High-temperature, high-pressure hydrothermal synthesis, crystal structure, and solid state NMR spectroscopy of a lead borosilicate with boron-silicon mixing: PbBSiO.

A new lead(ii) borosilicate, PbBSiO (1), has been synthesized by a high-temperature, high-pressure hydrothermal reaction at 480 °C and 990 bar. Its structure was determined by single-crystal X-ray diffraction. The reaction product was phase-pure as indicated by powder X-ray diffraction and whole pattern fitting using the Pawley method. Compound 1 has a 2D layer structure with the lead ions being located at interlayer regions. Each layer is formed of corner-sharing BO or SiO tetrahedra and contains an eight-ring window. The layer consists of a new fundamental building block (FBB) with the formula TO (T: B or Si) formed by two (B(1)Si(1))O tetrahedra and six (Si(2)B(2))O tetrahedra. The FBB can be described as double open-branched triple tetrahedra. Another interesting structural feature of 1 is boron-silicon mixing which is uncommon in borosilicates. There are three unique tetrahedra in the structure: B(1)O tetrahedra with 20% substitution of Si for B, Si(2)O tetrahedra with 6.67% substitution of B for Si, and Si(3)O tetrahedra without substitution. We have applied B and Si MAS NMR spectroscopy to study the substitutional disorder. The NMR study results not only confirm the mixing of B and Si atoms in the structure, but also verify quantitatively the results from single-crystal X-ray diffraction. The reasons for boron-silicon mixing in the structure are discussed. Crystal data for 1: trigonal, R3[combining macron]c (no. 167), a = 9.5090(2) Å, c = 42.3552(8) Å, V = 3316.7(2) Å, Z = 6, R = 0.0147, and wR = 0.0309.