The crystal structures of two new Ba borates: pentaborate hydrate, Ba[B5O8(OH)]center dot H2O, and decaborate, LiBa2[B10O16(OH)(3)]

Two new Ba berates, Ba[B5O8(OH)]H2O (I) and LiBa2[B10O16(OH)(3)] (II), were synthesized in the hydrothermal systems Cs2CO3-BaO-B2O3-H2O (T = 550 K, P = 100 bar, 20 days). The crystal structures of I and II were established fr om X-ray single crystal diffraction; I, space group P-1, a = 6.785(5), b = 6.831(5), c = 10.629(6) Angstrom, alpha = 100.07(4), beta = 91.98(6), gamma = 119.46(7)degrees V = 417.01(58) Angstrom(3), R-hkl = 0.069 for 1328Fo>4 sigma(Fo); II, space group P-1, a = 6.732(1), b = 11.369(2), c = 11.581(2) Angstrom, alpha = 119.31(3), beta = 90.11(3), gamma = 73.08(3)degrees, V = 728.87(42) Angstrom(3), R-hkl = 0.048 for 1166Fo greater than or equal to 4 sigma(Fo). The topology of the berate sheet of phase I is practically the same as that in the monoclinic structure of biringuccite, Na-2[B5O8(OH)].H2 O. The gaps between the sheets in synthetic Ba-biringuccite contain Ba atom s and water molecules. Phase LT is characterized by a new boron sheet, form ed by five crystallographically independent BO4 tetrahedra and by five BO3 triangles. (C) 2000 Elsevier Science S.A. All rights reserved.