Three New Niccolites: High‐Temperature Phase Transitions, Prominent Anisotropic Thermal Expansions, Dielectric Anomalies, and Magnetism

Metal ion modulation triggers dielectric double switching and green fluorescence in A2MX4-type compounds

Multifunctional switching materials show great potential for applications in sensors, smart switches, and other fields due to their ability to integrate different physical channels in one single device. However, multifunctional responsive materials with multiple switching and luminescence properties have rarely been reported. Here, we report three organic-inorganic hybrids: [TMAA]₂[CoCl₄] (compound 1), [TMAA]₂[CdBr₄] (compound 2) and [TMAA]₂[MnCl₄] (compound 3). Compound 1 and compound 2 undergo two reversible phase transitions at high temperature (328.95/359.25 K and 350.45/393.15 K, respectively). Since the inorganic skeleton has a strong influence on the luminescence properties of such structured substances, Cd and Co were replaced with Mn, after which compound 3 was obtained as expected. The above strategy triggered bright green luminescence with a quantum yield of 35.19%, and significantly increased the phase transition temperature of compound 3 to above 400 K. The above results show that the regulation of the inorganic skeleton provides a new strategy for researchers to develop dual phase change/luminous materials.

Multiple rotor modes and how to trigger them: complex cation ordering in the family of relaxing hybrid formates

A combination of structural, dielectric and calorimetric studies is used to describe a highly atypical behaviour of novel hybrid formate [NH₃(CH₂)₃NH₂(CH₂)₃NH₃][Mn(HCOO)₃]₃, incorporating large triprotonated molecular cations. Two successive phase transitions, switching between fast multiple rotor modes, and the surprising probable coexistence of static and dynamic disorder are discussed for this compound.

Stepwise Dielectric Switching Occurs in Two Photo-Responsive Complexes Possessing Two-Dimensional Structures

Two organic-inorganic hybrid complexes, (CH₃NH₃)Na[Fe(CN)₅NO]·H₂O (1) and (CH₃NH₃)₂[Fe(CN)₅NO] (2), which exhibit stepwise dielectric switching as well as photo-induced structural transformation, are synthesized and examined. In these two compounds, the photo-responsive complex anions, [Fe(CN)₅NO]^2-, connected by Na⁺ through N-Na coordination bonds or CH₃NH₃⁺ through N···H-N hydrogen bonds, form two-dimensional structures. One organic cation, CH₃NH₃⁺, that resides in the intralaminar cavity and plays a role as a template, undergoes a temperature-controlled order-disorder structural phase transition. As the frozen-thawed state change of the polar organic cations modifies the polarizability of materials, stepwise dielectric switching is observed at the phase transition temperature. Furthermore, the photo-induced linkage isomerism of [Fe(CN)₅NO]^2- building block survives in the new compounds at the low-temperature range, which is verified by variable-temperature IR spectra after photo-irradiation. The coexistence of switchable dielectric properties and photo-induced structural variation suggests multiple optical-electric roles of the present materials.

Halogen regulation triggers NLO and dielectric dual switches in hybrid compounds with green fluorescence

An effective strategy of using halogens to modify organic–inorganic hybrid materials to obtain NLO switching characteristics, which is expected to be used for the directional adjustment of NLO switch activity.

Role of the B′-site metal ion in the framework structures and dielectric transitions in host–guest type cyanometalates (HIm)2[B′Co(CN)6] (HIm = imidazolium cation)

The B′-site alkali metal ion in (HIm)₂[B′Co(CN)₆] plays a key role in the change of the framework structures and the dynamic behaviours of the guest.