Polyhedral structure representations. (a) The model structure for β-Zn(OH)2 developed during this work. (b) M(OH)2·H2O, i.e. α-M(OH)2. (c) An LDH phase with x = 0.333. The spheres represent M2+ (grey), M3+ (blue), O2− (red), C4+ (black), H+ (pink) and the O atoms of water molecules (brown). Lattice parameters and atomic coordinates are given in Table 1 for the β-Zn(OH)2 and Tables 2 and 3 for the model LDH phases. All structures are drawn to the same scale (a scale bar is inset in Fig. 3a). The structures are all viewed along b with c up the page. A unit cell for β-Zn(OH)2 is outlined in Fig. 3(a): the length of the vertical line is c and the horizontal line is a cos (30). For the LDH phases, the layer spacing, c′, and the thickness of the main layer, h(oct), i.e. the distance between the two planes of O atoms that form the octahedral layer, are indicated in Fig. 3(b).