Synthesis of Rare Earth (Oxo)nitridocarbonates by Employment of Supercritical Carbon Dioxide, Single-source Precursor, Solid-State and Ion Exchange Reactions.
Résumé
Novel synthetic approaches to rare earth nitrido- and oxonitridocarbonates are described. Dioxy mono-carbodiimides (Ln2O2CN2) from the second half of the lanthanide series are accessible by insertion of supercritical CO2 into lanthanide amido compounds (e.g. [(Cp2ErNH2)2]), forming single-source precursors. Ammonolysis of amorphous carbamate compounds affords phase pure Ln2O2CN2, which are also accessible via the crystalline carbamate compound [Ln2{µ-η1:η2-OC(OtBu)NH}Cp4] (Ln = Y, Ho, Er, Yb). Urea complexes and homoleptic cyanates of europium and strontium have been synthesized by solid-state reaction of urea with the respective metals. Subsequent thermal treatment (160 240 °C) results in formation of solvent-free homoleptic cyanates. The Eu2+-doped compounds [Sr(OCN)2(urea)]:Eu2+ and Sr(OCN)2:Eu2+ as well as the respective pure Eu-compounds exhibit strong broad band emissions due to 4f65d1-4f7 transitions in the bluish green region. Furthermore, rare earth dicyanamides Ln[N(CN)2]3∙2H2O as well as Ln[N(CN)2]3 with Ln = Eu, Tb, Gd have been prepared by ion exchange in aqueous solution, followed by evaporation of the solvent at room temperature. Condensed nitridocarbonates such as rare earth tricyanomelaminates [NH4]Ln[HC6N9]2[H2O]7∙H2O with Ln = La-Nd, Sm-Dy have been obtained through ion exchange reactions. The luminescence properties of the europium and terbium dicyanamides as well as the tricyanomelaminates have been explored in detail.
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