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 (C₃H₇N₆)₆(H₂PO₄)₄(HPO₄)·4H₂O (1) and centrosymmetric (C₃H₇N₆)₂SO₄·2H₂O (2), which were synthesized via facile solvent evaporation method. Compound 1 features a three-dimensional (3D) network structure composed of _∞[(H₂PO₄)₄(HPO₄)(H₂O)₄]^6– layers which are further linked with _∞[(C₃H₇N₆)₆]⁶⁺ layers via hydrogen bonds. Compound 2 displays a 3D structure composed of [(C₃H₇N₆)₂(SO₄)(H₂O)₂]_∞ layers further linked with each other by hydrogen bonds. Compound 1 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 1 were primarily caused by the (C₃H₇N₆)⁺, (H₂PO₄)⁻, and (HPO₄)^2– groups.

中文翻译：

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非中心对称 (C3H7N6)6(H2PO4)4(HPO4)·4H2O 和中心对称 (C3H7N6)2SO4·2H2O：通过氢键结合平面和四面体基序探索无心结构

有机和无机非线性活性单元的组合获得有机-无机杂化材料已被证明是获得具有优异性能的非线性光学（NLO）材料的一种非常有效的方法。在此我们报道了两种基于三聚氰胺的杂化化合物，即无着丝粒(C ₃ H ₇ N ₆ ) ₆ (H ₂ PO ₄ ) ₄ (HPO ₄ )·4H ₂ O ( 1 ) 和中心对称(C ₃ H ₇ N ₆ ) ₂ SO ₄ ·2H ₂ O ( 2)，它们是通过简便的溶剂蒸发法合成的。化合物1具有三维 (3D) 网络结构，由_∞ [(H ₂ PO ₄ ) ₄ (HPO ₄ )(H ₂ O) ₄ ] ^6–层进一步与_∞ [(C ₃ H ₇ N ₆ ) ₆ ] ⁶⁺层通过氢键。化合物2显示由 [(C ₃ H ₇ N ₆ ) ₂ (SO ₄)(H ₂ O) ₂ ] _∞层通过氢键进一步相互连接。化合物1呈现约 0.1 × KDP 的二次谐波生成信号。此外，还采用紫外-可见和红外光谱、热分析和理论计算来评估其 NLO 性能。理论计算表明，SHG响应和1的大双折射主要是由(C ₃ H ₇ N ₆ ) ⁺、(H ₂ PO ₄ ) ^-和(HPO ₄ ) ^2-基团引起​​的。