2(C3H7N6)+·2Cl−·H2O: an ultraviolet nonlinear optical crystal with large birefrigence and strong second-harmonic generation

An ultraviolet nonlinear optical material benefited from benzene-like planar π-conjugated (C₃N₆) groups, achieved significant balance between large birefringence (Δn = 0.277 at 546 nm) and strong second-harmonic generation intensity ∼4.3 × KDP.