Angewandte Communications Chemie International Edition:DOI:10.1002/anie.201605123 Solid-State Structures German Edition:DOI:10.1002/ange.201605123 High-Pressure Synthesis of ManganeseOxyhydride with Partial Anion Order Cedric Tassel, Yoshinori Goto,Daichi Watabe,YaTang,Honcheng Lu, Yoshinori Kuno, Fumitaka Takeiri, Takafumi Yamamoto,Craig M. Brown, James Hester,Yoji Kobayashi, and Hiroshi Kageyama* Abstract: The high-pressure synthesis of amanganese oxy- display H/O ordering,which is however absent in the hydride LaSrMnO3.3H0.7 is reported. Neutron and X-ray chromium and titanium cases.The origin of anion (H/O) Rietveld analyses showed that this compound adopts the order–disorder has been discussed but not yet fully under- K2NiF4 structure with hydride ions positioned exclusively at the stood. equatorial site.This result makes astriking contrast to top- TheTMoxyhydrides exhibit remarkable properties.First, ochemical reductions of LaSrMnO4 that result in only oxygen- LaSrCoO3H0.7,SrCrO2H, and SrVO2Hexhibit magnetic order [4,7, 9] deficient phases down to LaSrMnO3.5.This suggests that high far above room temperature (RT), which is rationalized H2 pressure playsakey role in stabilizing the oxyhydride in LaSrCoO3H0.7 by strong hybridizations between Co 3d eg phase,offering an opportunity to synthesize other transition- and H1sorbitals,and in SrCrO2Hbyrelieved octahedral 3+ metal oxyhydrides.Magnetic susceptibility revealed aspin- tilting (vesrus isoelectronic ACr O3). Thehigh TN in SrVO2H glass transition at 24 Kthat is due to competing ferromagnetic is surprising,given the orthogonality of V3d t2g and H1s (Mn2+–Mn3+)and antiferromagnetic (Mn2+–Mn2,Mn3+– orbitals,and calls for further investigations.Second, titanium Mn3+)interactions. oxyhydrides show ametallic conductivity with carrier density [10] widely tuned by HÀ content. Thelast but not least is high [11] Over the past decades,transition-metal (TM) perovskite- mobility of hydride ions in LaSrCoO3H0.7 and an H/D [6a] based mixed-anion systems,such as oxynitrides and oxy- exchangeability of BaTiO2.4H0.6 with D2 gas, both occurring halides,have been intensively investigated with various at moderate temperatures. novel phenomena, including anon-toxic pigment So far, only four TMs (Cr,Co, Ti,V)are known to afford La1 xSrxTaO 2 xN1+x,ahigh Tc superconductor oxyhydrides,afact which significantly limits our understand- À À [1–3] Ca2 xNaxCuO2Cl2,and avisible-light catalyst Sm2Ti2O5S2. ing and rationalization of their stability,structures,and À TM oxyhydrides are arelatively new class of mixed-anion functions.Herein, we present the HP synthesis of amanganese systems.LaSrCoO3H0.7 was the first example,reported in analogue LaSrMnO4 xHx (x 0.7) with an n = 1RPperov- [4] [5] À 2002, which was followed by Sr3Co2O4.33H0.84. These skite (K2NiF4)structure (Figure 1a). Its structure,stability, compounds were prepared by atopochemical reaction of and physical properties are discussed and compared with [12] n = 1and 2Ruddlesden–Popper (RP) perovskite oxides using CaH2-reduced LaAMnO4 d phases (A = Sr, Ba). We also À CaH2.Subsequently,ATiO3 xHx (A = Ba, Sr, Ca) and argue H/O order–disorder in comparison with other mixed- À Srn+1VnO2n+1Hn (n = 1, 2, )were obtained from ATiO3 and anion compounds. [6] 1 Srn+1VnO3n. More recently,ahigh-pressure (HP) reaction Forthe synthesis of LaSrMnO4 xHx,wevaried temper- À has been shown as an alternate approach to access TM ature (900–11008C), pressure (< 5GPa), and molar ratio of oxyhydrides.SrCrO2Hand Sr2VO4 xHx were stabilized by À reacting amixture of binary oxides and hydrides under 5GPa.[7,8] Interestingly,the cobalt and vanadium oxyhydrides [*] Dr.C.Tassel, Y. Goto, D. Watabe, Dr.H.Lu, Y. Kuno, F. Takeiri, Dr.T.Yamamoto, Dr.Y.Kobayashi, Prof. H. Kageyama Graduate School of Engineering, Kyoto University 615-8510,Kyoto (Japan) E-mail:[email protected] Dr.C.M.Brown Center for Neutron Research National Institute of Standards and Technology (NIST) Gaithersburg, MD 20899 (USA) Dr.J.Hester Bragg Institute Australian Nuclear Science and TechnologyOrganization (ANSTO) Locked Bag 2001, Kirrawee,DCNSW 2232 (Australia) Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: Figure 1. a) LaSrMnO3.3H0.7 structure;b),c) coordination geometry http://dx.doi.org/10.1002/anie.201605123. around Mn (b) and La/Sr (c). Angew.Chem. Int.Ed. 2016, 55,9667 –9670 2016 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim 9667 Angewandte Communications Chemie 2.34+ 2+ 3+ [13] starting reagents.Inappropriate conditions,wefound abody- LaSrMn O3.67,LaSrMn O3.5,and LaSrMn O4, imply- centered tetragonal phase (a 3.82 , c 13.19 ) along ing that the Jahn–Teller (JT) effect of Mn3+ is not amain with impurities.The impurity amount was minimized origin of octahedral distortion. We also observed anisotropic when reacted at 10008Cand 5GPa with peak broadening that may emerge from strains along a and b La2O3 :SrO:SrH2 :MnO:Mn2O3 = 1:1:0.9:1.1:1.4:0.3. As (see structural analysis in Supporting Information), possibly shown in Figure 2, the synchrotron X-ray diffraction arising from randomly distributed short Mn Hand long Mn À À Obonds. It is noteworthy that low-temperature CaH2 reactions of LaSrMnO4 at 4208Cand 4808Cyield only oxygen-deficient [12] phases,LaSrMnO3.67 and LaSrMnO3.5,respectively. The manganese valence of + 2.3 in LaSrMnO3.3H0.7 is close to 2+ LaSrMnO3.67,but is higher than LaSrMn O3.5,implying superiority of CaH2 reduction in terms of yielding compounds with asmaller valence.Even more remarkable is the fact that only HP condition gives an oxyhydride,instead of oxide.We consider HP reaction can avoid decomposition SrH2 to Sr and H2,while allowing incorporation of HÀ in the structure. Possibly,the excess use of SrH2 in the optimized reaction (10%) generates ahigh H2 gas pressure and helps in forming the oxyhydride. Anumber of topochemical reactions using metal hydrides [14] (CaH2,NaH, LiH) have been reported. In most cases,they lead to highly reduced oxides,rather than oxyhydrides.The present result indicates that reduced oxides accessible by topochemical hydride reactions are good candidates for adirect HP reaction to yield oxyhydrides.Itisinteresting to [15,16] revisit, for example,La1 xCaxMnO2+d and 4H-BaMnO2+d, À with the HP method. Atopochemical reaction of oxides with CaH2 under high (H2)pressure will be an alternative strategy. Interestingly,anion vacancies in LaSrMnO3.67 and Figure 2. Rietveld refinement of a) SXRD and b) ND for LaSrM- LaSrMnO3.5 are present only within the MnO2 layers, nO3.3H0.7.The red crosses and green and blue curves indicate the suggesting that if an oxyhydride is allowed to form, the HÀ observed,calculated,and differencedata. Green ticks are the calcu- site is predictable from its oxygen-deficient phase. lated positionofBragg peaks. Asterisks indicate reflections from Themagnetic susceptibility of LaSrMnO3.3H0.7 (Figure 3) unknown impurity. is fitted with the Curie–Weiss formula, c = C/(T q) + c , À 0 where C, q,and c0 denote the Curie constant, the Weiss (SXRD) and neutron diffraction (ND) patterns at RT was temperature and aconstant term, giving C = 3.88- 1 readily indexed with the K2NiF4 structure (I4/mmm)with cell (6) emuKmolÀ , q = 149(3) Kand c0 = 5.8(8) [13] 4 1 À parameters close to LaSrMnO4. TheK2NiF4 structure was 10À emumolÀ .The effective moment of meff = 5.57 mB thus employed for Rietveld refinements with La/Sr at 4e,Mn agrees well with the theoretical value (5.63 mB). The q value at 2a,O1at4c,and O2 at 4e.Wecould not detect sizable indicates strong antiferromagnetic interactions.Adeviation amount of vacancy or hydrogen at the apical O2 site from from the Curie–Weiss law below 80 Ksignifies development ND/SXRD,while SXRD analysis on the equatorial O1 site of short-range spin correlations.Despite the large q ,the j j occupancyshowed the vacancies giving LaSrMnO3.552(32). susceptibility keeps increasing with temperature,until it However,NDanalysis based on the anion vacancy model gave an incoherent composition LaSrMnO2.90(3) with an extremely low Mn valence of + 0.80. As the quadrupole mass spectrometry (Supporting Information, Figure S1) showed arelease of large amount of hydrogen above 1508C, Hwas added at O1 where H/O atoms are randomly distributed at O1. This led to aconsistent stoichiometry of LaSrMnO3.3H0.7.The sample prepared in adifferent condition (having larger amount of impurities) also gave the identical composition (Supporting Information, Figure S2 and Table S2). As shown in Figure 1b,the Mn(H,O)4O2 octahedron is stretched with shorter equatorial Mn O1/H1 bonds (1.9 ) À and longer apical Mn O2 bonds (2.3 ) along the c axis.The À Figure 3. Magnetic susceptibility of LaSrMnO3.3H0.7.Inset:inverse Mn O2/Mn O1 ratio of 1.2 is similar to those of susceptibility and the Curie–Weiss fit (black line). À À 9668 www.angewandte.org 2016 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Angew.Chem. Int. Ed. 2016, 55,9667 –9670 Angewandte Communications Chemie exhibits akink at 22 K(in ZFC process). However,NDdata bO1 = 4zA/vA + 2zB/vB and bO2 = 5zA/vA + zB/vB (z = formal at 6K (Supporting Information, Figure S3) lacks magnetic valence, v = coordination number). Sr2TaO 3Nand Sr2CoO3F reflections,suggesting aspin glass state below TSG = 22 K. A have (bO1, bO2) = (2.56, 1.94) and (1.89, 1.61), implying the [27] deviation between ZFC and FC processes at TSG is consistent occupation of N/F at the O1/O2 site. Interestingly,this rule with the spin glass nature.The AC susceptibility (Supporting does not hold in oxyhydrides:Sr2VO3H(1.89, 1.61), LaSr- Information, Figure S4) displays afrequency (w)variation of CoO3H0.7 (1.68, 1.67), and LaSrMnO3.3H0.7 (1.88, 1.77). The transition temperature (Tf), with w fitted by w = w0 (Tf/ electronegativity of Hmay be too small to apply the principle zu [17] / TSG 1) .