The transformation of a zero-dimensional cluster into a one-dimensional chain structure achieving a dramatically enhanced birefringence in tin(ii)-based oxalates

Abstract

Developing new birefringent materials with large optical anisotropy is extremely urgent due to the fantastic progress of laser science and technology. Here, two tin(II)-based oxalates, K₂Sn(C₂O₄)₂·H₂O and K₂Sn₂(C₂O₄)₂F₂·H₂O, were successfully synthesized by simultaneously introducing π-conjugated [C₂O₄]²⁻ groups and distorted Sn²⁺-polyhedra with stereochemically active lone pairs. The use of F⁻ regulates the arrangement of birefringence-active groups, resulting in the transformation of zero-dimensional (0D) K₂Sn(C₂O₄)₂·H₂O into 1D K₂Sn₂(C₂O₄)₂F₂·H₂O, which successfully enhances birefringence from 0.103@546 nm to 0.301@546 nm. Meaningfully, detailed structural and property analysis demonstrates that the ideal spatial arrangement of all the birefringence-active functional modules can induce strong optical anisotropy, providing an idea for designing birefringent materials with excellent properties.