Flux synthesis and characterization of two barium hydroxyborosilicates with triple and single tetrahedral layers: Ba₂[Si₃B₃O₁₂(OH)] and Ba[Si₂BO₆(OH)]

Two new barium hydroxyborosilicates, Ba₂[Si₃B₃O₁₂(OH)] (1) and Ba[Si₂BO₆(OH)] (2), have been synthesized by a flux method at 480 ​°C and characterized by single-crystal X-ray diffraction and infrared spectroscopy. Both compounds have 2D layer structures. Compound 1 contains planar slabs of borosilicate formed of tetrahedral building units which can be described as condensation of three 3-connected 2D single layers with a 6³ network topology. The Ba²⁺ cations are located in both the interlayer and intralayer regions. The structure is unusual with respect to the triple tetrahedral layers. Compound 2 consists of very contorted (3,4)-connected single layers with the rare (4².6²)(4.6²)₂ topology. The single layer is composed of both tertiary and quaternary tetrahedra. The synthesis method is new. A mixture of Ba(OH)₂·8H₂O, H₃BO₃ and SiO₂ was sealed in a gold ampoule, heated at high temperature in a pressure vessel, and the flux is a small amount of concentrated aqueous hydroxide solution. Crystal data for compound 1: monoclinic, P2₁/n, a ​= ​4.7112(2) Å, b ​= ​29.9482(14) Å, c ​= ​7.3773(4) Å, β ​= ​92.593(2)°, V ​= ​1039.81(9) ų, Z ​= ​4, and R1 ​= ​0.0246; compound 2: monoclinic, P2₁/c, a ​= ​7.4206(2) Å, b ​= ​8.9405(2) Å, c ​= ​8.5677(2) Å, β ​= ​90.208(1)°, V ​= ​568.41(2) ų, Z ​= ​4, and R1 ​= ​0.0467.