Conversion of [(<SUP>t</SUP><SUP></SUP>BuCH<INF>2</INF>)<INF>2</INF>TaN]<INF>5</INF> to Cubic TaN:  Related Syntheses, EHMO Calculations, and MAS and Spin Echo <SUP>15</SUP>N NMR Spectroscopies

The conversion of pentamer [(^tBuCH<INF>2</INF>)<INF>2</INF>TaN]<INF>5</INF> (<BO>2</BO>) and ammonia to cubic TaN<INF>0.8</INF> (<BO>5</BO>) proceeds via precipitate 1/n[TaC<INF>1.41</INF>H<INF>3.90</INF>N<INF>1.90</INF>]<INF>n</INF><INF></INF> (<BO>3</BO>) and amorphous TaN (<BO>4</BO>). Precursors other than (^tBuCH<INF>2</INF>)<INF>3</INF>Ta&dbd;CH^tBu (<BO>1</BO>) and NH<INF>3</INF>, which provided <BO>2</BO>, such as Ta(NMe<INF>2</INF>)<INF>5</INF> (<BO>7</BO>) and NH<INF>3</INF>, (Me<INF>2</INF>N)<INF>3</INF>Ta&dbd;N^tBu (<BO>9</BO>) and NH<INF>3</INF>, also afforded <BO>5</BO>. Extended Hückel molecular orbital calculations were conducted to examine the electronic changes that appear upon oligomerization of hypothetical Me<INF>2</INF>TaN to (Me<INF>2</INF>TaN)<INF>∞</INF>, as a model for pentamer <BO>2</BO> formation. The relationship between pentamer <BO>2</BO> and the remaining nitrides, <BO>3</BO>−<BO>5</BO> 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 Ta<INF>2</INF>N<INF>2</INF> “squares” of the pentamer (<BO>2</BO>) and the 3-dimensional Ta<INF>4</INF>N<INF>4</INF> “cubes” of the ultimate product, cubic TaN<INF>0.8</INF> (<BO>5</BO>).