Structure, spectroscopy, stability, and bridge exchange in the M₃O₄ incomplete-cubane complexes, [M(III)₃(Sal-AHA)₃(μ-OR)]⁻ (M = Fe, Ga)

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• 作者：Mark A. Chrisman^a ; Robert R. Baum^b ; Jennifer E. Grabo^a ; Jeanette A. Krause^a ; David L. Tierney^b ; Michael J. Baldwin^a ; ^{Michael.baldwin@uc.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：α-Hydroxy acid ; Fe cluster ; Ga cluster ; Cubane ; Bridge exchange
• 刊名：Polyhedron
• 出版年：2015
• 出版时间：4 November 2015
• 年：2015
• 卷：100
• 期：Complete
• 页码：164-169
• 全文大小：681 K

文摘

The [Ga(III)₃(3,5-diCl-Sal-AHA)₃(μ-OCH₃)]⁻ anion crystallizes with one K⁺ and one H₃O⁺ counter ion between each pair of anions. The structure is analogous to the previously reported [Fe(III)₃(3,5-diCl-Sal-AHA)₃(μ-OCH₃)]⁻, with each containing a M₃O₄ incomplete cubane at the base of a phenyl-derived pocket that surrounds a triply bridging methoxy group. The EPR spectrum of [Fe(III)₃(3,5-diCl-Sal-AHA)₃(μ-OCH₃)]⁻ at 4.5 K is complex with features near g_eff = 2, 4.3, and above 5. Only the 4.30 feature maintains intensity much above 30 K, and it persists to above 150 K. Room temperature magnetic susceptibility measurements indicate an average spin of S = 5/2 per trimer in both solid and solution. Both the Ga and Fe clusters are stable in methanol. However, the Ga complex slowly decomposes in 40% water or in the presence of EDTA, while the Fe cluster does not. Experiments with a mixed Fe/Ga solution show that the order of stability of the [M(III)₃(3,5-diCl-Sal-AHA)₃(μ-OCH₃)]⁻, clusters in the presence of EDTA is M(III)₃ = Fe₃ > Fe₂Ga > FeGa₂ > Ga₃. Metal or chelate exchange occurs very slowly (weeks to months) if at all. However, the μ₃-methoxy bridge can be replaced by deuterated methoxy or a μ₃-hydroxy bridge within hours to days.