The Oxidation of Metals with Liebig Acids

Abstract

In Liebig's definition, an acid is a compound which contains one or more hydrogen atoms which may be substituted by metal atoms. Hence, reactions of Liebig acids in substance, excluding water or any other solvent, with non-noble metals yield salts and release hydrogen. In this sense, not only the classical mineral acids such as sulfuric or nitric acid, respectively, are Liebig acids. Rather, there is a large variety of organic compounds with, for example, HO-or HN-functions with acid constants that allow for substitution of the hydrogen atoms by a metal atom. Simple covalent hydrides like water and ammonia or even methane may also 201 act as Liebig acids with conditions properly chosen. The ammonium ion, (NH 4 ) ϩ , represents a special case as it is available in a large variety of salts and may react as an acid/oxidant or as a (base)/reductant and is also a pseudo alkali-metal cation. The versatility of the ammonium ion is reviewed with special emphasis to its ability to function as a Liebig acid, i.e., reactions of, especially, ammonium halides with non-noble metals.

Enhancing the Value of Free Metals in the Synthesis of Lanthanoid Formamidinates: Is a Co‐oxidant Needed?

“…The direct reaction of Ln elements with Liebig (Brønsted) acids is a conceptually simple route to rare‐earth complexes [Scheme , Eq. (1)] …”

Crystal Structures of Ag2ZrF6·8NH3 and Ag2HfF6·8NH3 and Their Synthesis by the “Reactive Fluoride Route” in Liquid Ammonia

“…[6] Several representatives have been characterized structurally by Meyer and co-workers who used NH 4 F, NH 4 HF 2 , or N 2 H 6 F 2 to oxidize the respective metals and half-metals in sealed metal ampoules at higher temperatures to produce for example Zr(NH 3 )F 4 and Hf(NH 3 )F 4 . [8,9] Others used supercritical ammonia at 400°C for the preparation of AlF 3 (NH 3 ) 2 and InF 2 (NH 2 )(NH 3 ) [10] or ammonolysis at higher temperatures with gaseous ammonia (NH 4 [Ge(NH 3 )F 5 ], [11] Sn(NH 2 ) 2 -F 2 [12] ). Our method is based on the use of metal fluorides with the metal in an "unusual" oxidation state -here Ag IIin order to bypass the high lattice energy and allow dissolution in liquid ammonia.…”

Synthesis of Rare Earth (Oxo)nitridocarbonates by Employment of Supercritical Carbon Dioxide, Single‐source Precursor, Solid‐State, and Ion Exchange Reactions

“…Nevertheless only a few reports [38,39] are known about alkaline earth and lanthanide cyanates and to the best of our knowledge neither systematic investigations nor any structural information has been published for homoleptic cyanates of the latter elements. The decomposition of urea at approximately 130 °C, yielding isocyanic acid and ammonia, can be utilized to oxidize electropositive metals such as Eu or Sr. [40,41] The reaction of three equivalents of urea with Sr or Eu metal in closed [Eu(OCN) 2 (urea)]; [7] for the latter unknown phases are also observed in the PXRD of the residue. In contrast to the respective thiocyanates of Eu and Sr, cyanates are more temperature sensitive and decompose without melting.…”