Synthesis of Nanocrystalline Gd₂O₂NCN from a Versatile Single-source Precursor

Nanocrystalline Gd₂O₂NCN (P3m1, crystallite size 30–40 nm) was synthesized upon ammonolysis of bis[[(N-carboxymethyl,N-carboxy-κO-methyl)amino-κN]-ethyl]-glycinato(3-)-κN,κO]gadolinium(III) (diethylenetriamine pentaacetic acid gadolinium(III) dihydrogen salt or gadopentetic acid, Gd-H₂DTPA hereafter) at 900 °C. The conversion of Gd-H₂DTPA into Gd₂O₂NCN takes place in several steps, probably via transient formation of iminodiacetate-, glycinate-, and carbamate-containing complexes of Gd. Thermal treatment in air of Gd-H₂DTPA at 750 and 1300 °C delivers nanocrystalline bixbyite-type Gd₂O₃ (Ia3, crystallite size 30–70 nm); in an argon or nitrogen atmosphere the formation of monoclinic Gd₂O₃ (C2/m) was observed at 1300 °C. The synthesized Gd₂O₂NCN converts upon thermal treatment in air, nitrogen, or argon atmosphere into monoclinic Gd₂O₃ (C2/m). In ammonia atmosphere, Gd₂O₂NCN seems to be stable against decomposition, even upon prolonged exposure to 1000 °C. This study indicates that Gd-H₂DTPA may be a robust, low-cost, and flexible precursor for nanoscaled Gd-based nanopowders. Moreover, precursor approaches based on metal complexes using H₅DTPA as a ligand are suggested as promising access pathways towards nanocrystalline materials in the M/O/C/N system.