Distortion Of Framework Research Articles

Color-Tuning and Near-Sunlight White Emission in Highly Stable Rod-Spacer MOFs with Defective Dicubane Based Lead(II)-Carboxyl Chains.

The active lone pair electron effect and highly flexible coordination geometry of Pb2+ prevented the rational construction of metal-organic frameworks (MOFs) but promoted excellent fluorescence tuning. The regulation on organic and alkali templates facilitated the assemblies of three new Pb-MOFs: [Pb2(pia)2(DMA)]·DMA (1), [Pb2(pia)2(DMF)]·1.5DMF (2), and [Pb2(pia)2(DMF)]·NEt3 (3). They were rigid rod-spacer and double-walls frameworks, which possess defective dicubane [Pb4O6] based metal-carboxyl chains constructed from both semidirected and holodirected Pb2+ ions. These MOFs exhibited thermal stability up to 370 °C and unprecedented chemical stability in H2O and acidic (pH 2) and alkaline (pH 12) aqueous solutions, found for the first time in Pb-MOFs. A single-phase and rare-earth-free white-emitting phosphor, 1, was screen out, which showed a near-sunlight and human-vision-friendly broadband spectrum covering the full visible region, possessing the close-to-pure-white chromaticity coordinates of (0.332, 0.347), a near-daylight color temperature of 5696 K, and a high color rendering index of 95. The replacement of DMF as apical ligand and guest in 2 resulted in an intrinsic single and narrow emission at 562 nm with yellow color. The convenient yellow-and-blue color-tuning until white for 2 was realized by either solution or solid blending with blue-emissive H2pia, benefited from their highly matched excitation spectra. Using large NEt3 as template guest induced great framework distortion for 3 and led to white emission with chromaticity coordinates of (0.302, 0.294), stemming from nonequivalent dual emission at 450 and 545 nm. In-depth structure analysis revealed intra-/interchain Pb···Pb interactions in the lead(II)-carboxyl chains greatly affected the photochemical output.

Mechanism-Property Correlation in Coordination Polymer Crystals toward Design of a Superior Sorbent.

A methodology was developed to design superior sorbents of oxoanions. To integrate the high efficiency of chemisorption, selectivity, and recyclability into one sorbent, understanding the nature of oxoanions-sorbent interactions and the structural evolution of the sorbents is essential. Three cationic Ag(I) coordination polymers (CPs) are synthesized for dichromate (Cr2O72-) removal, and three distinct oxoanion-exchange mechanisms are identified, namely, the replacement, breath, and reconstruction processes, depending on the degree of framework distortion induced by the dichromate-CP interactions. The single crystal to single crystal transformation during the oxoanion exchange has been investigated by using single-crystal X-ray diffraction and energy-dispersive X-ray microanalysis. The replacement process, due to a weak chemisorption, shows excellent recyclability at the cost of reduction of efficiency and selectivity of adsorption. The reconstruction process may achieve a high efficiency and selectivity, but it loses recyclability. Due to the formation of a Ag-O(dichromate) bond and the breathing effect of the framework, the sorbent with the breath mechanism shows both superior efficiency and high recyclability in dichromate removal. The study of perrhenate (ReO4-) removal using the same CPs demonstrates that one CP performing the reconstruction process during dichromate removal turns to the breath process in removal of perrhenate anions. These results of mechanism-property correlation provide an insight into improvement of the methodology to fabricate a superior CP sorbent for oxoanion removal.

Impact of the Copper-Induced Local Framework Deformation on the Mechanism of Structural Phase Transition in [(CH3)2NH2][Zn(HCOO)3] Hybrid Metal–Formate Perovskite

Dimethylammonium zinc formate [(CH3)2NH2][Zn(HCOO)3] (DMAZn) treated as a model dense metal–organic framework is a compound that has been intensively studied in the last decade. It undergoes a first-order order–disorder structural phase transition at T0 ∼ 167K, considered as the improper ferroelectric one. The complex mechanism of this phase transition is attributed to the ordering of the hydrogen bonds between (CH3)2NH2+ (DMA+) and the formate groups as well as distortion of the zinc–formate framework. Here, the analysis of the impact of zinc substitution by Cu doping on the order–disorder phase transition is presented. The Jahn–Teller effect of Cu2+ ions results in a local framework distortion, which consequently perturbs the structural dynamics. Based on the dielectric, thermal, structural, electron paramagnetic resonance, and IR spectroscopy measurements, it is shown that doping with Cu2+ ions leads to a decrease of the phase transition entropy and temperature as well as a change in the nature of the ...

