Reversible Humidity-Driven Transformation of a Bimetallic {EuCo} Molecular Material: Structural, Sorption, and Photoluminescence Studies

Abstract

Functional molecule-based solids built of metal complexes can reveal a great impact of external stimuli upon their optical, magnetic, electric, and mechanical properties. We report a novel molecular material, {[EuIII(H2O)3(pyrone)4][CoIII(CN)6]}·nH2O (1, n = 2; 2, n = 1), which was obtained by the self-assembly of Eu3+ and [Co(CN)6]3– ions in the presence of a small 2-pyrrolidinone (pyrone) ligand in an aqueous medium. The as-synthesized material, 1, consists of dinuclear cyanido-bridged {EuCo} molecules accompanied by two H-bonded water molecules. By lowering the relative humidity (RH) below 30% at room temperature, 1 undergoes a single-crystal-to-single-crystal transformation related to the partial removal of crystallization water molecules which results in the new crystalline phase, 2. Both 1 and 2 solvates exhibit pronounced EuIII-centered visible photoluminescence. However, they differ in the energy splitting of the main emission band of a 5D0 → 7F2 origin, and the emission lifetime, which is longer in the partially dehydrated 2. As the 1 ↔ 2 structural transformation can be repeatedly reversed by changing the RH value, the reported material shows a room-temperature switching of detailed luminescent features including the ratio between emission components and the emission lifetime values.

Optical Phenomena in Molecule-Based Magnetic Materials

“…Moreover, for the case of luminescent molecule-based magnetic materials, additional information should be provided by carefully checking the time stability of the emission signal and the related characteristics, such as the emission lifetime or quantum yield, or even thermometric performance within several cycles of temperature change for optical thermometers. 795,1152,1153 A broad range of optical phenomena are accessible when using luminescent metal complexes or organic molecules in the construction of molecule-based magnetic materials. However, it was found extremely difficult to build a luminescent molecule-based system showing long-range magnetic ordering with T c above even 15 K as most transition metal ions, usually used for high-T c molecular magnets, are not emissive.…”

“…The basic physicochemical characterization before and after the related experiments should be performed to check the preservation of the integrity of the sample after the interaction with light. Moreover, for the case of luminescent molecule-based magnetic materials, additional information should be provided by carefully checking the time stability of the emission signal and the related characteristics, such as the emission lifetime or quantum yield, or even thermometric performance within several cycles of temperature change for optical thermometers. ,, …”

Rational Construction of a Responsive Azo-Functionalized Porous Organic Framework for CO2 Sorption

“…Recently, photoresponsive CO 2 adsorbents have been attracting lots of attention, because the CO 2 adsorption capacity can be adjusted conveniently by light irradiation. As we know, functional materials that respond to different external stimuli, such as redox potential, temperature, pH value, and light, have been developed and used extensively in various applications [ 30 , 31 , 32 , 33 , 34 , 35 ]. The development of sensitive smart materials has become one of the important research areas, because the controllability, rapid responsiveness, and high precision are beneficial in many vital applications.…”