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IR and 29 Si, 11 B, and 15 N NMR-spectroscopic data of 15 N-enriched samples of hexamethyldisilazane, 1,1,1-trichloro-3,3,3-trimethyldisilazane (TTDS), 1,1,1-trichloro-3,3,3-trimethyldisilazane (TTDS), ((trichlorosilyl)amino)dichloroborane (TADB), of the poly(borosilazane) Si 3 B 3 N 7.9 H 4.4 Cl 0.8 O 0.6 , and of the ceramical network Si 3 B 3 N 7 are given. The 15 N-substituted samples have been prepared using novel synthetic routes. The NMR data show that in the poly(borosilazane) Si 3 B 3 N 7.9 H 4.4 Cl 0.8 O 0.6 silicon is coordinated tetrahedrally by nitrogen in the first coordination sphere and boron is coordinated trigonally planar by nitrogen atoms. In this partially polymerized network, a small fraction of the nitrogen coordination is blocked by hydrogen, as verified by IR spectroscopy. Calcination of the poly(borosilazane) results in the fully polymerized network Si 3 B 3 N 7 . The local coordination of silicon and boron remains virtually unchanged. As confirmed by comparison of the NMR data of Si 3 B 3 N 7 with those of crystalline references (Si 3 N 4 , BN), nitrogen is now fully coordinated by three silicon and/or boron atoms.

The synthesis and polymerization of Cl 2 MeSi-NH-BCl 2 (MADB) and ClMe 2 Si-NH-BCl 2 (DADB) is reported. MADB and DADB are obtained in two-step reaction sequences from MeSiCl 3 , Me 3 Si-NH-SiMe 3 (HMDS), and BCl 3 (/ MADB) or Me 2 SiCl 2 , HMDS and BCl 3 (/ DADB). The monomeric single source precursors are structurally characterized by means of NMR and IR spectroscopy and mass spectrometry. The molecular structure of DADB is additionally investigated by single crystal X-ray diffraction. It crystallizes orthorhombically in space group Pbca with a ¼ 1334.4 pm, b ¼ 1375.4 pm, c ¼ 1607.8 pm, and Z ¼ 8. In the solid state two molecules are associated via intermolecular B-N coordination, forming planar B 2 N 2 rings with almost identical B-N bond lengths. Polymerization of MADB and DADB is performed by ammonolysis and aminolysis (MeNH 2 ) releasing MADB-NH, DADB-NH, MADB-NMe, and DADB-NMe as colorless solids (MADB-NH) or colorless viscous liquids. The viscosity increases with increasing cross-linking density from DADB-NMe to MADB-NMe to DADB-NH. Accordingly, ceramic yields decrease from 77% (MADB-NH) to 45% (DADB-NH) to below 30% DADB-NMe). As-obtained ceramics are fully amorphous. Their near-range order is investigated using solid state 11 B, 13 C, and 29 Si NMR spectroscopy. All materials display BN 3 coordination at boron whereas the bonding situation at silicon is different. Silicon atoms in DADB-NH have 'mixed' SiN x C y (x + y ¼ 4) environments, whereas the 29 Si NMR spectra of MADB-NMe and DADB-NMe suggest SiN 4 coordination. High temperature TGA performed in a He atmosphere up to 2000 C indicates that DADB-NH ceramics are most stable; the onset of decomposition is above 1900 C. SiC and Si 3 N 4 reflections in the XRD patterns of the heated samples indicate that partial crystallization occurs during the heat treatment at elevated temperature.

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