¹¹B NMR Study of WB₂

Abstract

The structure of tungsten diboride, WB 2 , differs from those of metal diborides with AlB 2 -or ReB 2 -type structures that have been previously studied by 11 B NMR spectroscopy. As opposed to the single 11 B resonance reported for the metal diborides having those AlB 2 -or ReB 2 -type structures, four groups of 11 B resonances are found for WB 2 . There is also 11 B NMR spectral evidence to support the proposal by Kiesling in 1947 of an additional boron atom at the center of some of the sixmembered boron rings. The 11 B quadrupolar frequencies of all four groups of resonances in WB 2 are all quite small (<20 kHz), in keeping with the trend observed for 11 B in metal diborides having the AlB 2 -structure as the metal is taken from further down the groups (families) in the periodic table.

Synthesis and characterization of aluminum diboride products using 27Al, 11B NMR and ab initio studies

“…This was followed by 11 B studies of ReB 2 [8] and WB 2 [9]. The experimental NMR details are discussed in depth in these studies.…”

“…The experimental NMR details are discussed in depth in these studies. In particular, the 11 B quadrupolar frequencies, m Q , at 275 kHz for ReB 2 and even less for WB 2 , are small enough [9] for the radio frequency (RF) pulse to excite the full 11 B resonance, including the satellite transitions. Such considerations are important in spin-lattice relaxation measurements.…”

Progress in functional studies of transition metal borides*

“…So far, three crystal structures of WB 2 were reported in the experiment, Mo 2 B 5 -type (R-3m), AlB 2 -type (P6/mmm), and W 2 B 4 -type (P63/mmc). [31][32][33][34][35][36][37][38][39][40][41] However, the phonon calculations suggested the AlB 2 -type WB 2 is dynamically unstable and was predicted to be a stable high-pressure phase above 65 GPa. [33] Another controversy is the stoichiometric ratio of W 2 B 5 .…”