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

Two new bismuth hydroxyl borates, Bi2O2[B3O5(OH)] (I) and Bi2O2[BO2(OH)] (II), have been synthesized under hydrothermal conditions. Their structures were determined by single-crystal and powder X-ray diffraction data, respectively. Compound I crystallizes in the orthorhombic space group Pbca with the lattice constants of a = 6.0268(3) Å, b = 11.3635(6) Å, and c = 19.348(1) Å. Compound II crystallizes in the monoclinic space group Cm with the lattice constants of a = 5.4676(6) Å, b = 14.6643(5) Å, c = 3.9058(1) Å, and β = 135.587(6)°. The borate fundamental building block (FBB) in I is a three-ring unit [B3O6(OH)]4–, which connects one by one via sharing corners, forming an infinite zigzag chain along the a direction. The borate chains are further linked by hydrogen bonds, showing as a borate layer within the ab plane. The FBB in II is an isolated [BO2(OH)]2– triangle, which links to two neighboring FBBs by strong hydrogen bonds, resulting in a borate chain along the a 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)] (II) 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.