Bis(imino)pyridine Iron Dinitrogen Compounds Revisited: Differences in Electronic Structure Between Four- and Five-Coordinate Derivatives.

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• 作者：S. Chantal E. Stieber ; Carsten Milsmann ; Jordan M. Hoyt ; Zo毛 R. Turner ; Kenneth D. Finkelstein ; Karl Wieghardt ; Serena DeBeer ; Paul J. Chirik
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：March 19, 2012
• 年：2012
• 卷：51
• 期：6
• 页码：3770-3785
• 全文大小：760K
• 年卷期：v.51,no.6(March 19, 2012)
• ISSN：1520-510X

文摘

The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, (^iPrPDI)FeN₂ and (^iPrPDI)Fe(N₂)₂ (^iPrPDI = 2,6-(2,6-ⁱPr₂鈥揅₆H₃鈥揘=CMe)₂C₅H₃N), have been investigated by a combination of spectroscopic techniques (NMR, M枚ssbauer, X-ray Absorption, and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, (^iPrRPDI)FeN₂ (^iPrRPDI = 2,6-(2,6-ⁱPr₂鈥揅₆H₃鈥揘=CR)₂C₅H₃N; R = Et, ⁱPr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the (^iPrRPDI)FeN₂ compounds are intermediate spin ferrous derivatives (S_Fe = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S_PDI = 1). While this ground state description is identical to that previously reported for (^iPrPDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally 蟽-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For (^iPrRPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the (^iPrRPDI)FeN₂ family, one of the iron singly occupied molecular orbitals (SOMOs) is essentially d_z² in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of (^iPrRPDI)FeN₂ and (^iPrPDI)Fe(DMAP) differ from (^iPrPDI)Fe(N₂)₂, a highly covalent molecule with a redox noninnocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.