Mössbauer, Electron Paramagnetic Resonance, and Theoretical Study of a High-Spin, Four-Coordinate Fe(II) Diketiminate Complex

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• 作者：Sebastian A. Stoian ; Jeremy M. Smith ; Patrick L. Holland ; Eckard Mu&#776 ; nck ; Emile L. Bominaar
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：October 6, 2008
• 年：2008
• 卷：47
• 期：19
• 页码：8687-8695
• 全文大小：344K
• 年卷期：v.47,no.19(October 6, 2008)
• ISSN：1520-510X

文摘

The iron(II) complex LFeCl₂Li(THF)₂ (L = β-diketiminate), 1, has been studied with variable-temperature, variable-field Mössbauer spectroscopy and parallel mode electron paramagnetic resonance (EPR) spectroscopy in both solution and the solid state. In zero applied field the 4.2 K Mössbauer spectrum exhibits an isomer shift δ = 0.90 mm/s and quadrupole splitting ΔE_Q = 2.4 mm/s, values that are typical for the high-spin (S = 2) state anticipated for the iron in 1. Spectra recorded in applied magnetic fields yield an anisotropic magnetic hyperfine tensor with A_x = +2.3 (+1.0) T, A_y = A_z = −21.5 T (solution) and a nearly axial zero-field splitting of the spin quintet with D = D_x 776; −14 cm⁻¹ and rhombicity E/D 776; 0.1. The small, positive value for A_x results from the presence of residual orbital angular momentum along x. The EPR analysis gives g_x 776; 2.4 (and g_y 776; g_z 776; 2.0) and reveals a split “M_S = ± 2” ground doublet with a gap distributed around Δ = 0.42 cm⁻¹. The Mössbauer spectra of 1 show unusual features that arise from the presence of orientation-dependent relaxation and a distribution in the magnetic hyperfine field along x. The origin of the distribution has been analyzed using crystal field theory. The analysis indicates that the distribution in the magnetic hyperfine field originates from a narrow distribution, σ_ϕ 776; 0.5°, in torsion angle ϕ between the FeN₂ and FeCl₂ planes, arising from minute inhomogeneities in the molecular environments.