Communication pubs.acs.org/cm
Anionic Ordering in Ba15V12S34O3, Affording Three Oxidation States of Vanadium and a Quasi-One-Dimensional Magnetic Lattice Christina Jessica Wong,† Emily Jane Hopkins,†,‡ Yurii Prots,† Zhiwei Hu,† Chang-Yang Kuo,† Tun-Wen Pi,§ and Martin Valldor*,† †
Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straβe 40, 01187 Dresden, Germany National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, R.O.C.
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S Supporting Information *
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ompounds containing three or more distinct oxidation states of a single atom type have been suggested but only proven unambiguously by electron energy loss spectroscopy (EELS) in the Mn-based compound La4Mn5Si4O22.1 In Ba3Co10O17, the charge-ordering of CoII/III/IV was claimed, however, only on the basis of bond valence sum calculations.2 In the case of Sr6V9S22O2, vanadium was suggested to have VV and average VIII/IV oxidation states agreeing with the reported semiconducting behavior but disagreeing with the lack of paramagnetic moment.3 The presence of multiple oxidation states of one atomic species is gaining considerable attention due to potentially outstanding properties. For example, the two oxidation states in La0.5Ca0.5MnO3,4,5 are suggested to result in unusual magnetic properties, where a ferromagnetic metallic state coexists with antiferromagnetism and charge-ordering in its ground states. Other charge-ordered compounds with two oxidation states include, e.g., Fe2OBO36 and Ba3V2S4O3.7 The charge ordering phenomenon induces properties such as “colossal” magnetoresistances8 and metal−insulator transitions, where the Verway transition in magnetite is prominent.9 Naturally, the rarity of triple valence compounds is also a consequence of that only few transition metals (TMs) can assume several oxidation states under normal conditions. However, it remains challenging to stabilize three oxidation states simultaneously in a common lattice, and it requires extensive design of the host lattice to prevent phase segregations. The electrochemical potential must be compensated for by constructing a crystal structure with anionic ordering, affording different cationic coordination possibilities. Hence, proofs of three (or more) oxidation states in a single compound have, to our knowledge, been reported only once.1 Spectroscopy delivers the most convincing data, necessary to prove the presence of multiple oxidation states. Therefore, we used X-ray absorption spectroscopy (XAS), to investigate the novel solid-state crystalline compound Ba15V12S34O3 (Figure 1) containing charge-ordered VIII/IV/V. This communication contains syntheses of pure powders and small single crystals of the title compound along with its crystal structure description, synchrotron powder X-ray diffraction, X-ray absorption spectroscopy, and basic physical properties of Ba15V12S34O3. To make pure powders of Ba15V12S34O3, a mixture of BaS, BaO, V, and S was reacted in closed vessels. A detailed description of the synthetic route is present in the Supporting Information (S1 and S2). To confirm the chemical formula of the synthesized powder, inductive coupled plasma-optic © XXXX American Chemical Society
Figure 1. Polyhedral representation of the Ba15V12S34O3 crystal structure, displaying different vanadium environments. Split positions of V1 (a and b) are highlighted, where two colors indicate that one short and one long bond are expected at the O-junction.
emission spectroscopy (ICP-OES) elemental analyses were performed (Table S1, Supporting Information). They are consistent with the nominal composition and the results of the crystal structure determination. From synchrotron radiation data of the title compound, it is possible to conclude that a monoclinic unit cell (a = 6.6937(2), b = 28.8007(7), c = 15.3775(4) Å, α = 90, β = 90.4035(8), γ = 90°) describes almost all observed diffraction intensities. Only a few minor impurity peaks, with
