The First Positive Uniaxial Cyanurate Crystals Containing a Crown-like Anionic Group Arrangement and Strengthened Optical Anisotropy

Two new alkali/alkali earth metal and d(10) transition metal mixed cyanurate birefringent crystals, Li2Zn2(H2C3N3O3)(2)(HC3N3O3)(OH)(2)center dot 2H(2)O (I) and BaZn2(H2C3N3O3)(2)-(HC3N3O3)(OH) (2)center dot 2H(2)O (II), were synthesized by a mild hydrothermal method. Both I and II crystals belong to the tetragonal I4(1)/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-) (A(I)) and [(H2C3N3O3)(4)(HC3N3O3)(4)](12-) (A(II)), forming A(I)A(II)for all(II)for all(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 pi-conjugated systems.

Automated summary

Two new mixed cyanurate birefringent crystals were synthesized using a mild hydrothermal method, showcasing a unique crystalline structure and a large band gap. Theoretical calculations suggested their potential application as ultraviolet birefringent polarizers and for optical anisotropy modulation in other pi-conjugated systems.