Anomalous Temperature-Dependent Charge Recombination in CH3NH3PbI3 Perovskite: Key Roles of Charge Localization and Thermal Effect.

Optimizing metal halide perovskite solar cells necessitates understanding of nonradiative electron-hole recombination because it comprises a dominant route for charge and energy losses. In principle, the electron-hole recombination rate increases as temperature grows due to enhanced electron-phonon coupling. Experiments defy this expectation in MAPbI3 (MA = CH3NH3+). By performing nonadiabatic (NA) molecular dynamics analyses combined with time-domain density functional theory simulations, we demonstrate that nonradiative electron-hole recombination in MAPbI3 at high temperature occurs more slowly than that at low temperature. First and most important, increasing temperature enhances thermal disorder and leads to significant distortion of the inorganic Pb-I framework, giving rise to electron and hole wave functions locating spatial separation and reducing NA coupling by a factor of 28% in comparison with low temperature. Second, rising temperature enhances the thermal fluctuations of both the inorganic and organic components that accelerate decoherence process by a factor of 12%. Both factors, particularly the small NA coupling, contribute to suppressing electron-hole recombination at high temperature. The simulations show excellent agreement with experiments and emphasize how the charge localization driven by thermal effects impacts electron-hole recombination in perovskites and advances our understanding of the unusual charge dynamics.

Thermosalient Amphidynamic Molecular Machines: Motion at the Molecular and Macroscopic Scales

Summary The supramolecular amphidynamic rotor 1, composed of two carbazole molecules acting as the stator and a DABCO rotator, exhibits remarkable thermosalience above 316 K. During this process, the crystals spontaneously transduce collective molecular displacements into macroscopic movement due to a phase transition, which is described by single-crystal X-ray analyses from 100 K to 320 K. The fast rotation in the low-temperature phase (I) occurs with a low activation energy Ea(I) ≈ 2.6 kcal mol−1 and a pre-exponential factor A(I) ≈ 1012 s−1. Increased symmetry of the cavity in the high-temperature phase (II) resulted in slower dynamics, regardless of a smaller rotational barrier, Ea(II) ≈ 0.5 kcal mol−1, due to the large reduction in the pre-exponential factor to A(II) ≈ 107 s−1. These results demonstrate that a relatively small distortion of lattice framework leads to drastic dynamic effects at both molecular and macroscopic scales, helping us to understand responsive crystalline materials.

Efficient and Stable CsPbI3 Solar Cells via Regulating Lattice Distortion with Surface Organic Terminal Groups.

All-inorganic cesium lead iodide perovskites (CsPbI3 ) are promising wide-bandgap materials for use in the perovskite/silicon tandem solar cells, but they easily undergo a phase transition from a cubic black phase to an orthorhombic yellow phase under ambient conditions. It is shown that this phase transition is triggered by moisture that causes distortion of the corner-sharing octahedral framework ([PbI6 ]4- ). Here, a novel strategy to suppress the octahedral tilting of [PbI6 ]4- units in cubic CsPbI3 by systematically controlling the steric hindrance of surface organic terminal groups is provided. This steric hindrance effectively prevents the lattice distortion and thus increases the energy barrier for phase transition. This mechanism is verified by X-ray diffraction measurements and density functional theory calculations. Meanwhile, the formation of an organic capping layer can also passivate the surface electronic trap states of perovskite absorber. These modifications contribute to a stable power conversion efficiency (PCE) of 13.2% for the inverted planar perovskite solar cells (PSCs), which is the highest efficiency achieved by the inverted-structure inorganic PSCs. More importantly, the optimized devices retained 85% of their initial PCE after aging under ambient conditions for 30 days.

