Solid-Phase Quasi-Intramolecular Redox Reaction of [Ag(NH3)2]MnO4: An Easy Way to Prepare Pure AgMnO2.

Lara A Fogaca,Imre M Szilágyi,Éva Kováts,Katalin Kamarás,Vladimir Petruševski,Péter Németh,Gergely Németh,Laura Bereczki,Kende A Béres,István E Sajó,Szilvia Klébert,Berta Barta Holló,Attila Farkas,László Kótai

doi:10.1021/acs.inorgchem.0c03498

Abstract

Two monoclinic polymorphs of [Ag(NH3)2]MnO4 containing a unique coordination mode of permanganate ions were prepared, and the high-temperature polymorph was used as a precursor to synthesize pure AgMnO2. The hydrogen bonds between the permanganate ions and the hydrogen atoms of ammonia were detected by IR spectroscopy and single-crystal X-ray diffraction. Under thermal decomposition, these hydrogen bonds induced a solid-phase quasi-intramolecular redox reaction between the [Ag(NH3)2]+ cation and MnO4– anion even before losing the ammonia ligand or permanganate oxygen atom. The polymorphs decomposed into finely dispersed elementary silver, amorphous MnOx compounds, and H2O, N2 and NO gases. Annealing the primary decomposition product at 573 K, the metallic silver reacted with the manganese oxides and resulted in the formation of amorphous silver manganese oxides, which started to crystallize only at 773 K and completely transformed into AgMnO2 at 873 K.

Highlights

IntroductionUsing pyridine as a ligand/reducing agent results in complexes that during heating decompose into Ag/ Mn3O4 composites without the formation of AgMnOx compounds.[4,10] there is no information about the reductive thermal decomposition of silver permanganate ammonia (NH3) complexes, other transition-metal permanganate complexes could be transformed into spinel-like mixed oxides (MMn2O4, where M = Cu, Zn, and Cd).[11−14] Our previous successful work on the synthesis and studies on the decomposition of compounds having redox-active cationic/anionic parts[3,4,10] prompted us to study ammonia complexes of silver permanganate as potential precursors in the low-temperature (
Solid-phase quasi-intramolecular redox reactions of compounds containing redox-active cations and anions ensure an easy way to prepare nanosized transition-metal oxides, which can be used as catalysts and sensors.[1−5] Reduction of AgMnO4 to {AgMnOx} (x = 2−3; formulas given in { } mean materials with known chemical but unknown phase compositions) type materials plays a key role in the preparation of highly efficient catalysts in CO oxidation[6] and in the combustion of Nheterocycles and chlorinated compounds (Körbl catalysts).[7]
There is no information about the reductive thermal decomposition of silver permanganate ammonia (NH3) complexes, other transition-metal permanganate complexes could be transformed into spinel-like mixed oxides (MMn2O4, where M = Cu, Zn, and Cd).[11−14] Our previous successful work on the synthesis and studies on the decomposition of compounds having redox-active cationic/anionic parts[3,4,10] prompted us to study ammonia complexes of silver permanganate as potential precursors in the low-temperature (

Summary

Introduction

Using pyridine as a ligand/reducing agent results in complexes that during heating decompose into Ag/ Mn3O4 composites without the formation of AgMnOx compounds.[4,10] there is no information about the reductive thermal decomposition of silver permanganate ammonia (NH3) complexes, other transition-metal permanganate complexes could be transformed into spinel-like mixed oxides (MMn2O4, where M = Cu, Zn, and Cd).[11−14] Our previous successful work on the synthesis and studies on the decomposition of compounds having redox-active cationic/anionic parts[3,4,10] prompted us to study ammonia complexes of silver permanganate as potential precursors in the low-temperature (

Objectives

Results

Conclusion