Crystal structure, electric field gradient, and electronic charge densities in ReB2: A single crystal x-ray, B11 nuclear magnetic resonance, and first-principles study

Abstract

We have grown a single crystal of ReB2 and refined its crystal structure. Our structural studies confirmed the hexagonal structure (space group P 63 /mmc) with lattice parameters a=2.8982 (1) Å and c=7.4723 (3) Å. We also report the observation of first order satellites in the B 11 nuclear magnetic resonance, which indicated the presence of a nonzero quadrupole coupling frequency, νQ =276±3 kHz, and an asymmetry parameter η=0 at the boron atom sites. These values are in excellent agreement with electric-field-gradient (EFG) tensor calculations based on first principles. These calculations showed that the principal axis of the most negative EFG-tensor component, VZZ, is parallel to the c -axis of the crystal. This behavior is in agreement with the observed excess of B pz charge (c direction) over the px and py charges and is related to stronger metal-boron bonds compared to previously studied YB12 and LaB6, where the B-B bonds are stronger. Finally, the bonding properties of ReB2 are discussed in terms of densities of states, valence-electron densities, and partial charges. © 2009 American Institute of Physics.