Computational Prediction and Experimental Verification of ε-Caprolactone Ring-Opening Polymerization Activity by an Aluminum Complex of an Indolide/Schiff-Base Ligand

Computational screening of a series of aluminum complexes for their activity in the ring-opening transesterification polymerization (ROTEP) of e-caprolactone (CL) was performed using a “framework distortion energy” (FDE) hypothesis. An {N,N,N,N}-aluminum complex with a bis-indolide Schiff-base ligand was predicted on the basis of that screening to be an efficient catalyst, and this prediction was tested and verified experimentally through the synthesis and characterization of the complex and evaluation of its ROTEP reactivity.

Mechanistic insights into structural and surface variations in Y-type zeolites upon interaction with binders

Zeolite Y is one of the most important solid acid catalysts that find immense applications in catalytic processes such as fluid catalytic cracking (FCC), acylation and cumene cracking. The technical grades of FCC catalyst require specifications that are met by dispersing the zeolite in amorphous binders. On contact with binders, zeolite properties in composite catalysts alter. This article reports an insight into structural and surface modifications of Y zeolites caused by binders’ incorporation. Experiments employing various characterization techniques, including solid state MAS-NMR and FTIR reveal alumina incorporation adjusts zeolite framework in comparison with silica binder. Incorporation of alumina binder into zeolite Y polarizes the framework by extra-framework alumina species (such as Al3+, AlO+ and Al(OH)2+) coming from the binder. The polarization, apparent with USY and REY, is considered as the operating mechanism for distortion of zeolite framework, involving the attraction of aluminum species from the binder to the framework of zeolite and its subsequent framework structure reorientation. Compensating framework Na+ cations restrain the polarization of NaY framework due to its deficiency of protons, revealing Brönsted acid sites as active centers for the zeolite framework polarization. The resulting alumina bound catalysts are amorphized by layers of alumina materials that implicate the Brönsted acidity as a function of its weight in the catalyst. Catalytic reaction reveals that polarization of the zeolite framework by extra-framework alumina species decreases the transformation of paraffin to carbenium ion, increasing the hydrogen transfer reaction pathway.

The quest for optimal water quantity in the synthesis of metal-organic framework MOF-5

Abstract Efficient and simple room temperature synthesis of pure phase metal-organic framework MOF-5 has been developed, based on the use of anhydrous zinc acetate, Zn(OAc)2, as a precursor, instead of zinc acetate dihydrate. Crucial influence of water on a reaction pathway was revealed. In order to obtain MOF-5, different amounts of water have been added into the solutions of Zn(OAc)2 in N,N-dimethylformamide (DMF) to prepare in situ zinc acetate hydrates with 0.25, 0.5, and 1.0 mol of water. Commercially available zinc acetate dihydrate was also used as a precursor for comparison. These solutions were mixed at room temperature with the solution of 1,4-benzenedicarboxylic acid in DMF in the absence of any base. Based on XRD, FTIR, and SEM measurements, it was shown that the optimal amount of water for the synthesis of completely pure, crystalline phase MOF-5 is 0.25–0.5 mol of water per one mole of Zn. The reaction systems with 1.0 and 2.0 mol of water per one mole of Zn also led to solids with MOF-5 as the dominant phase, but they also contain small amounts of another phase, formed due to the decomposition (hydrolysis) and/or distortion of the MOF-5 framework in the presence of excess amounts of water. The product synthesized in the system without any added water contains MOF-5 phase in a very small amount, while main phase is zinc 1,4-benzenedicarboxylate and/or zinc hydrogen 1,4-benzenedicarboxylate. Regular cubic submicro/microcrystal morphology exhibited the samples synthesized using 0.5 and 0.25 mol water per one mole of Zn (pure MOF-5), while for the samples synthesized at mole ratios H2O/Zn2+ = 1.0 and 2.0 other particle shapes are also seen. By nitrogen sorption measurements it was found that the highest values of BET specific surface area (1937 m2 g−1), micropore volume (0.83 cm3 g−1), and micropore area (1590 m2 g−1) showed MOF-5 prepared at mole ratio H2O/Zn2+ = 0.5, while the highest yield of MOF-5 is obtained with the theoretical mole ratio H2O/Zn2+ = 0.25. Thermal stability of synthesized materials was investigated by TGA.

