The First Positive Uniaxial Cyanurate Crystals Containing a Crown-like Anionic Group Arrangement and Strengthened Optical Anisotropy
Dandan Wang, Fei Liang, Xinyuan Zhang, Zhanggui Hu, Yicheng Wu
Abstract
Two new alkali/alkali earth metal and d10 transition metal mixed cyanurate birefringent crystals, Li2Zn2(H2C3N3O3)2(HC3N3O3)(OH)2·2H2O (I) and BaZn2(H2C3N3O3)2(HC3N3O3)(OH)2·2H2O (II), were synthesized by a mild hydrothermal method. Both I and II crystals belong to the tetragonal I41/a space group which is rarely seen in metal cyanurates and feature the novel zero-dimensional crown-like clusters composed of [(H2C3N3O3)4(HC3N3O3)6]16– (AI) and [(H2C3N3O3)4(HC3N3O3)4]12– (AII), forming AIAII∀II∀I shape links due to the existing mirror symmetry. The UV–vis–NIR diffuse reflectance spectrum showed a large band gap of I (5.21 eV). Notably, theoretical calculations illustrated that I and II are the first two positive uniaxial cyanurate crystals due to the crown-like arrangement of standing cyanurate anionic groups. This work promotes I and II as promising ultraviolet birefringent polarizers and a feasible approach for optical anisotropy modulation in other π-conjugated systems.