Na4Sn4(C2O4)3F6 and NaSnC2O4F·H2O: two tin(ii) fluoride oxalates display large birefringence†
Abstract
Birefringent materials play an important role in laser techniques as an essential part of optical devices. Therefore, the exploration of high-performance birefringent materials has been a central focus of researchers. Herein, two tin(II) fluoride oxalates Na4Sn4(C2O4)3F6 and NaSnC2O4F·H2O were gained by the combination of birefringence-active groups of Sn2+ with stereochemically active lone pairs and planar π-conjugated [C2O4]2− groups. These groups assemble into low-dimensional structures of 0D [C2O4F4]6− clusters and 1D [SnC2O4F]∞− chains in Na4Sn4(C2O4)3F6, and double [Sn2(C2O4)2F2]∞2− chains in NaSnC2O4F·H2O, which gives rise to the large birefringence of 0.160@546 nm and 0.189@546 nm, respectively. Detailed structure–property analysis and theoretical calculations indicate that strong optical anisotropy can be induced by the rational arrangement of the Sn2+-polyhedra and [C2O4]2− groups.
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