CONVERSION OF [((T)BUCH(2))(2)TAN](5) TO CUBIC TAN - RELATED SYNTHESES, EHMO CALCULATIONS, AND MAS AND SPIN-ECHO N-15 NMR SPECTROSCOPIES

The conversion of pentamer [((t)BuCH(2))(2)TaN](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)BuCH(2))(3)Ta=CH(t) Bu (1) and NH3, which provided 2, such as Ta(NMe(2))(5) (7) and NH3, ( Me(2)N)(3)-Ta=N(t)Bu (9) and NH3, also afforded 5. Extended Huckel mol ecular orbital calculations were conducted to examine the electronic c hanges that appear upon oligomerization of hypothetical Me(2)TaN to (M e(2)TaN)(infinity), as a model for pentamer 2 formation. The relations hip between pentamer 2 and the remaining nitrides, 3-5 was probed via magic angle spinning (MAS) and spin-echo solid-state N-15 NMR experime nts that probe the local environments of the various nitrogen atoms. I n combination with N-15-labeling studies, the spin-echo spectra were u sed in an effort to analyze the possibility of a direct relationship b etween the 2-dimensional Ta2N2 ''squares'' of the pentamer (2) and the 3-dimensional Ta4N4 ''cubes'' of the ultimate product, cubic TaN0.8 ( 5).