A highly birefringent metal-free crystal assembled by cooperative non-covalent interactions

By the cooperation of non-covalent interactions, we designed a metal-free birefringent crystal, NH 4 (H 2 C 6 N 7 O 3 )·2H 2 O, which possesses high birefringence Δ n (exp) = 0.54@550 nm for effective modulation of polarized light.