Syntheses and crystal structures of the α- and β-forms of zinc orthoborate, Zn3B2O6

The low-temperature α-form and the high-temperature β-form of Zn3B2O6 have been prepared by solid-state reactions. The X-ray structural analysis showed that α-Zn3B2O6 crystallizes in a triclinic space group P1¯ with a = 6.302(2) Å, b = 8.248(1) Å, c = 10.020(1) Å, α = 89.85(1)°, β = 89.79(1)°, γ = 73.25(1)°, Z = 4 and β-Zn3B2O6 in a monoclinic group C2/c with a = 23.840(1) Å, b = 5.049(1) Å, c = 8.388(1) Å, β = 102.905(9)°, Z = 8. α-Zn3B2O6 represents a new structure type in which ZnO4 tetrahedra are connected to each other and also to BO3 triangles by common corners giving rise to a three-dimensional framework, while β-Zn3B2O6 is characterized by a three-dimensional network built from corner- and edge-sharing ZnO4 tetrahedra as well as corner-sharing ZnO4 tetrahedra and BO3 triangles. It is the difference in the orientation of the BO3 groups as well as the variation of the connection modes of ZnO4 groups that is responsible for the structural differences between α- and β-Zn3B2O6.