Two metal-free cyanurate crystals with a large optical birefringence resulting from the combination of π-conjugated units

By combining the (H x C 3 N 3 O 3 ) x −3 ( x = 0–3) group with the (CN 3 H 6 ) + cation, two metal-free cyanurate birefringent crystals, GU(H 2 C 3 N 3 O 3 ) and GU 3 (H 2 C 3 N 3 O 3 ) 3 (H 3 C 3 N 3 O 3 ), were obtained.