Lu, Connie C. ^[1]

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1. UMM

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 (Fe_0.94(1)Co_0.06(1))(Co_0.95(1)Fe_0.05(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.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: NSFUNIVERSITY
• OSTI ID: 1092598
• Journal Information: Inorganic Chemistry, Vol. 52, Issue (16) ; 08, 2013; ISSN 0020-1669
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: ENGLISH