Noncentrosymmetric (CHN)(HPO)(HPO)·4HO and Centrosymmetric (CHN)SO·2HO: Exploration of Acentric Structure by Combining Planar and Tetrahedral Motifs via Hydrogen Bonds.

The combination of organic and inorganic nonlinear active units to obtain organic-inorganic hybrid materials has been proved to be a very effective method to obtain nonlinear optical (NLO) materials with excellent properties. Herein we reported two hybrid melamine-based compounds, namely, acentric (CHN)(HPO)(HPO)·4HO () and centrosymmetric (CHN)SO·2HO (), which were synthesized via facile solvent evaporation method. Compound features a three-dimensional (3D) network structure composed of [(HPO)(HPO)(HO)] layers which are further linked with [(CHN)] layers via hydrogen bonds. Compound displays a 3D structure composed of [(CHN)(SO)(HO)] layers further linked with each other by hydrogen bonds. Compound presents a second harmonic generation signal of about 0.1 × KDP. Furthermore, UV-vis and infrared spectra, thermal analyses, and theoretical calculation were also adopted to evaluate its NLO performance. The theoretical calculations showed that the SHG response and large birefringence of were primarily caused by the (CHN), (HPO), and (HPO) groups.