Preparation, Structural Characterization, and Thermal Ammonolysis of Two Novel Dimeric Transition Silylamide Complexes

Abstract

The preparation and molecular structures of two novel dimeric transition metal silylamide complexes fLi 0.5 Zr[NHSi(NMe 2 ) 3 ] 1.5 [NSi(NMe 2 ) 3 ] 0.5 [m-NSi(NMe 2 ) 3 ]g 2 and fLi 0.5 Hf[NHSi(NMe 2 ) 3 ] 1.5 [NSi(NMe 2 ) 3 ] 0.5 [m-NSi(NMe 2 ) 3 ]g 2 with a tetrahedral coordination environment are reported. Thermal ammonolysis of fLi 0.5 Zr[NHSi(NMe 2 ) 3 ] 1.5 [NSi(NMe 2 ) 3 ] 0.5 [m-NSi(NMe 2 ) 3 ]g 2 in an autoclave yields a mesoporous partially lithiated silicon zirconium imide powder Si 3 Zr(N)(NH) x (NH 2 ) y (NMe 2 ) z with a surface area of 440 m 2 /g. A microporous partially lithiated silicon hafnium imide powder Si 3 Hf(N)(NH) x (NH 2 ) y (NMe 2 ) z with a surface area of 232 m 2 /g was obtained via a similar ammonolysis process of fLi 0.5 Hf[NHSi (NMe 2 ) 3 ] 1.5 [NSi(NMe 2 ) 3 ] 0.5 [m-NSi(NMe 2 ) 3 ]g 2 . Both of these silicon zirconium and hafnium imide powders have a disordered octahedral coordination environment. Pyrolysis of these zirconium and hafnium silicon imide powders leads to the formation of mixtures of porous zirconium or hafnium lithium silicon nitride ceramics with a regular octahedral coordination environment. They contain some residual lithium and exhibit a much reduced surface area due to an almost total collapse of the pores during the pyrolysis process.

Synthesis and processing of silicon nitride and related materials using preceramic polymer and non-oxide sol-gel approaches

“…This was insoluble, but was treated under ammonia at 160 °C and 15 Bar to produce a mixed imide that could be fired at 1000 °C to make a titanium nitride-silicon nitride composite. Zirconium and hafnium analogues were also produced by a similar route [33]. It is noteworthy that, whilst this is elegant chemistry, the precursors are complex, their high molecular weights often result in insolubility, they may not retain their bonded structures during decomposition and the silicon to heteroatom ratios are defined by the precursor and so are inflexible in terms of product composition.…”