Modulated Structures in PbHfO<sub>3</sub> Crystals at High-Pressure-High-Temperature Conditions

Lead hafnate single crystals were characterized using single crystal x-ray diffraction under simultaneous application of hydrostatic pressure and high temperatures. The information on the structure of two intermediate phases, situated between antiferroelectric and paraelectric phases in the pressure-temperature phase diagram, has been obtained. The lower-temperature intermediate phase is characterized by incommensurate displacive modulations in Pb sublattice. The higher-temperature intermediate phase is characterized by oxygen framework distortion, primarily in the form of anti-phase tilts of the oxygen octahedra, which is also present in the lower-temperature intermediate phase.

Effects of Charge, Size, and Shape of Transition States, Bound Intermediates, and Confining Voids in Reactions of Alkenes on Solid Acids

AbstractSolid acids with sites varying in acid strength and in confining environments are used here to examine, through kinetic experiments and theory, how size and shape of organic guests and inorganic hosts at ion‐pair transition states (TS) influence reactivity. Reactions of C2−C4 alkene mixtures serve as the illustrative example; they involve kinetically‐relevant C−C coupling between alkenes and bound alkoxides that saturate the surface on microporous (TON) and mesoporous (SiAl) aluminosilicates of similar acid strength and on stronger heteropolytungstic acids (HPW). Rate constants (per H+) increase with increasing TS size (number of C‐atoms) because of the combined effects of size/substitution on proton affinities of coupling products and on van der Waals (vdW) contacts between carbocations and voids. When the voids and organic moieties are similar in dimension, these contacts require framework distortions, leading to dispersive interactions that are compensated in part by enthalpic penalties associated with the distortions, which are quantified here with DFT‐derived atomic displacements and distortion energies. DFT‐derived proton affinities of the coupling products and vdW interaction energies between the TS and voids represent the most accurate and complete descriptors of reactivity, as the size and shape of TS structures vary in C−C coupling steps and more generally in acid‐catalyzed transformations, and can be used in designing voids for stabilizing specific host‐guest pairs.

A Metal–Organic Framework with Cooperative Phosphines That Permit Post‐Synthetic Installation of Open Metal Sites

AbstractPCM‐101 is a phosphine coordination material comprised of tris(p‐carboxylato)triphenylphosphine and secondary pillaring groups coordinated to [M3(OH)]5+ nodes (M=Co, Ni). PCM‐101 has a unique topology in which R3P: sites are arranged directly trans to one another, with a P⋅⋅⋅P separation distance dictated by the pillars. Post‐synthetic coordination of soft metals to the P: sites proceeds at room temperature to provide X‐ray quality crystals that permit full structural resolution. Addition of AuCl groups forces a large distortion of the parent framework. In contrast, CuBr undergoes insertion directly between the trans‐P sites to form dimers that mimic solution‐phase complexes, but that are geometrically strained due to steric pressure exerted by the MOF scaffold. The metalated materials are active in heterogeneous hydroaddition catalysis under mild conditions, yielding different major products compared to their molecular counterparts.

A Metal-Organic Framework with Cooperative Phosphines That Permit Post-Synthetic Installation of Open Metal Sites.

