Cs₃Na(H₂C₃N₃O₃)₄·3H₂O: A Mixed Alkali‐Metal Hydroisocyanurate Nonlinear Optical Material Containing π‐Conjugated Six‐Membered‐Ring Units

Abstract

Practical ultraviolet nonlinear optical (NLO) crystals are indispensable in modern scientific equipment and solar‐blind communication systems. Herein, a new hydroisocyanurate NLO crystal, Cs 3 Na(H 2 C 3 N 3 O 3 ) 4 · 3H 2 O ( 1 ), was grown by a facile aqueous solution method. It features a two‐dimensional layered structure composed of coplanar large π‐conjugated 2 ∞ [H 2 C 3 N 3 O 3 ] – isocyanurate ribbons. More importantly, it exhibits concurrently short ultraviolet phase‐matching capability (λ pm ≈ 227 nm) and considerable second‐harmonic‐generation response (d eff ≈ 2/3 KDP) resulting from the π‐conjugated (H 2 C 3 N 3 O 3 ) – six‐membered ring units. First principles calculations were employed to elaborate its delocalized π‐bonds and strong interaction between the Cs + cations and (H 2 C 3 N 3 O 3 ) – anionic groups. Consequently, 1 will be a promising ultraviolet NLO material for the fourth harmonic generation of Nd‐based lasers. Successful synthesis of the title compound also provides a new roadmap to discover new ultraviolet linear optical or NLO materials in metal hydroisocyanurates.