Discovery of SrZn₂B₆O₁₂ with an unprecedented quadruple-layered configuration

Exploring new borates with unique structures has been one of the most significant tasks in solid-state chemistry, especially those with layered architecture. In this communication, a new borate, SrZn₂B₆O₁₂, is found to show a quadruple-layered configuration, which has never been found in borate systems. This rare ²[Zn₄B₁₂O_(23+2/3)]_∞ quadruple-layer is stacked by two ²[Zn₂B₆O₁₂]_∞ double-layers that are constructed by two single-layers of ²[B₄O₇]_∞ and ²[Zn₂B₂O₄]_∞. SrZn₂B₆O₁₂ exhibits moderate birefringence and the origin of the optical anisotropy is confirmed by theoretical analysis.