ASn(C10H12N2O8)Cl·H2O (A = K, Rb): Nonlinear optical crystals with new distorted Sn(IV)-centered nitrogen-oxygen-chloride polyhedron and wide band gaps

Nonlinear optical (NLO) crystals are the core components of laser for their capability of frequency conversion, so it is an important task to develop NLO crystals with excellent performance. Herein, we report two unique NLO crystals containing the Sn(IV) atom, ASn(C10H12N2O8)Cl·H2O (A = K, Rb). Both of them have been rationally synthesized by simultaneously introducing three coordination atoms with different electronegativities into the Sn(IV)-centered polyhedron. The arrangement of distorted [SnO4N2Cl] polyhedrons displays in an ordered phenomenon. They exhibit a phase-matching second-harmonic generation (SHG) response of 0.5 × KDP and wider band gaps than 4.2 eV Remarkably, KSn(C10H12N2O8)Cl·H2O and RbSn(C10H12N2O8)Cl·H2O possess large laser damage thresholds of 177 and 129 MW/cm2, respectively. Systematic studies reveal that the oriented arrangement of the distorted [SnO4N2Cl] polyhedrons makes the main contribution to their SHG response. This research provides an effective method for the exploration of NLO crystals in the future.