Synthesis, Structure, and Chemical Vapor Deposition Studies of Molecular Precursors to NbP Films

Treatment of niobium pentachloride with cyclohexylphosphine and phenylphosphine in dichloromethane afforded
octachlorotetrakis(cyclohexylphosphine)diniobium(IV) (85%) and octachlorotetrakis(phenylphosphine)diniobium(IV) (88%), respectively, as brown-red and dark red crystalline solids. In addition, the phosphonium compound
[P(C6H11)H3]2[NbCl6] was isolated in 68% yield from the same preparation of octachlorotetrakis(cyclohexylphosphine)diniobium(IV). Studies are described which demonstrate that the primary phosphine serves as the
hydrogen atom source for the formation of the phosphonium salts. Octachlorotetrakis(cyclohexylphosphine)diniobium(IV) can be prepared in 77% yield by addition of cyclohexylphosphine to NbCl4(THF)2 in toluene. The
X-ray crystal structure determinations for two dimeric niobium(IV) complexes are described. Octachlorotetrakis(cyclohexylphosphine)diniobium(IV) crystallizes in the triclinic space group P1̄ with a = 9.904(2) Å, b = 10.243(2) Å, c = 10.642(1) Å, α = 76.33(2)°, β = 67.231(8)°, γ = 73.76(2)°, V = 945.7(3) Å3, and Z = 1.
Octachlorotetrakis(phenylphosphine)diniobium(IV) crystallizes in the orthorhombic space group Pbca with a =
8.873(2) Å, b = 17.394(6) Å, c = 21.778(3) Å, V = 3361.1(9) Å3, and Z = 4. Octachlorotetrakis(cyclohexylphosphine)diniobium(IV) and octachlorotetrakis(phenylphosphine)diniobium(IV) were evaluated as
molecular precursors to niobium(III) phosphide (NbP) films in a chemical vapor deposition reactor. Octachlorotetrakis(phenylphosphine)diniobium(IV) was not volatile and was therefore not a useful precursor. However,
octachlorotetrakis(cyclohexylphosphine)diniobium(IV) afforded specular, silver-colored films of NbP with substrate
temperatures between 400 and 600 °C. The analysis of the films is presented.