POLYAMIDOIMIDONITRIDE CLUSTERS OF ZIRCONIUM

Nitrogen-based polyoxoanion analogues that contain nitride (N3-), and amide (NH2-), and amide (NH2-) ligands have been prepared via ammonolysis of (tritox)Zr(CH2Ph)3 (1). Cluster formation is apparently directed by the steric bulk of tritox (tBu3CO-). Treatment of 1 with 1.0 equiv of NH3 in benzene for approximately 5 days at 25-degrees-C provided colorless crystals of a approximately 0.6:1.0 composite of pseudooctahedral, C2 [(tritox)Zr]6(mu-6-N)(mu-3-NH)6(mu-2-NH2)3 (2) and square pyramidal [(tritox)Zr]5(mu-5-N)(mu-3-NH)4(mu-2-NH2)4 (3), according to X-ray studies and H-1, C-13 {H-1], and crucial N-15 NMR investigations. A cross-polarization magic angle spinning (CPMAS) N-15 NMR spectrum of the crystals verified their composition. Addition of 1.75 equiv of NH3 to benzene solutions of 1 at 25-degrees-C generated pure, colorless crystals of 3 (32%), whose structure was determined by X-ray crystallography: orthorhombic, Pbca, a = 15.554 (3) angstrom, b = 25.804 (5) angstrom, c = 40.406 (8) angstrom, Z = 8, V = 16217 (5) angstrom 3, T = 293 K, R = 11.3%, R(w) = 11.2%, GOF = 1.77 for 3729 reflections (data-to-parameter = 8.6:1) with [F(o)[ greater-than-or-equal-to 3-sigma(F(o)). Exposure of 1 to 2.6 equiv of NH3 or treatment of 3 with excess ammonia produced the dodecaamido cluster [(tritox)Zr]5(mu-5-N)(mu-2-NH2)12 (4). In solution, 4 was observed in equilibrium with 3 and 4.0 equiv of NH3. The cluster cores are related to simple cubic lattices, and the N-15 NMR shifts of the mu-N6 (2, delta -40.6) and mu-N5 (3, delta -62.6; 4, delta -6.5) ligands are comparable to that of cubic ZrN (CPMAS N-15 NMR: delta -20).