Topotactic Solid-State Metal Hydride Reductions of Sr sub(2)MnO sub(4)

• Published in: Inorganic chemistry Vol. 54; no. 9; pp. 4249 - 4256
• Main Authors: Hernden, Bradley C, Lussier, Joey A, Bieringer, Mario
• Format: Journal Article
• Language: English
• Published: 04.05.2015
• Subjects: Approximation; Diffraction; Electronegativity; Hydrides; Metal hydrides; Phases; Reduction; X-rays
• ISSN: 0020-1669
• DOI: 10.1021/ic502932x

We report novel details regarding the reactivity and mechanism of the solid-state topotactic reduction of Sr sub(2)MnO sub(4) using a series of solid-state metal hydrides. Comprehensive details describing the active reducing species are reported and comments on the reductive mechanism are provided, where it is shown that more than one electron is being donated by H-. Commonly used solid-state hydrides LiH, NaH, and CaH sub(2) were characterized in terms of reducing power. In addition the unexplored solid-state hydrides MgH sub(2), SrH sub(2), and BaH sub(2) are evaluated as potential solid-state reductants and characterized in terms of their reductive reactivities. These 6 group I and II metal hydrides show the following trend in terms of reactivity: MgH sub(2) < SrH sub(2) < LiH [approximate] CaH sub(2) [approximate] BaH sub(2) < NaH. The order of the reductants are discussed in terms of metal electronegativity and bond strengths. NaH and the novel use of SrH sub(2) allowed for targeted synthesis of reduced Sr sub(2)MnO sub(4-x) (0 [< or =] x [< or =] 0.37) phases. The enhanced control during synthesis demonstrated by this soft chemistry approach has allowed for a more comprehensive and systematic evaluation of Sr sub(2)MnO sub(4-x) phases than previously reported phases prepared by high temperature methods. Sr sub(2)MnO sub(3.63(1)) has for the first time been shown to be monoclinic by powder X-ray diffraction and the oxidative monoclinic to tetragonal transition occurs at 450 [degrees]C.