Magnetic Behavior of Heterometallic Wheels Having a [MnIV6M2O9]10+ Core with M = Ca2+ and Sr2+

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• 作者：Luis Escriche-Tur ; Jes煤s Jover ; Merc猫 Font-Bardia ; Gabriel Aull贸n ; Montserrat Corbella
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：December 21, 2015
• 年：2015
• 卷：54
• 期：24
• 页码：11596-11605
• 全文大小：546K
• ISSN：1520-510X

文摘

Two new heterometallic Mn^IV鈥揗²⁺ compounds with formula [Mn₆M₂O₉(4-^tBuC₆H₄COO)₁₀(4-^tBuC₆H₄COOH)₅] (M = Ca²⁺ (1), Sr²⁺ (2)) have been crystallized. The core of both compounds consists of a planar Mn₆ ring, where the Mn^IV ions are alternatively bridged by (渭₃-O)₂(渭-RCOO) and (渭₄-O)(渭-RCOO)₂ ligands, and the two alkaline earth ions are located to both sides of the wheel, linked to the oxo bridges, generating three fused [Mn₂M₂O₄]⁴⁺ cuboids. These compounds show a net antiferromagnetic behavior, more important for 2 (Sr²⁺) than for 1 (Ca²⁺). The fitting of the experimental data was performed with the support of DFT calculations, considering four different exchange pathways: two between adjacent Mn^IV ions (J₁ and J₂) and two between nonadjacent Mn^IV ions (J₃ and J₄). The results of the analysis show that J₁ and J₂ are of the opposite sign, the ferromagnetic contribution corresponding to the [Mn₂(渭₄-O)(渭-RCOO)₂]⁴⁺ unit (J₂). The influence of the M²⁺ ions in the magnetic behavior is analyzed for 1 and 2 and for three hypothetical models with the structural parameters of 1 containing Mg²⁺, Sr²⁺ or without the M²⁺ ions. In spite of the diamagnetic character of the alkaline earth ions, their influence on the magnetic behavior has been evidenced and correlated with their polarizing effect. Moreover, the magnetic interactions between nonadjacent ions are non-negligible.