A Highly Stable Microporous Calcium-Based MOF for C2H2/CO2 Separation with Low Regenerative Energy.

Most of the porous materials used for acetylene/carbon dioxide separation have the problems of poor stability and high energy requirements for regeneration, which significantly hinder their practical application in industries. Here, we report a novel calcium-based metal-organic framework (NKM-123) with excellent chemical stability against water, acids, and bases. Additionally, it has exceptional thermal stability, retaining its structural integrity at temperatures up to 300 °C. This material exhibits promising potential for separating C2H2 and CO2 gases. Furthermore, it demonstrates an adsorption heat of 29.3 kJ mol-1 for C2H2, which is lower than that observed in the majority of MOFs used for C2H2/CO2 separations. The preferential adsorption of C2H2 over that of CO2 is confirmed by dispersion-corrected density functional theory (DFT-D) calculations. In addition, the potential of industrial feasibility of NKM-123 for C2H2/CO2 separation is confirmed by transient breakthrough tests. The robust cycle performance and structural stability of NKM-123 during multiple breakthrough tests show great potential in the industrial separation of light hydrocarbons.

Reticular synthesis of 8-connected carboxyl hydrogen-bonded organic frameworks for white-light-emission.

The rational design and construction of hydrogen-bonded organic frameworks (HOFs) are crucial for enabling their practical applications, but controlling their structure and preparation as intended remains challenging. Inspired by reticular chemistry, two novel blue-emitting NKM-HOF-1 and NKM-HOF-2 were successfully constructed based on two judiciously designed peripherally extended pentiptycene carboxylic acids, namely H8PEP-OBu and H8PEP-OMe, respectively. The large pores within these two HOFs can adsorb fluorescent molecules such as diketopyrrolopyrrole (DPP) and 9-anthraldehyde (AnC) to form HOFs ⊃ DPP/AnC composites, subsequently used in the fabrication of white-light-emitting devices (WLEDs). Specifically, two WLEDs were assembled by coating NKM-HOF-1 ⊃ DPP-0.13/AnC-3.5 and NKM-HOF-2 ⊃ DPP-0.12/AnC-3 on a 330 nm ultraviolet LED bulb, respectively. The corresponding CIE coordinates were (0.29, 0.33) and (0.32, 0.34), along with corresponding color temperatures of 7815 K and 6073 K. This work effectively demonstrates the feasibility of employing reticular chemistry strategies to predict and design HOFs with specific topologies for targeted applications.

Reticular Modulation of Piezofluorochromic Behaviors in Organic Molecular Cages by Replacing Non-Luminous Components.

Organic piezochromic materials that manifest pressure-stimuli-responses are important in various fields such as data storage and anticounterfeiting. The manipulation of piezofluorochromic behaviors for these materials is promising but remains a great challenge. Herein, a non-luminous components regulated strategy is developed and organic molecular cages (OMCs), a burgeoning class of crystalline organic materials with structural dynamics, are first explored for the design of piezofluorochromic materials with tunable luminescence. A series of OMCs based on aggregation-induced emission (AIE) chromophores, termed Cage 1-3, are synthesized and their piezofluorochromic behaviors are investigated by diamond anvil cell technique. Due to the sufficient voids between its flexible chromophores offered by the OMC structure, Cage 1 exhibits thermofluorochromic and piezofluorochromic properties. Moreover, the piezofluorochromic performance of this OMC could be further promoted by replacing its non-luminous components with improved flexibilities, and a remarkable luminescence peak shift by 150 nm together with a response sensitivity of 13.8 nm GPa-1 was achieved upon hydrostatic compression. The cage structure plays a vital role in facilitating efficient and reversible piezofluorochromic behaviors. This study has shed light on the rational design and exploitation of OMCs as an exceptional platform to accomplish customizable piezofluorochromic behaviors and enlarge their potential applications in pressure-based luminescence.

A High Working Temperature Multiferroic Induced by Inverse Temperature Symmetry Breaking.

