Sodium rare earth metal amides Na₃ RE(NH₂)₆ (RE = La–Nd, Er, Yb) from ammonothermal synthesis

Abstract

The amides Na3 RE(NH2)6 have been obtained from the metals in supercritical ammonia under ammonobasic conditions at 573 K and 70 MPa for RE = La–Nd, and at 473 K and 40 MPa for RE = Er, Yb. All compounds are formed in the hot zone within a temperature gradient, indicating a retrograde solubility under the applied process conditions. These amides represent soluble intermediates in ammonothermal binary rare earth metal nitride synthesis. All compounds were obtained as microcrystalline powders, while single crystals of those amides containing the heavier rare earth metals could be isolated. The crystal structures were solved and refined from single-crystal and powder X-ray diffraction intensity data. The results of vibrational spectroscopy are reported. Thermal analysis measurements under inert gas atmosphere demonstrated a decomposition to the respective black binary rare earth metal nitrides REN1−δ .

Ammonothermal Synthesis and Crystal Structure of the Ternary Amide Na2Ba(NH2)4

“…This disorder is probably caused by the smaller ionic radius of sodium (1.02 Å) compared to barium (1.35 Å) which both occupy octahedral voids of nearly the same volume (28.1 Å 3 for Na and 28.3 Å 3 for Ba) [8] . The Na−N distances vary between 2.46(2) and 2.88(3) Å, which is in agreement to the reported distances in the literature for comparable amides (Table S3) [16–17,21–22] . The Ba−N distances in the Ba(NH 2 ) 6 octahedra (Figure 3b) range from 2.7328(12) to 2.8113(10) Å.…”

“…[8] The NaÀ N distances vary between 2.46(2) and 2.88(3) Å, which is in agreement to the reported distances in the literature for comparable amides (Table S3). [16][17][21][22] The BaÀ N distances in the Ba(NH 2 ) 6 octahedra (Figure 3b) range from 2.7328(12) to 2.8113(10) Å. These values correspond to the reported values for barium ions in octahedral coordination in barium-containing amides.…”