Negative thermal expansion (NTE), whereby lattices contract upon heating, is of considerable interest for its wide applications in many fields. Molecular materials have been widely investigated as catalysts, sensors, etc., which usually endure temperature vibration. NTE can become a substantial means for controlling the coefficients of thermal expansion. Molecular materials possess plentiful structures and can be easily decorated, making them ideal platforms for thermal expansion modification. In this feature article, we provide an overview of the recent developments in utilizing NTE in molecular materials and summarize some mechanisms leading to NTE. The discussion of NTE in molecular materials concerns many factors, including transverse vibration, geometric flexibility, host-guest interactions, spin crossover, molecular packing rearrangement and molecular conformational changes.

Ordered and flexible porous frameworks with solution processability are highly desirable to fabricate continuous and large‐scale membranes for the efficient gas separation. Herein, the first microporous hydrogen‐bonded organic framework (HOF) membrane has been fabricated by an optimized solution‐processing technique. The framework exhibits the superior stability because of the abundant hydrogen bonds and strong π–π interactions. Thanks to the flexible HOF structure, the membrane possesses the unprecedented pressure‐responsive H2/N2 separation performance. Furthermore, the scratched membrane can be healed by the treatment of solvent vapor, achieving the recovery of separation performance.

The control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open-framework structures was investigated. Notably, the presence of guest ions (K ) and molecules (H O) can substantially switch thermal expansion of YFe(CN) from negative (α =-33.67×10 K ) to positive (α =+42.72×10 K )-a range that covers the thermal expansion of most inorganic compounds. The mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X-ray diffraction, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations. The presence of guest ions or molecules plays a critical damping effect on transverse vibrations, thus inhibiting negative thermal expansion. An effective method is demonstrated to control the thermal expansion in open-framework materials by adjusting the presence of guests.

No abstract

On the basis of a rough rule of thumb that the difference in ionic radius for the interstitial cationic pair may affect the structure of some nitride and carbonitride compounds, a novel carbonitride phosphor, YScSiNC:Ce, was successfully designed. The crystal structure (space group P6mc (No. 186), a = b = 5.9109(8) Å, c = 9.67701(9) Å, α = β = 90°, γ = 120°) was characterized by single-crystal synchrotron X-ray diffraction and further confirmed by powder X-ray diffraction and refined with Rietveld methods. Ce-doped YScSiNC shows a broad excitation band ranging from 280 to 425 nm and a broad cyan emission band peaking at about 469 nm upon excitation by near-UV light (400 nm). The mechanism of thermal quenching for this phosphor was also investigated. In addition, a white light-emitting diode (w-LED) was prepared by coating a near-UV chip (λ = 405 nm) with YScSiNC:Ce, β-sialon:Eu (green), and CaAlSiN:Eu (red) phosphors. It emitted a well-distributed warm white light with high color rendering index (CRI) of 94.7 and a correlated color temperature (CCT) of 4159 K. The special color rendering index R12 of the obtained white light was as high as 88. All of the results indicate that this novel phosphor can compensate for the cyan cavity and has potential applications in the full-spectrum lighting field.