A series of iron and iron-cobalt bimetallic complexes were isolated: LFe2Cl (1), LFe2 (2), Li(THF)3[LFe2Cl](Li(THF)3[2-Cl]), LFeCoCl (3), and LFeCo (4), where L is a trianionic tris(phosphineamido)amine ligand. As elucidated by single-crystal X-ray diffraction studies and quantum-chemical calculations, the FeIIFeII and FeIICoII complexes, 1 and 3, respectively, have weak metal-metal interactions (the metal-metal distances are 2.63 and 2.59 Å, respectively) with a partial bond order of 0.5. The formally mixed-valent complexes, FeIIFeI (3) and FeIICoI (4), have short metal-metal bonds (2.32 and 2.26 Å, respectively) with a formal bond order of 1.5. On the basis of magnetic susceptibility measurements, complexes 1-4 are all paramagnetic with high-spin ground states, S = 3-4, which are proposed to arise from ferromagnetic coupling of the two metals' spins through a direct exchange mechanism. Zero- and applied-field Mössbauer spectra corroborate the presence of distinct oxidation and spin states for the iron sites. The reduction potentials of 1 and 3 are -1.48 and -1.60 V (vs Fc+/Fc), respectively. Other characterization data are also reported for this series of complexes, electronic absorption spectra and anomalous X-ray scattering data.
Bibliographical noteFunding Information:
The experimental work (C.C.L.) was supported by the National Science Foundation (Grant CHE-1254621). The theoretical work was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES), under SciDAC Grant DESC0008666 (to L.G.). R.B.S. thanks the NSF for a graduate fellowship. L.J.C. thanks the Graduate School for a dissertation fellowship. X-ray diffraction experiments were performed using a crystal diffractometer acquired through an NSF-MRI award(Grant CHE-1229400) in the X-ray laboratory supervised by Dr. Victor G. Young, Jr. ChemMatCARS Sector 15 is supported by the National Science Foundation under Grant CHE- 1346572.
© 2016 American Chemical Society.