A New Partially Deprotonated Mixed-Valence Manganese(II,III) Hydroxide鈥揂rsenate with Electronic Conductivity: Magnetic Properties of High- and Room-Temperature Sarkinite

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• 作者：Imanol de Pedro ; Jose M. Rojo ; Jordi Rius ; Oriol Vallcorba ; Idoia Ruiz de Larramendi ; Jes煤s Rodr铆guez Fern谩ndez ; Luis Lezama ; Teofilo Rojo
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：May 7, 2012
• 年：2012
• 卷：51
• 期：9
• 页码：5246-5256
• 全文大小：697K
• 年卷期：v.51,no.9(May 7, 2012)
• ISSN：1520-510X

文摘

A new three-dimensional hydroxide鈥揳rsenate compound called compound 2 has been synthesized by heating (in air) of the sarkinite phase, Mn₂(OH)AsO₄ (compound 1), with temperature and time control. The crystal structure of this high-temperature compound has been solved by Patterson-function direct methods. A relevant feature of this new material is that it is actually the first member of the adamite-type family with mixed-valence manganese(II,III) and electronic conductivity. Crystal data: a = 6.7367(5) 脜, b = 7.5220(6) 脜, c = 9.8117(6) 脜, 伪 = 92.410(4)掳, 尾 = 109.840(4)掳, 纬 = 115.946(4)掳, P1̅. The unit cell content derived from Rietveld refinement is Mn₈(O₄H_x)(AsO₄)₄. Its framework, projected along [111], is characterized by rings of eight Mn atoms with the OH^{鈥?/sup>/O2鈥?/sup> inside the rings. These rings form an almost perfect hexagonal arrangement with the AsO₄ groups placed in between. Bond-valence analysis indicates both partial deprotonation (x 3) and the presence of Mn in two different oxidation states (II and III), which is consistent with the electronic conductivity above 300 掳C from electrochemical measurements. The electron paramagnetic resonance spectra of compound 1 and of its high-temperature form compound 2 show the presence of antiferromagnetic interactions with stronger magnetic coupling for the high-temperature phase. Magnetization measurements of room-temperature compound 1 show a complex magnetic behavior, with a three-dimensional antiferromagnetic ordering and magnetic anomalies at low temperatures, whereas for compound 2, an ordered state is not reached. Magnetostructural correlations indicate that superexchange interactions via oxygen are present in both compounds. The values of the magnetic exchange pathways [Mn鈥揙鈥揗n] are characteristic of antiferromagnetic couplings. Notwithstanding, the existence of competition between different magnetic interactions through superexchange pathways can cause the complex magnetic behavior of compound 1. The loss of three-dimensional magnetic ordering by heating of compound 1 could well be based on the presence of Mn3+ ions (d4) in compound 2.}