In the field of structural chemistry, crystals containing the [OM4] tetrahedra (M = metal cation) structure have been well documented. However, compounds containing both [OPb4] tetrahedra and pi-conjugated groups are less reported due to their structural complexity. In this work, a new lead borate-nitrate, Pb9O4(BO3)2(NO3)4, has been synthesized by a high temperature melt method. Notably, the structure of Pb9O4(BO3)2(NO3)4 contains special [O8Pb18]infinity chains formed by the [OPb4] tetrahedra. This compound possesses a large optical anisotropy with birefringence of Delta n = 0.117 at 546 nm.

Ionic liquids are regarded as green solvents mainly due to their non-volatile and easy regeneration and recycling properties. However, ionic liquids have negative effects on the environment and human health, especially alkyl imidazole ionic liquids are more toxic than traditional organic solutions. Studies on the toxicology, ecotoxicology, and degradation of ionic liquids are rarely found in the literature. Here, we prepared the cheap La and Ce-codoped TiO2@PAM (polyacrylamide) composite microspheres with a simple procedure for the first time to degrade three kinds of imidazole ionic liquids with high efficiency. The experimental results show that the composite La (0.25%) and Ce (0.15%)-codoped TiO2@PAM composite microspheres with calcination temperature of 450 °C had a high photocatalytic activity for 1-butyl-3-methyl imidazolium hexafluorophosphate, 1-hexyl-3-methyl imidazolium hexafluorophosphate, and 1-octyl-3-methyl imidazolium hexafluorophosphate with the concentration of 10 mg/L. The photocatalysis degradation extent of the three ionic liquids is 97.4, 91.2, and 88.5% at 90 min. This work opened a new route for the simple preparation of cheap composite microspheres in the photocatalytic degradation of ionic liquids with a high efficiency.

The exploration of crystal materials for optical manipulation by nonlinear optical (NLO) and anisotropic light-matter interaction is of paramount importance in modern science and technology. However, in such crystal materials, finding the right balance between second harmonic generation (SHG), birefringence, and the bandgap presents a significant challenge. In this contribution, we employ extended octupolar pi-conjugated groups devoid of intrinsic dipole moments to construct melonate-based inorganic-organic hybrid crystals, thereby achieving simultaneous large optical nonlinearity and anisotropy. In accordance with this strategy, Rb3[C6N7(NCN)3]3H2O (I) and Cs3[C6N7(NCN)3]3H2O (II) were obtained and subjected to detailed investigation. Strong SHG responses of similar to 9x KH2PO4 and a large birefringence of at least 0.6@546 nm were observed for I and II crystals, respectively, together with a suitable bandgap for visible-UV application. Theoretical calculations indicated that octupolar [C6N7(NCN)3]3- groups of I and II arranged in a near parallel configuration exhibit a discrete pi electron distribution, resulting in enhanced NLO susceptibilities and maximal polarizability difference. This work underscores the potential of octupolar structures with extended pi-conjugation as a promising avenue for the discovery of NLO and birefringence crystals.

AbstractCombining π‐conjugated and non‐π‐conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non‐π‐conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π‐conjugated [C4N3H6] groups. The resulting organic–inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546 nm), and blue‐violet and green fluorescence near 360 and 520 nm, respectively. This work expands the methodology for creating new NLO crystals through organic–inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material.

Investigating ultraviolet (UV) birefringent crystals is a focal point of research in recent years. The development of superior birefringent materials faces substantial challenges, primarily due to the need to pinpoint optimal fundamental building blocks and to perfect their geometric arrangement within the crystal lattice. By selecting a planar pi-conjugated [C(NH2)3] group and a staggered [S2O6] group, we have successfully synthesized an organic-inorganic hybrid crystal, [C(NH2)3]2S2O6. Similar to the famous inorganic crystal Sr2Be2B2O7 (SBBO), [C(NH2)3]2S2O6 exhibits a two-dimensional double-layered crystal structure connected by N-HO hydrogen bonding. Due to the ideal spatial arrangements of the planar pi-conjugated [C(NH2)3] group, this crystal displays a large birefringence (0.150 at 546 nm) among sulfate derivatives in the short-wave UV region. Meanwhile, [C(NH2)3]2S2O6 has a large band gap of 5.23 eV. This work indicates that the [S2O6] unit, acting as a direct structural motif, is beneficial for the discovery of UV birefringent crystals.

