LADDER STRUCTURE OF [(TBUCH2)2TAN]5.NH3.2C7H8 AND ITS RELATIONSHIP TO CUBIC TAN

Ammonolysis of (tBuCH2)3Ta=CHtBu (1) at 20 °C produced an intermediate pentamer, [(tBuCH2)2TaN]5 (2, ∼40%); further reaction generated an orange precipitate. Thermolysis of the latter at 400 °C and then 820 °C produced cubic TaN (Fm3m, a = 4.300 (2) Å) at temperatures and pressures substantially below those of conventional nitriding procedures. Ammonolysis of (tBuCH2)2Ta(NMe2)3 (3) provided an alternative (19%), route to 2. 1H, 13C, and 15N NMR spectra of 2 indicated C2v symmetry, and X-ray crystallographic characterization of [(tBuCH2)2TaN]5·NH3·2C7H8 (2·NH3·2C7H8) revealed a roughly planar ladder structure of alternating (tBuCH2)2TaN units. The interior nitrogens adopt a T-shaped coordination geometry and an NH3 is weakly bound to an exterior Ta atom. Crystal data (2·NH3·2C7H8): triclinic P1, λ(Mo Kα), μ = 7.068 mm-1, a = 11.616 (2) Å, b = 15.407 (3) Å, c = 23.172 (6) Å, α = 106.120 (17)°, β = 99.060 (18)°, Γ = 100.170 (16)°, T = -20 °C, Z = 2, V= 3829.6 (12) Å3, R = 0.083, Rw = 0.098, 7346 (72.8%) reflections where |F0| ≥ 3σ(F0). The conformation of 2·NH3·2C7H8 reflects the motif of cubic TaN, rather than the thermodynamically expected hexagonal form, hence the framework of this ceramic may be dictated by the geometry of the molecular precursor. © 1990, American Chemical Society. All rights reserved.