Electron density of orthoboric acid determined by X-ray diffraction at 105 K and ab initio calculations

Abstract

The charge distribution in orthoboric acid, B(OH)3, Mr=61.83, has been investigated experimentally using low-temperature X-ray diffraction data and theoretically by ab initio calculations. Crystal data at 105 K, triclinic, space group P1, a = 7.0187 (14), b = 7.035 (2), c=6.3472 (12) A, a =92.49 (12), /3-- 101.46 (2), 3/=11976(2) °, V= 26290 (1)/~ 3, Z=4, Dx = 1.562 (1) g cm -3, Mo Ka, h = 0.71073/~, /x = 1.51 cm -1, F(000) = 128, R = 0.038 for 3370 observed reflections. The two independent B(OH)3 molecules are identical and planar, each having threefold symmetry. (B-O) = 1.368 (1) ~, (O-B-O) = 120.00 (7) °. The structural parameters for B and O, determined from high-order refinement, are virtually identical to those obtained from a multipole refinement using all the data. The static deformation density in the B-O bonds as determined from a multipole refinement agrees well with the theoretical deformation density obtained from an ab initio calculation beyond the Hartree-Fock level, which had peaks with a density of 0.3 e A-3. The features around the O atoms, especially in the lone-pair regions, agree less well.