PCM-101 is a phosphine coordination material comprised of tris(p-carboxylato)triphenylphosphine and secondary pillaring groups coordinated to [M3 (OH)]5+ nodes (M=Co, Ni). PCM-101 has a unique topology in which R3 P: sites are arranged directly trans to one another, with a P⋅⋅⋅P separation distance dictated by the pillars. Post-synthetic coordination of soft metals to the P: sites proceeds at room temperature to provide X-ray quality crystals that permit full structural resolution. Addition of AuCl groups forces a large distortion of the parent framework. In contrast, CuBr undergoes insertion directly between the trans-P sites to form dimers that mimic solution-phase complexes, but that are geometrically strained due to steric pressure exerted by the MOF scaffold. The metalated materials are active in heterogeneous hydroaddition catalysis under mild conditions, yielding different major products compared to their molecular counterparts.

Pressure-Induced Structural Evolution and Optical Properties of Metal-Halide Perovskite CsPbCl3

Metal-halide perovskites have emerged as the most promising semiconductor materials for advanced photovoltaic and optoelectronic applications. Herein, we comprehensively investigate the optical response and structural evolution of metal-halide perovskite CsPbCl3 (ABX3) upon compression. Band gap realized a pronounced narrowing under mild pressure followed by a sharp increase, which could be ascribed to Pb–Cl bond contraction and inorganic framework distortion, respectively. The transformation of the crystal structure is confirmed and analyzed through in situ high-pressure X-ray diffraction and Raman experiments, consistent with the evolution of optical properties. Combining with the first-principles calculations, we understand the electronic band structure changes and phase transition mechanism, which are ascribed to severe PbCl6 octahedral titling and twisting. Our results demonstrate that the high-pressure technique can be used as a practical tool to modify the optical properties of metal-halide perovsk...

A Review of Mechanoluminescence in Inorganic Solids: Compounds, Mechanisms, Models and Applications.

Mechanoluminescence (ML) is the non-thermal emission of light as a response to mechanical stimuli on a solid material. While this phenomenon has been observed for a long time when breaking certain materials, it is now being extensively explored, especially since the discovery of non-destructive ML upon elastic deformation. A great number of materials have already been identified as mechanoluminescent, but novel ones with colour tunability and improved sensitivity are still urgently needed. The physical origin of the phenomenon, which mainly involves the release of trapped carriers at defects with the help of stress, still remains unclear. This in turn hinders a deeper research, either theoretically or application oriented. In this review paper, we have tabulated the known ML compounds according to their structure prototypes based on the connectivity of anion polyhedra, highlighting structural features, such as framework distortion, layered structure, elastic anisotropy and microstructures, which are very relevant to the ML process. We then review the various proposed mechanisms and corresponding mathematical models. We comment on their contribution to a clearer understanding of the ML phenomenon and on the derived guidelines for improving properties of ML phosphors. Proven and potential applications of ML in various fields, such as stress field sensing, light sources, and sensing electric (magnetic) fields, are summarized. Finally, we point out the challenges and future directions in this active and emerging field of luminescence research.

Sterically Induced Ligand Framework Distortion Effects on Catalytic Cyclic Ester Polymerizations.

Aluminum alkoxide complexes supported by salen ligands [salen = N, N'-bis(salicylaldimine)-2-methylpropane-1,2-diamine or N, N'-bis(salicylaldimine)-2,2-dimethylpropane-1,3-diamine] with o-adamantyl substituents have been synthesized and investigated for the polymerization of ε-caprolactone. Geometric analysis of the catalysts used for the reaction reveals the metal coordination geometries to be intermediate between square-pyramidal and trigonal-bipyramidal. A detailed kinetic study accompanied by density functional theory modeling of key mechanistic steps of the reaction suggest that, in addition to the length of the backbone linker, the o-aryl substituents have a significant impact on the catalyst's reactivity. Bulky ortho substituents favorably distort the precatalyst geometry and thereby foster the achievement of the rate-limiting transition-state geometry at low energetic cost, thus accelerating the reaction.