The investigation of birefringent materials is predominantly focused on pi-conjugated systems; however, a large band gap or deep ultraviolet (DUV) transmittance cannot be guaranteed. In this work, we propose an extended pi-conjugated strategy to increase the birefringence while keeping the large band gap. In the scheme, two new fluoroaluminoborates, BaAlB3O6F2 and BaAl2(B3O6)(2)F-2, are synthesized by combining the [BO3] group with the [AlO4F2] group and the [B3O6] group with the [AlO3F] group through a rational structural design. The experimental results indicate that both BaAlB3O6F2 and BaAl2(B3O6)(2)F-2 exhibit shorter UV cutoff wavelengths (<200 nm) and larger birefringence (Delta n > 0.07@546 nm). Notably, this is a new finding in the Ba-Al-B-O-F system since the discovery of the well-known nonlinear optical crystal BaAlBO3F2. In comparison with BaAlBO3F2, BaAlB3O6F2 and BaAl2(B3O6)(2)F-2 exhibit a markedly elevated birefringence (0.0418 vs. 0.087/0.105 at 546 nm). Furthermore, BaAl2(B3O6)(2)F-2 exhibits the largest band gap (7.87 eV) of all known F-containing aluminoborates. This work not only identifies two potential DUV birefringent materials, but also proposes a novel design approach for reconciling the conflicting properties between birefringence and bandgap.

A new melamine sulfamate crystal with large birefringence and wide band gap was synthesized by combining π-conjugated group and non-π-conjugated group.

Owing to diverse crystal structures and intriguing properties, metal phosphates have attracted much attention in recent studies. In this work, two cadmium phosphates, KCd6P7O24 and KCd3P3O11, were obtained by the high-temperature solution method. In the crystal structure, both the title compounds contain two types of P-O fundamental building units. Thermal and spectral analyses were carried out on the title compounds, indicating that both of them have good thermal stability and short UV cut-off edges. In addition, the relationship between the electronic structures and optical properties was studied by theoretical calculations.

Fluorine-containing borate crystal materials are particularly attractive due to their rich structural chemistry and excellent properties for optical applications. In this work, a new compound Ba3.75MgB7O14F2.5 has been synthesized through the high-temperature solution method. In the crystal structure of Ba3.75MgB7O14F2.5, the [B7O14] basic building unit and the [MgO3F3] octahedra are interconnected to create a complex three-dimensional network. The structural feature of the less commonly observed [B7O14] units is discussed, and it has been found that such units in Ba3.75MgB7O14F2.5 are most conducive to achieving large birefringence. In addition, Ba3.75MgB7O14F2.5 exhibits good thermal stability, a short ultraviolet cutoff of 203 nm, and large birefringence (0.081@546 nm), indicating its potential as a new UV birefringent crystal.

Nonlinear optical (NLO) crystals are very important for laser technology, but the performances of available NLO crystals are still insufficient for increasing demand. Recently, the exploration of new NLO crystals in non-π-conjugated systems with the heteroatomic tetrahedra is attracting a lot of interest. In this work, we systematically explore the metal sulfamates containing [NH2SO3] groups and four metal sulfamates, namely, Ca(NH2SO3)2·4H2O, Ca(NH2SO3)2·H2O, Pb(NH2SO3)2·H2O, and Pb(NH2SO3)2 were synthesized by aqueous solution and hydrothermal methods. Notably, these metal sulfamates exhibit different crystal structures and optical properties owing to the diverse arrangement of the functional groups in their structures. In addition, due to hydrogen bond regulation, the centrosymmetric (CS) compound Ca(NH2SO3)2·4H2O can transform into noncentrosymmetric (NCS) Ca(NH2SO3)2·H2O, leading to NLO activity. Experimental characterizations and theoretical analysis reveal that these metal sulfamates are ultraviolet transparent and suitable for developing new NLO materials.