Sn2B7O12F with a 2∞[B14O24]6− layer constructed from the unprecedented [B7O16]11− fundamental building block

Abstract

A new tin borate fluoride Sn₂B₇O₁₂F has been successfully synthesized by the high-temperature solution method in a closed system. It crystallizes in the monoclinic space group C2/c. The structure features a new fundamental building block (FBB) [B₇O₁₆]¹¹⁻, which further condenses to an infinite ²_∞[B₁₄O₂₄]⁶⁻ layer extended in the ab plane. The adjacent layers are bridged by the unique isolated [Sn₄O₁₂F₂]¹⁸⁻ clusters, which are constructed from two [Sn₂O₇F]¹¹⁻ polyhedra sharing a common edge. First-principles calculations have shown that the birefringence of Sn₂B₇O₁₂F is about 0.07@1064 nm, which originated from the the synergistic contributions of the B–O and Sn–O/F interactions.