Conversion of [(^tBuCH₂)₂TaN]₅ to Cubic TaN:  Related Syntheses, EHMO Calculations, and MAS and Spin Echo ¹⁵N NMR Spectroscopies

Abstract

The conversion of pentamer [( t BuCH2)2TaN]5 (2) and ammonia to cubic TaN0.8 (5) proceeds via precipitate 1/n[TaC1.41H3.90N1.90] n (3) and amorphous TaN (4). Precursors other than ( t BuCH2)3TaCH t Bu (1) and NH3, which provided 2, such as Ta(NMe2)5 (7) and NH3, (Me2N)3TaN t Bu (9) and NH3, also afforded 5. Extended Hückel molecular orbital calculations were conducted to examine the electronic changes that appear upon oligomerization of hypothetical Me2TaN to (Me2TaN)∞, as a model for pentamer 2 formation. The relationship between pentamer 2 and the remaining nitrides, 3−5 was probed via magic angle spinning (MAS) and spin-echo solid-state 15N NMR experiments that probe the local environments of the various nitrogen atoms. In combination with 15N-labeling studies, the spin-echo spectra were used in an effort to analyze the possibility of a direct relationship between the 2-dimensional Ta2N2 “squares” of the pentamer (2) and the 3-dimensional Ta4N4 “cubes” of the ultimate product, cubic TaN0.8 (5).

Heterometallic Cube‐Type Molecular Nitrides

“…[24] For instance, Wolczanski and co-workers demonstrated that the geometry of the nitrido tantalum precursor [{Ta(CH2tBu)2}5(-N)2(3-N)3] allows access to cubic TaN at 820 ºC (Scheme 1) rather than the thermodynamically expected hexagonal form. [25,26] Scheme 1. Synthesis of TaN determined by the precursor structure.…”

Molecular Nitrides Containing Group 4 and 5 Metals: Single and Double Azatitanocubanes

“…Polynuclear nitrido complexes might be of particular interest as building blocks in the synthesis of metal nitride materials 7. Although the literature precedents are still scarce, Wolczanski and co‐workers have demonstrated that the geometry of the nitridotantalum precursor [( t BuCH 2 ) 2 TaN] 5 ⋅NH 3 ⋅2 C 7 H 8 allows access to cubic TaN at 820 °C, instead of the hexagonal phase, which is more thermodinamically stable at that temperature 5a, 8. Also it is interesting to consider that transition‐metal nitrides produced with laser‐induced plasma reactors are useful systems for studying the molecular details of the change from the gaseous to the condensed state 9.…”

From single-site tantalum complexes to nanoparticles of TaxNy and TaOxNy supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy

“…9(C) ). There is only one report that describes a similar type of NMR observation for such small clusters of tantalum nitride; 57 Wolczansky et al demonstrated that similar types of alkylidene precursors generated clusters/oligomers of amorphous tantalum nitride at temperatures below 673 K and crystalline cubic tantalum nitride at temperatures above 1023 K. They also observed that the 15 N signal corresponding to Ta x N y shifted upfield in the case of small partially amorphous clusters.…”