ABSTRACT
BH3 • C4H10N2(5) - BQN(5) + 2CH4(g) + NH3(g) + H2(g) (16) 4. Structure of BCJSl [23,24] and BC2N [7] X-ray powder diffraction patterns of the amine-borane-derived B/C/N materials reveal only (MO) and (00/) diffraction lines, indicating that the materials have graphitic turbostratic structures. Wavelength-dispersive x-ray analysis (WDX) in the scanning electron microscope (SEM) of BQN and BC4N reveals a homo geneous distribution of B, N, and C atoms. Quantitative point analysis by means of electron energy loss spectroscopy (EELS) of BQN in the transmission elec tron microscope (TEM) also suggests the homogeneity of the composition in every part of the material. The boron, carbon, and nitrogen K-edge fine struc tures show i t* features, due to the sp2 character of the elements. Similar results had been obtained by Sasaki et al. [7] for BQN prepared according to reaction (6). Figure 16 shows the ESCA Bl5, Nl5, and Cls spectra for the BQN. Simu lation of the curves for each case, using two or more Gaussian functions suggests the presence of B-C , B-N, C-N, and C -C bonds in BQN. The solid-state 13CMAS-NMR spectrum of the BQN (Fig. 17) exhibits a broad peak with a max imum at 8 = 135 ppm. The chemical shift is in the range of s/?2-hybridized carbon and is hence in accordance with that of poorly crystalline carbon reported by Jarman et al. [26]. The large linewidth is due to the highly disordered nature of the carbon structure and to the random distribution of different carbon bonds (C-B, C-C, C-N) in the material. Reaction (14) and ESCA and NMR analyses suggest the conversion of the piridine-boran-derived polymer into an idealized BQN as shown schematically in Fig. 18 [24]. Attempts of annealing at 2200°C in argon (see Table 3) gave rise to the thermodynamically preferred phases, BN, C, and B12C3, each more crystalline than the unstable graphitic precursor.
