From BiF3 to BiF3·H2O: diverse Bi(iii) coordination for structural transformation and birefringence regulation

Abstract

Lone pair activity is an important factor to regulate the crystal structure symmetry and related optical response. Herein, a new type of hydrated bismuth fluoride, BiF₃·H₂O, was synthesized and characterized by a facile hydrothermal reaction. Obviously, the introduction of a water molecule significantly changed the coordination environment of Bi³⁺, thereby seriously changing the crystal structure of the compound BiF₃. Compared with asymmetric BiF_m fundamental building blocks in other compounds, BiF₃·H₂O possesses unprecedented near-isotropic BiF₉ polyhedra and exhibits regulated birefringence values. Therefore, this work will contribute to the structural diversity of Bi_mF_n-based compounds and explore the development of new birefringent crystals.