Na2PbB6O10SO4 and Ca2.58Pb0.42B6O11SO4: first borate–sulfates featuring 3D porous borate anionic frameworks

Abstract

This study presents two new borate–sulfate compounds, Na₂PbB₆O₁₀SO₄ (I) and Ca_2.58Pb_0.42B₆O₁₁SO₄ (II). Both crystals form unique three-dimensional (3D) porous frameworks ³[B6O10]_∞ and ³[B7O13]_∞, composed of fundamental building blocks [B₆O₁₃] and [B₇O₁₇], respectively, with [SO₄] units embedded within the pores. These examples represent the first observation of 3D borate frameworks in borate–sulfates, thus expanding the structural diversity of borate–sulfate compounds. The relationship between the structure and birefringence was studied using first-principles calculations. This study uncovers new insights into the connectivity and structural properties of borate–sulfates.