High-pressure neutron diffraction studies on laurionite-type Pb(OD)Br

High-pressure neutron diffraction studies on laurionite-type Pb(OD)Br (space group Pnma, Z = 4) were performed at 1, 4 and 8 GPa (wR_p = 5.22, 4.57 and 4.64%, respectively). The decrease of the lattice constants and bond lengths is relatively large for the D...Br (281.0 and 273.6 pm at 1 and 8 GPa, respectively), D...|Pb (313.4 and 295.0 pm), and Pb-Br distances (323.0 and 309.5 pm) and the lattice constant c but very small for the O-D (96.2 and 95.0 pm) and Pb-O distances (241.7 and 239.4 pm). These data reveal that the shape of the Pb²⁺ ion becomes more spherical with increasing pressure and, hence, the hydrogen bond acceptor capability of the lone pair of Pb(II) decreases. Therefore, the strength of the hydrogen bond decreases with increasing pressure as shown from the increase of the OD stretching modes despite the decrease of both the D...Br and D...|Pb hydrogen-bond distances.