Flexible coordination of Pb atoms and variable zinc–borate frameworks to construct three Pb5Zn4B6O18 polymorphs

Abstract

Three Pb₅Zn₄B₆O₁₈ polymorphs were synthesized by a high temperature solution method. Their structures were determined using single crystal X-ray diffraction and they crystallize in P2₁/c for α-, γ-Pb₅Zn₄B₆O₁₈ and P for β-Pb₅Zn₄B₆O₁₈. It is interesting that α- and β-Pb₅Zn₄B₆O₁₈ crystallize in different space groups with similar structures and α- and γ-Pb₅Zn₄B₆O₁₈ crystallize in the same space group with totally different structures. In α- and β-Pb₅Zn₄B₆O₁₈, ZnO₄ tetrahedra connect with isolated BO₃ triangles to construct two dimensional (2D) layers, while in γ-Pb₅Zn₄B₆O₁₈, 2D Zn–B–O layers change to the 3D framework. The phase transformations of Pb₅Zn₄B₆O₁₈ are investigated by the combination of powder X-ray diffraction, thermal behavior analysis and theoretical simulation. Additional functional properties have been investigated using methods such as including UV-vis-NIR diffuse reflectance and IR spectroscopy.