Chinese Journal of Structural Chemistry最新文献

An organic-inorganic hybrid antimony(III) oxalate (C₅H₆ON)₂[Sb₂O(C₂O₄)₃] has been successfully obtained by simultaneous combination of π-conjugated 4-hydroxypyridine and (C₂O₄)^2– group with stereochemical active Sb(III) cation. The compound features a layered structure, and the equatorial planes of SbO₆ units, π-conjugated (C₂O₄)^2– and (C₅H₆ON)⁺ groups are closer to a planar arrangement, representing strong structural anisotropy that favors a large birefringence. As expected, (C₅H₆ON)₂[Sb₂O(C₂O₄)₃] exhibits a large birefringence of 0.279 at 546 nm. Structural and theoretical analyses indicate that the combination of multiple π-conjugated units is a feasible approach for designing and exploring new superior birefringent materials.

In the realm of molecular phase transition research, particularly for applications in sensors, data storage and switching technologies, the role of organic-inorganic hybrid perovskite materials has been increasingly recognized for their significant potential. Nevertheless, hybrid post-perovskites, as a critical subclass of perovskites, have not been thoroughly studied and mainly limit in the instances based on polyatomic bridging agents like dicyanamide (dca⁻) and non-cyclic organic cations. Herein, a polar cyclic quaternary ammonium cation, N,N-dimethylpyrrolidinium (DMP⁺), was used to assemble a new hybrid post-perovskite, (DMP)[Mn(dca)₃] (1), which undergoes a phase transition from orthorhombic Bmmb to monoclinic P2₁/n space group at 249 K. By employing multiple techniques such as differential scanning calorimetry, variable-temperature single-crystal X-ray analysis, dielectric measurements, and Hirshfeld surface analysis, we disclosed the role of polar cyclic quaternary ammonium DMP⁺ in elevating the phase-transition temperature by 48 K, generating significant dielectric switching effect and facilitating interlayer sliding of inorganic framework.

Materials exhibiting dielectric switching response and photoluminescence (PL) are promising for sensors and information storage. In previous research, we synthesized a series of materials with red or green PL and dielectric switching capabilities by incorporating luminescent metal halides into organic ammonium compounds. However, effective modification to synthesize organic-inorganic hybrid materials with dielectric switching response and orange PL continues to be a challenge in the respective fields. Orange PL materials are valuable for switching and sensors, and most orange light sources are derived from rare earth elements, making them harder to obtain. We have successfully synthesized two organic-inorganic hybrid materials ([CMPD]PbBr₃ (1) and [BMPD]PbBr₃ (2), CMPD = N-ClCH₂-N-methylpiperidine, BMPD = N-BrCH₂-N-methylpiperidine) that exhibit both orange PL and dielectric switching response. When Cl in compound 1 is substituted by Br in compound 2, the phase transition temperature of the compound is elevated by 45 K. These compounds exhibit captivating orange light emission when exposed to ultraviolet lamps. This research provides insights into exploring multifunctional materials with orange PL and dielectric switching response and provides proof for halogen substitution strategies to design materials with higher phase transition temperatures.

Two-dimensional (2D) lead halide perovskites have attracted tremendous attention due to their outstanding physical properties. However, the presence of toxic lead is a major problem for large-scale applications. Here, we report the synthesis, phase transition, dielectric and photoluminescence (PL) properties of a lead-free 2D Ge-based perovskite (BIM)₂GeI₄ (BIM = benzimidazolium) which experiences a phase transition at 405 K accompanied by an order-disorder change of organic spacer. Moreover, the step-like dielectric transition near the phase transition temperature makes it suitable for dielectric switching. Meanwhile, (BIM)₂GeI₄ has a direct bandgap of 2.23 eV and broadband emission from 550 to 1000 nm, implying its unique optical property for potential near-infrared lighting and displaying. This work provides a fresh example for the development of lead-free 2D Ge-based perovskite with potential applications in the fields of optoelectronics and high temperature dielectric switching.

Hybrid organic-inorganic perovskites (HOIP) have attracted increasing interest in the last decade. While current research in this field focuses on metal halide HOIPs because of their excellent photovoltaic and optoelectronic properties, other hybrid perovskites are also being designed and developed for other properties. Among them, HOIPs bridged by nitrate show structural diversity and a remarkable range of physical properties. In this mini review, we summarize their structural features and rich physical properties including structural phase transitions, ferroelectric, piezoelectric, piezomagnetic and photoluminescencent properties. In addition, the challenges for improving the physical properties achieved by such materials and the space for further development of such materials are also discussed.