Mössbauer and Computational Study of an N2-Bridged Diiron Diketiminate Complex: Parallel Alignment of the Iron Spins by Direct Antiferromagnetic Exchange with Activated Dinitrogen

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• 作者：Sebastian A. Stoian ; Javier Vela ; Jeremy M. Smith ; Azwana R. Sadique ; Patrick L. Holland ; Eckard M&uuml ; nck ; Emile L. Bominaar
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：August 9, 2006
• 年：2006
• 卷：128
• 期：31
• 页码：10181 - 10192
• 全文大小：331K
• 年卷期：v.128,no.31(August 9, 2006)
• ISSN：1520-5126

文摘

This work reports Mössbauer and DFT studies of the diiron-N₂ complex L^MeFeNNFeL^Me (L =ages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-diketiminate), 1a. Complex 1a, formally diiron(I), has a system spin S = 3 with an isolated M_S = ±3quasi-doublet as a ground state; the M_S = ±2 doublet is >100 cm^-1 higher in energy. Complex 1a exhibitsat 4.2 K a large, positive magnetic hyperfine field, B_int = +68.1 T, and an effective g value of 16 ± 2 alongthe easy magnetization axis of the ground doublet; this value is significantly larger than the spin-only value(g = 12). These results have been rationalized by DFT calculations, which show that each Fe site donatessignificant electron density into the ages/gifchars/pi.gif" BORDER=0 >* orbitals of dinitrogen, resulting in a configuration best described astwo high-spin Fe^II (S_a = S_b = 2) bridged by triplet N₂^2- (S_c = 1). In this description the minority spin electronof each iron is accommodated by two nonbonding, closely spaced 3d orbitals, z² and yz (z is perpendicularto the diketiminate planes, x is along the Fe···Fe vector). Spin-orbit coupling between these orbital statesgenerates a large unquenched orbital momentum along the iron-iron vector. The S = 3 ground state of1a results from strong antiferromagnetic direct exchange couplings of the Fe spins (S_a = S_b = 2) to theN₂^2- spin (S_c = 1) and can be formulated as ages/entities/verbar.gif">((S_a,S_b)S_ab = 4, S_c = 1), S = 3>; H = J(S_a + S_b)·S_c with J ages/entities/ap.gif">3500 cm^-1.