Spectroscopic and Computational Studies of a trans-μ-1,2-Disulfido-Bridged Dinickel Species, [{(tmc)Ni}2(S2)](OTf)2: Comparison of End-on Disulfido and Per

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• 作者：Katherine M. Van Heuvelen ; Matthew T. Kieber-Emmons ; Charles G. Riordan ; Thomas C. Brunold
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：April 5, 2010
• 年：2010
• 卷：49
• 期：7
• 页码：3104-3112
• 全文大小：895K
• 年卷期：v.49,no.7(April 5, 2010)
• ISSN：1520-510X

文摘

A powerful means of enhancing our understanding of the structures and functions of enzymes that contain nickel−sulfur bonds, such as Ni superoxide dismutase, acetyl-coenzyme A synthase/carbon monoxide dehydrogenase, [NiFe] hydrogenase, and methyl-CoM reductase, involves the investigation of model compounds with similar structural and/or electronic properties. In this study, we have characterized a trans-μ-1,2-disulfido-bridged dinickel(II) species, [{(tmc)Ni}₂(S₂)]²⁺ (1, tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) by using electronic absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopic techniques, as well as density functional theory (DFT) and time-dependent DFT computational methods. Our computational results, validated on the basis of the experimental MCD data and previously reported ¹H NMR spectra, reveal that 1 is best described as containing two antiferromagnetically coupled high-spin Ni^II centers. A normal coordinate analysis of the rR vibrational data was performed to quantify the core bond strengths, yielding force constants of k_Ni−S = 2.69 mdyn/Å and k_S−S = 2.40 mdyn/Å. These values provide a useful basis for a comparison of metal−S/O bonding in 1 and related Ni₂(O₂), Cu₂(O₂), and Cu₂(S₂) dimers. In both the disulfido and the peroxo species, the lower effective nuclear charge of Ni^II as compared to Cu^II results in a decreased covalency, and thus relatively weaker metal−S/O bonding interactions in the Ni₂ dimers than in the Cu₂ complexes.