Metal-loaded pollucite-like aluminophosphates: dissymmetrisation of crystal structures and physical properties

Two aluminophosphate analogues of the mineral pollucite with the general formula Cs2(M,Al)3P3O12 (where M = Cu or Mn) have been synthesized by high-temperature flux and structurally characterized using the single-crystal X-ray diffraction. Both samples crystallize in cubic I4132 space group, Z = 8, with a = 13.5911(5) and a = 13.8544(7) for Cu- and Mn-loaded phases, respectively. Their framework structures are based on the ANA-type topology and exhibit the partial ordering of the metal (M/Al) and phosphorus (P) cations over the tetrahedral sites. The regular changes in cell dimensions and volumes in the row Cs2(Cu,Al)3P3O12→Cs2(Mn,Al)3P3O12 obviously correspond to increasing radii of the transition metal. The crystal chemical analysis of both pollucite-like phases show correlations between the difference in the radii size of tetrahedral cations and the degree of distortion of flexible ANA-type framework due to decreasing of the intertetrahedral angles (T–O–T). Magnetic susceptibility measurements indicate that both compounds are paramagnets in the temperature range of 2–300 K.

Mitigating Cation Diffusion Limitations and Intercalation-Induced Framework Transitions in a 1D Tunnel-Structured Polymorph of V2O5

The design of cathodes for intercalation batteries requires consideration of both atomistic and electronic structure to facilitate redox at specific transition metal sites along with the concomitant diffusion of cations and electrons. Cation intercalation often brings about energy dissipative phase transformations that give rise to substantial intercalation gradients as well as multiscale phase and strain inhomogeneities. The layered α-V2O5 phase is considered to be a classical intercalation host but is plagued by sluggish diffusion kinetics and a series of intercalation-induced phase transitions that require considerable lattice distortion. Here, we demonstrate that a 1D tunnel-structured ζ-phase polymorph of V2O5 provides a stark study in contrast and can reversibly accommodate Li-ions without a large distortion of the structural framework and with substantial mitigation of polaronic confinement. Entirely homogeneous lithiation is evidenced across multiple cathode particles (in contrast to α-V2O5 partic...

Raman‐scattering studies of pressure‐induced phase transitions in perovskite‐like acetamidninium manganese formate

AbstractWe report high‐pressure Raman scattering studies of acetamidninium manganese formate, which show evidence for two pressure‐induced phase transitions between 0.7 and 1.4 GPa and above 5.3 GPa. The first transition is related to distortion of the manganese formate framework whereas the second one affects significantly the structure of the acetamidinium cation. Significant narrowing of the lattice bands suggests that the intermediate and high‐pressure phases are ordered. High‐pressure experiments also indicate different structures of the intermediate phases observed upon compression and decompression. However, release of pressure to ambient value leads to recovery of the initial ambient‐pressure phase.

Fabrication of stable glycine/palygorskite nanohybrid via high-pressure homogenization as high-efficient adsorbent for Cs(I) and methyl violet

Abstract A series of stable glycine/palygorskite (GLY/PAL) nanohybrid absorbents were prepared by incorporating GLY molecules into PAL via a simple high-pressure homogenization. The structural characterization demonstrated that 3.15% of GLY molecules were incorporated into the GLY/PAL hybrid adsorbent and formed H-bonding interactions with siloxane and inner channels of PAL, which caused slight distortion of the crystalline framework. Compared with conventional surface modification, high-pressure homogenization and heat treatment enabled GLY to insert into PAL channels well to form hybrid nanostructure. Among all hybrid absorbents, the 60GLY/PAL showed the highest adsorption capacities of 147 mg/g for methyl violet (MV) and 80 mg/g for Cs(I) as well as the removal ratios of 98% for MV and 80% for Cs(I) from 150 mg/L of MV and 100 mg/L of Cs(I) solutions, respectively. In contrast, raw PAL (without modification) could adsorb only 112 mg/g of MV and 45 mg/g of Cs(I). This work has demonstrated that utilizing a simple high-pressure homogenization process improved stability of GLY/PAL nanohybrid absorbents by increasing the incorporation of guest (GLY) molecules into the tunnels/channels of hosts (PAL), leading to a novel enhanced adsorbent for Cs(I) and MV. This finding has provided a new way to fabricate nanohybrid adsorbents.