Hydrothermal growth of lanthanide borosilicates: a useful approach to new acentric crystals including a derivative of cappelenite.

Abstract

The reaction of barium borosilicate glasses in hydrothermal fluids with NaOH mineralizer at ca. 600-650 °C in the presence of various sources of Eu(3+) 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 Eu(3+)-containing noncentrosymmetric single crystals were isolated and characterized. Using a barium borosolicate glass with Eu(2)O(3) added to the reaction mixture led to NaBaEuSi(3)O(9) (1), which crystallizes in the noncentrosymmetric orthorhombic space group P2(1)2(1)2(1) with unit cell parameters a = 5.6373(11) Å, b = 11.483(2) Å, and c = 12.535(2) Å and consists of Eu(3+) ions linked by Si(3)O(9)(6-) rings. Using a similar glass feedstock with Eu(3+) included in the starting glass composition led to the compound NaBa(3)Eu(3)Si(6)O(20) (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 Si(4)O(13)(10-) and lone Si(2)O(7)(6-) building fragments. Finally, use of the Eu-containing glass along with additional Eu(2)O(3) led to the compound BaEu(6)(Si(3)B(6)O(24))(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)(Si(3)B(6)O(24))F(2) 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.