Syntheses and Crystal Structures of Two New Bismuth Hydroxyl Borates Containing [Bi₂O₂]²⁺ Layers: Bi₂O₂[B₃O₅(OH)] and Bi₂O₂[BO₂(OH)]

Abstract

Two new bismuth hydroxyl borates, Bi₂O₂[B₃O₅(OH)] (<b>I</b>) and Bi₂O₂[BO₂(OH)] (<b>II</b>), have been synthesized under hydrothermal conditions. Their structures were determined by single-crystal and powder X-ray diffraction data, respectively. Compound <b>I</b> crystallizes in the orthorhombic space group <i>Pbca</i> with the lattice constants of <i>a</i> = 6.0268(3) Å, <i>b</i> = 11.3635(6) Å, and <i>c</i> = 19.348(1) Å. Compound <b>II</b> crystallizes in the monoclinic space group <i>Cm</i> with the lattice constants of <i>a</i> = 5.4676(6) Å, <i>b</i> = 14.6643(5) Å, <i>c</i> = 3.9058(1) Å, and β = 135.587(6)°. The borate fundamental building block (FBB) in <b>I</b> is a three-ring unit [B₃O₆(OH)]^4–, which connects one by one via sharing corners, forming an infinite zigzag chain along the <i>a</i> direction. The borate chains are further linked by hydrogen bonds, showing as a borate layer within the <i>ab</i> plane. The FBB in <b>II</b> is an isolated [BO₂(OH)]^2– triangle, which links to two neighboring FBBs by strong hydrogen bonds, resulting in a borate chain along the <i>a</i> direction. Both compounds contain [Bi₂O₂]²⁺ layers, and the [Bi₂O₂]²⁺ layers combine with the corresponding borate layers alternatively, forming the whole structures. These two new bismuth borates are the first ones containing [Bi₂O₂]²⁺ layers in borates. The appearance of Bi₂O₂[BO₂(OH)] (<b>II</b>) completes the series of compounds Bi₂O₂[BO₂(OH)], Bi₂O₂CO₃, and Bi₂O₂[NO₃(OH)] and the formation of Bi₂O₂[B₃O₅(OH)] provides another example in demonstrating the polymerization tendency of borate groups.