Li Wencong, Wang Junbo, Liu Lili, Huang Chunmei, Ding Yanyan, Zhu MengMeng, Tian Jindan, Qi Haixin, Chu Yaoqing, Xu Jiayue
Institute of Crystal Growth, School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418, China.
Chongqing Key Laboratory of Inorganic Functional Materials, College of Chemistry, Chongqing Normal University, Chongqing 401331, China.
Inorg Chem. 2024 May 6;63(18):8408-8417. doi: 10.1021/acs.inorgchem.4c00844. Epub 2024 Apr 22.
Planar π-conjugated groups, like CO, NO, and BO triangles, are ideal functional units for designing birefringent materials due to their large optical anisotropy and wide band gap. The key point for designing birefringent crystals is to select appropriate functional building blocks (FBBs) and the proper arrangement mode. It is well known that the substitution strategy has proven to be a promising and accessible approach. In this work, alkali metals were chosen to regulate and control two different π-conjugated groups, CO and NO, to build new compounds with large birefringence. Subsequently, three new compounds, NaK(CO)(NO)X·6HO (X = NO, Cl, Br), were successfully synthesized using the hydrothermal method. The aliovalent substitution between the [NO] anionic group and halogen anions [Cl]/[Br] has been achieved in these compounds. NaK(CO)(NO)X·6HO feature the well-coplanar CO and NO groups in their crystal structure. This coplanar arrangement mode may effectively enhance the anisotropic polarizability of NaK(CO)(NO)X·6HO. And their experimental birefringence can reach 0.094-0.131 at 546 nm. Diffuse reflectance spectra demonstrate that these compounds exhibit short ultraviolet (UV) absorption edges of ∼235 nm. Meanwhile, NaK(CO)(NO)X·6HO also have an easily grown capacity under facile conditions. This work not only reports three new potential UV birefringent crystals but also provides a strategy to make the π-conjugated MO group coplanar.
平面π共轭基团，如CO、NO和BO三角形，由于其大的光学各向异性和宽带隙，是设计双折射材料的理想功能单元。设计双折射晶体的关键在于选择合适的功能结构单元（FBBs）和适当的排列方式。众所周知，取代策略已被证明是一种有前景且可行的方法。在这项工作中，选择碱金属来调控两种不同的π共轭基团CO和NO，以构建具有大双折射的新化合物。随后，采用水热法成功合成了三种新化合物NaK(CO)(NO)X·6H₂O（X = NO、Cl、Br）。在这些化合物中实现了[NO]阴离子基团与卤素阴离子[Cl]/[Br]之间的异价取代。NaK(CO)(NO)X·6H₂O在其晶体结构中具有共面性良好的CO和NO基团。这种共面排列方式可能有效增强NaK(CO)(NO)X·6H₂O的各向异性极化率。并且它们在546 nm处的实验双折射可达0.094 - 0.131。漫反射光谱表明这些化合物在约235 nm处呈现短紫外（UV）吸收边。同时，NaK(CO)(NO)X·6H₂O在简便条件下也具有易于生长的能力。这项工作不仅报道了三种新的潜在紫外双折射晶体，还提供了一种使π共轭MO基团共面的策略。
