Bismuth Borates: One-Dimensional Borate Chains and Nonlinear Optical Properties

Three bismuth borates, Bi[B4O6(OH)2]OH (I), BiB2O4F (II), and Bi3[B6O13(OH)] (III), were obtained in boric acid flux at low temperatures and their structures were determined by using single-crystal and powder X-ray diffraction techniques. All these three bismuth borates contain one-dimensional borate chains and crystallize in noncentrosymmetric space groups. I is a hydrated borate, crystallizing in the space group P1 with lattice constants a = 4.300(1) Å, b = 8.587(2) Å, c = 10.518(2) Å, α = 113.11(3)°, β = 100.50(3)°, and γ = 90.36(3)°, and the borate chain consists of a 3-ring (2BO3 + BO4) and a BO3 group. II is a fluoroborate, which crystallizes in the trigonal space group P32 with a = 6.7147(1) Å and c = 6.4688(1) Å, and the borate anion is a 3-fold helix chain formed by extensive linkage of three-membered borate rings (3BO4). III is also a hydrated borate with a structure that is closely related to II, in which one-sixth of the borate groups are in triangular geometry (BO3), which reduces the symmetry to P1, a = 6.6257(1) Å, b =6.6238(1) Å, c = 6.6541(1) Å, and α = 89.998(3)°, β = 89.982(2)°, and γ = 119.992(2)°. All these three bismuth borates exhibit nonlinear optical (NLO) properties.