Cs2Mg(H2C3N3S3)4·8H2O: An Excellent Birefringent Material with Giant Optical Anisotropy in π-Conjugated Trithiocyanurate.

Abstract

The design of giant birefringence was performed by adjusting cations to make parallel and compact alignments of π-conjugated (HxC3N3S3)x-3, where x = 1 and 2) groups with large polarizability anisotropy. Finally, the first mixed alkali/alkali-earth-metal trithiocyanurates, A2B(H2C3N3S3)4·nH2O (A = K, Rb, Cs; B = Mg, Sr; n = 5-8, 12), were designed and synthesized successfully. Importantly, Cs2Mg(H2C3N3S3)4·8H2O (III) and K2Sr(H2C3N3S3)4·5H2O (IV) possess large birefringences of 0.580 and 0.194 at 800 nm, respectively, of III has the largest birefringence among all practical birefringent crystals, cyanurates, and hydroisocyanurates.