Hydrothermal Growth of Lanthanide Borosilicates: A Useful Approach to New Acentric Crystals Including a Derivative of Cappelenite

The reaction of barium borosilicate glasses in hydrothermal fluids with NaOH mineralizer at ca. 600–650 °C in the presence of various sources of Eu3+ ions leads to a new series of noncentrosymmetric single crystals characterized by single-crystal X-ray diffraction. Under three slightly different reaction modifications, three new Eu3+-containing noncentrosymmetric single crystals were isolated and characterized. Using a barium borosolicate glass with Eu2O3 added to the reaction mixture led to NaBaEuSi3O9 (1), which crystallizes in the noncentrosymmetric orthorhombic space group P212121 with unit cell parameters a = 5.6373(11) Å, b = 11.483(2) Å, and c = 12.535(2) Å and consists of Eu3+ ions linked by Si3O96– rings. Using a similar glass feedstock with Eu3+ included in the starting glass composition led to the compound NaBa3Eu3Si6O20 (2), which was determined in the noncentrosymmetric polar space group Ama2 with unit cell parameters a = 14.777(3) Å, b = 23.926(5) Å, and c = 5.5533(11) Å. It is constructed of individual islands of Si4O1310– and lone Si2O76– building fragments. Finally, use of the Eu-containing glass along with additional Eu2O3 led to the compound BaEu6(Si3B6O24)­(OH)2 (3), which crystallizes in the polar space group P6mm with a = 10.8074(15) Å and c = 4.7296(9) Å. It is related to the rare and poorly understood mineral cappelenite Ba­(Y,RE)6(Si3B6O24)­F2 and contains six-membered tetrahedral borate rings linked by silicate tetrahedra. The high percentage of noncentrosymmetric crystals obtained from of a simple borosilicate glass starting material, along with various straightforward chemical additives, suggests strongly that many more noncentrosymmetric crystals can be isolated from this general system.