Ba₃(C₃N₃O₃)₂: A New Phase of Barium Cyanurate Containing Parallel π-Conjugated Groups as a Birefringent Material Replacement for Calcite

Finding Short-Wavelength Birefringent Crystals with Large Optical Anisotropy Activated by π-Conjugated [C(NH2)3] Units

“…Studies have shown that the birefringence is the macroscopic representation of optical polarizability in their microscopic groups, and thus the optical anisotropy polarizability of a unit is considered to be the main source of birefringence in related crystals . According to this, several systems can be regarded as the optimized ones to find high performance birefringent materials, such as crystals with π-conjugated [BO 3 ], − [CO 3 ], − [NO 3 ], and [H x C 3 N 3 O 3 ] ( x = 0, 1, 2) units, − in which the embodied π electrons are the intrinsic factor of large optical anisotropy polarization. When the above units are further polymerized, even a great enhancement of optical anisotropy can be achieved.…”

“…In recent years, more crystals with four-coordinated units, such as [BO x F 4– x ] ( x = 0–4), ,− , [PO 3 F], − [PO x S 4– x ] ( x = 0–4), and [SiO x N 4– x ] ( x = 0–4), , are reported to have enlarged birefringence when compared with their pure oxidized tetrahedra. This can be well-explained by the positive roles of F/N/S atoms on reducing the symmetry of original units to enhance the optical polarization anisotropy and birefringence. ,− Even though, to be as a birefringent material, the π-conjugated system has more competitiveness when compared with non-π-conjugated ones. ,,− ,− …”

Cs3Na(H2C3N3O3)4·3H2O: A Mixed Alkali‐Metal Hydroisocyanurate Nonlinear Optical Material Containing π‐Conjugated Six‐Membered‐Ring Units

“…According to the UV/Vis‐IR reflectance spectra (Figure a), 1 has a high transmittance (80 %) in the wavelength above 290 nm and a wide transparency window covering from the near IR to UV spectral range. The UV absorption edge of 1 is 227 nm, corresponding to the band gap of 5.46 eV, which is comparable to those of Ba 3 (C 3 N 3 O 3 ) 2 (5.14 eV), KLHCY (5.23 eV), K 2 (HC 3 N 3 O 3 ) (4.95 eV),[18b] Ba 2 Mg(C 3 N 3 O 3 ) 2 (5.20 eV), and K 6 Cd 3 (C 3 N 3 O 3 ) 4 (5.23 eV) …”

Zn(H2C3N3O3)2·3H2O: the first single-d10transition metal based ultraviolet hydroisocyanurate crystal with large birefringence

“…The newly discovered anion group of (H x C 3 N 3 O 3 ) x−3 (x = 0-3), which is similar to the (B 3 O 6 ) 3− group, has shorter interatomic distances, more uniform distribution of p electrons, stronger p π -p π conjugated interaction, and greater anisotropy compared to the (B 3 O 6 ) 3− group, indicating that the plane π-conjugated group (H x C 3 N 3 O 3 ) x−3 (x = 0-3) is an excellent structural unit for increasing the birefringence. 17,18 Recently, many cyanurates with alkali metals and alkali earth metals possessing large birefringence have been reported, such as Ba 3 (C 3 N 3 O 3 ) 2 (Δn cal = 0.32 at 800 nm, λ UV = 241 nm), 19 20 and K(H 3 C 3 N 3 O 3 )(NO 3 ) (Δn exp = 0.253 at 546.1 nm, λ UV = 228 nm). 21 However, most of the alkali metals and alkali earth metals are very air sensitive, which hinders their possible applications under extreme conditions in high-temperature and humid environments.…”