Molecular-based multiferroic materials that possess ferroelectric and ferroelastic orders simultaneously have attracted tremendous attention for their potential applications in multiple-state memory devices, molecular switches, and information storage systems. However, it is still a great challenge to effectively construct novel molecular-based multiferroic materials with multifunctionalities. Generally, the structure of these materials possess high symmetry at high temperatures, while processing an obvious order-disorder or displacement-type ferroelastic or ferroelectric phase transition triggered by symmetry breaking during the cooling processes. Therefore, these materials can only function below the Curie temperature (Tc), the low of which is a severe impediment to their practical application. Despite great efforts to elevate Tc, designing single-phase crystalline materials that exhibit multiferroic orders above room temperature remains a challenge. Here, an inverse temperature symmetry-breaking phenomenon was achieved in [FPM][Fe3(µ3-O)(µ-O2CH)8] (FPM stands for 3-(3-formylamino-propyl)-3,4,5,6-tetrahydropyrimidin-1-ium, which acts as the counterions and the rotor component in the network), enabling a ferroelastoelectric phase at a temperature higher than Tc (365 K). Upon heating from room temperature, two-step distinct symmetry breaking with the mm2Fm species leads to the coexistence of ferroelasticity and ferroelectricity in the temperature interval of 365-426 K. In the first step, the FPM cations undergo a conformational flip-induced inverse temperature symmetry breaking; in the second step, a typical ordered-disordered motion-induced symmetry breaking phase transition can be observed, and the abnormal inverse temperature symmetry breaking is unprecedented. Except for the multistep ferroelectric and ferroelastic switching, this complex also exhibits fascinating nonlinear optical switching properties. These discoveries not only signify an important step in designing novel molecular-based multiferroic materials with high working temperatures, but also inspire their multifunctional applications such as multistep switches.

Linker Flexibility-Dependent Cluster Transformations and Cluster-Controlled Luminescence in Isostructural Silver Cluster-Assembled Materials (SCAMs).

Silver chalcogenolate clusters (SCCs) and silver cluster-assembled materials (SCAMs) are an important category of novel luminescent materials, the emission of which can be modulated by variation of the cluster nodes and linker species. Here, the successfully synthesis of two isostructural 2D SCAMs is reported: Ag12 bpa and Ag12 bpe are formed by using two linkers with different conformational freedom (bpa=1,2-bis(4-pyridyl)ethane, bpe=1,2-bis(4-pyridyl)ethylene), with dodenuclear silver chalcogenolate clusters as secondary building units (SBUs). Interestingly, nonluminescent Ag12 bpa at room temperature could quickly transform into 1D Ag10 bpa, with concomitant dissociation of two silver atoms and the remaining ten silver atoms rearranging in the cluster, thus exhibiting an intense yellow phosphorescence after being triggered by acetonitrile (CH3 CN). Similarly, stimulating Ag12 bpe with CH3 CN, by contrast, gave another 2D structure Ag12 bpe-1b with the distorted SBUs and different topology structure, and both of them are merely red-emissive at low temperature. To note, after exchanging ligands, room-temperature nonluminescent 2D Ag12 bpe-1b can be transformed into intensely luminescent 1D Ag10 bpa. This linker-flexibility-dependent structural transformation and cluster-based SBU controlled luminescence remains scarce. Our work provides new insights into structure-luminescence relationship in clustered metal-organic frameworks and intelligent stimulus-responsive luminescent materials.

New stable isomorphous Ag34 and Ag33Au nanoclusters with an open shell electronic structure.

A novel atom-precise 3-electron homosilver nanocluster (Ag34) has been assembled for the first time by the oxidation of a thiol. When adding AuPPh3Cl in the reaction, we obtained an alloyed Ag33Au nanocluster, which shares a similar framework as that of Ag34, in which a doping Au atom replaced a core silver atom. Notably, both Ag34 and alloyed Ag33Au demonstrated exceptional stability in solution and solid state over 3 months, which is difficult to explain by using the superatom model. Such Ag34 and Ag33Au complexes complement the nanoclusters with an open shell electronic structure and unveil a new approach to synthesize monodisperse nanoclusters under mild conditions.

Encapsulating [Mo3S13]2- clusters in cationic covalent organic frameworks: enhancing stability and recyclability by converting a homogeneous photocatalyst to a heterogeneous photocatalyst.

We encapsulated anionic [Mo3S13]2- clusters in cationic COFs (EB-COF) to obtain the novel composite photocatalytic material Mo3S13@EB-COF. Comprehensive studies indicated that the Mo3S13@EB-COF was the product of a successful conversion of a homogeneous to a heterogeneous catalyst, and exhibited excellent stability and recyclability as well as a remarkable photocatalytic hydrogen evolution rate of 13 215 µmol g-1 h-1 under visible-light irradiation over the course of 18 hours.

Layer-sliding-driven crystal size and photoluminescence change in a novel SCC-MOF.

A novel silver-chalcogenolate cluster-based framework Ag12TPPA·AA with long-lived afterglow was successfully synthesized. It transformed into more densely packed Ag12TPPA·AB and Ag12TPPA·ABC by layer sliding accompanied by macroscopic crystal contraction and changing luminescence.