Orthoborate halides with the formula (M~(+II))_5(BO _3)_3X: Syntheses, crystal structures and Raman spectra of Eu_5(BO_3)_3Cl and Ba_5(BO _3)_3X (X = Cl, Br)

摘要

Single crystals of Eu_5(BO_3)_3Cl were obtained by serendipity by reacting Eu_2O_3 and Mg with B_2O_3 at 1300 K in the presence of an NaCl melt for 13 h in silica-jacketed Nb ampoules. Ba_5(BO_3)_3X (X = Cl, Br) crystals were formed by direct synthesis from appropriate amounts of Ba(OH)_2, H_3BO_3 and the respective barium halide (hydrate) in alumina crucibles kept in the open atmosphere at 1300 K for 13 h. The crystal structures of the title compounds were determined with single-crystal X-ray diffraction. All compounds crystallize isotypically to Sr_5(BO_3)_3Cl in the orthorhombic space group C222_1 (no. 20, Z = 4) with the lattice parameters a = 1000.34(7), b = 1419.00(9), c = 739.48(5) pm for Eu_5(BO_3)_3Cl, a = 1045.49(5), b = 1487.89(8), c = 787.01(4) pm for Ba_5(BO _3)_3Cl, and a = 1048.76(7), b = 1481.13(9) and c = 801.22(5) pm for Ba_5(BO_3)_3Br. The Raman spectra of all compounds were acquired and are presented and compared to literature data. The incremental volume of the orthoborate (BO_3)~(3-) anion has been determined and is compared to the Biltz volume.