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)H-3](2)[NbCl6] was isolated in 68% yield from the same preparation of octachlorotetrakis(cyclohexylphosphine)diniobium(TV). 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 P (1) over bar with a = 9.904(2) Angstrom, b = 10.243 (2) Angstrom, c = 10.642(1) Angstrom, alpha = 76.33(2)degrees, beta = 67.231(8)degrees, gamma = 73.76(2)degrees, V = 945.7(3) Angstrom(3) and Z = 1. Octachlorotetrakis(phenylphosphine)diniobium(IV) crystallizes in the orthorhombic space group Pbca with a = 8.873(2) Angstrom, b = 17.394(6) Angstrom, c = 21.778(3) Angstrom, V = 3361.1(9) Angstrom(3), 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 degrees C. The analysis of the films is presented.