Preparation and characterization of molybdenum and tungsten nitride nanoparticles obtained by thermolysis of molecular precursors

作者：Dezelah CL; El Kadri OM; Heeg MJ; Winter CH^*

来源：Journal of Materials Chemistry, 2004, 14(21): 3167-3176.

DOI：10.1039/b405636a

Treatment of Mo((NBu)-Bu-t)(2)Cl-2 with [K(Ph(2)pz)(THF)](6) (pz=pyrazolyl) in tetrahydrofuran afforded Mo((NBu)-Bu-t)(2)(Ph(2)pz)(2) (85%), while treatment of W((NBu)-Bu-t)(2)((NHBu)-Bu-t)(2) with 3,5-diphenylpyrazole afforded W((NBu)-Bu-t)(2)(Ph(2)pz)(2) (97%). The complexes M((NBu)-Bu-t)(2)(Ph(2)pz)(2) were characterized completely by spectral and analytical data, and by an X-ray crystal structure determination for Mo((NBu)-Bu-t)(2)(Ph(2)pz)(2). Thermolysis of M((NBu)-Bu-t)(2)(Ph(2)pz)(2) at 800degreesC under nitrogen afforded 2-3 nm metal nitride nanoparticles that were embedded in an amorphous carbon-oxygen matrix, as determined by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. X-Ray photoelectron spectroscopy also revealed the presence of metal oxide phases, which were amorphous by X-ray powder diffraction. The nanoparticles prepared at 800degreesC were insoluble. Thermolysis of M((NBu)-Bu-t)(2)(Ph(2)pz)(2) at 425degreesC afforded amorphous 2-3 nm nanoparticles, as determined by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. X-Ray photoelectron spectroscopy suggested a molybdenum(IV) nitride and W2N/WN, as well as MoO3 and an oxidized tungsten nitride. Materials prepared at 425degreesC were not embedded in a matrix, and were soluble in tetrahydrofuran. Infrared and NMR spectroscopy suggested the presence of surface organic fragments that contain alkyl-substituted phenyl groups. Such surface groups are most likely derived from decomposition of the heterocyclic ligands. Simultaneous differential thermal analysis/thermogravimetric analysis indicated that the amorphous nitride materials convert to crystalline nanoparticles consistent with M2N phases between 600-700degreesC, along with a weight loss that may correspond to dinitrogen evolution. The amorphous carbon-oxygen matrix also forms upon heating from 425 to 800degreesC. This work provides the first description of tungsten nitride nanoparticles, as well as the first description of soluble group 4-6 nanoparticles.

• 出版日期2004