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We elucidate the complex thermodynamics of sodium (Na) intercalation into the sodium super-ionic conductor (NaSICON)-type electrode, NaxV2(PO4)3, for promising Na-ion batteries with high-power density. This is the first report of a computational temperature-composition phase diagram of the NaSICON-type electrode NaxV2(PO4)3. Based on our computational data, we identify a thermodynamically stable phase with a composition of Na2V2(PO4)3 and describe its structural features. We also identify another metastable configuration that can occur at room temperature, namely Na3.5V2(PO4)3. We unveil the crystal-structure and the electronic-structure origins of the ground-state compositions associated with specific Na/vacancy arrangements, which are driven by charge orderings on the vanadium sites. These results are significant for the optimization of high-energy and power density electrodes for sustainable Na-ion batteries. [ABSTRACT FROM AUTHOR]

Na-ion batteries are promising devices for smart grids and electric vehicles due to the cost effectiveness arising from the overall abundance of sodium (Na) and its even geographical distribution. Among other factors, the energy density of Na-ion batteries is limited by the cathode electrode chemistry. NaSICON-based electrode materials are known for their wide range of electrochemical potentials, high ionic conductivity, and most importantly their structural and thermal stabilities. Using first-principles calculations, we chart the chemical space of 3d transition metal-based NaSICON phosphates with the formula NaxMM′(PO4)3 (with M and M′ = Ti, V, Cr, Mn, Fe, Co and Ni) to analyze their thermodynamic stabilities and the intercalation voltages for Na+ ions. Specifically, we compute the Na insertion voltages and related properties of 28 distinct NaSICON compositions. We investigate the thermodynamic stability of Na-intercalation in previously unreported NaxMn2(PO4)3 and NaxVCo(PO4)3. The calculated quaternary phase diagrams of the Na–P–O–Co and Na–P–O–Ni chemical systems explain the origin of the suspected instability of Ni and Co-based NaSICON compositions. From our analysis, we are also able to rationalize anomalies in previously reported experimental data in this diverse and important chemical space. [ABSTRACT FROM AUTHOR]

The complete 31P NMR chemical shift tensors for 22 inorganic phosphates obtained from ab initio computation are found to correspond closely to experimentally obtained parameters. Further improvement was found when structures determined by diffraction were geometry optimized. Besides aiding in spectral assignment, the cases where correspondence is significantly improved upon geometry optimization point to the crystal structures requiring correction. [ABSTRACT FROM AUTHOR]

In a search for Pb-free photovoltaic materials, a double perovskite Cs2AgSbBr6 with an indirect optical bandgap of 1.64 eV has been synthesized. Single crystal X-ray diffraction determined the space group as Fm3̅m with a = 11.1583(7) Å. The black, as-synthesised compound turned brown after heat treatment at 480 K while the symmetry and crystallinity were preserved. X-ray photoelectron spectroscopy indicated the existence of Sb5+ in the black crystals, suggesting that the dark colour arises from the Sb3+–Sb5+ charge transfer. Furthermore, UV visible spectroscopy and density functional theory calculations have been applied to probe the optical properties and electronic structure. [ABSTRACT FROM AUTHOR]

Trivalent metal hypophosphites with the general formula M(H2PO2)3 (M = V, Al, Ga) adopt the ReO3 structure, with each compound displaying two structural polymorphs. High-pressure synchrotron X-ray studies reveal a pressure-driven phase transition in Ga(H2PO2)3 that can be understood on the basis of ab initio thermodynamics. [ABSTRACT FROM AUTHOR]

Perovskite-derived hybrid platinum iodides with the general formula A2PtIVI6 (A = formamidinium FA and guanidinium GUA) accommodate excess I2 to yield hydrogen-bond-stabilized compounds where the I2 forms catenates with I− anions on the PtI6 octahedra. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskites and their inorganic analogues, such as MAPbI3 (MA = methylammonium, CH3NH3) and CsPbI3, are currently under intense investigation due to their high-power conversion efficiencies and low cost for solar cell applications. Herein, we investigate the effect of methylammonium and the inorganic A-cations on the elastic and related transport properties of halide perovskites using van der Waals (vdW) corrected density functional theory (DFT) calculations. For inorganic halide perovskites we find that the bonding within the inorganic framework is mainly responsible for their elastic behavior. However, our DFT calculations show that when a MA cation is substituted into the structure the combined effects of stericity (conformation) and hydrogen-framework interactions improve the material's resistance to deformation. For example, the orientationally-averaged Young's modulus of orthorhombic MAPbI3 increases by about 19% compared to the equivalent inorganic series of structures. We also find that, within the carrier-acoustic phonon scattering regime, the electron and hole carrier mobilities of hybrid halide perovskites are lowered by the hydrogen-bonding-induced tilting of the inorganic octahedra. Taken together, these results can help guide the optimization of the mechanical and transport properties of perovskite-based solar cell materials. [ABSTRACT FROM AUTHOR]

More than 20 000 MOFs have been reported to date, with different combinations of metal ions/centers and organic linkers, and they can be grown into various 3D, 2D, 1D and 0D morphologies. The flexibility in control over varying length scales from atomic scale up to bulk structure allows access to an almost endless variety of MOF-based and MOF-derived materials. Indeed, MOFs themselves have been studied as a class of useful functional materials. More remarkably, extensive research conducted in recent years has shown that MOFs are exceptionally good precursors for a large variety of nanohybrids as active materials in both electrocatalysis and energy storage. As they already contain both carbon and well-dispersed metal atoms, MOFs can be converted to conductive carbons decorated with active metal species and doping elements through appropriate pyrolysis. Due to the great diversity accessible in the composition, structure, and morphology of MOFs, several types of MOF-derived nanohybrids are now among the best performing materials both for electrocatalysts and electrodes in various energy conversion and storage devices. In addition to mesoporous nano-carbons, both doped and undoped, carbon–metal nanohybrids, and carbon-compound nanohybrids, there are several types of core@shell, encapsulated nanostructures, embedded nanosystems and heterostructures that have been developed from MOFs recently. They can be made in either free-standing forms, nano- or micro-powders, grown on appropriate conducting substrates, or assembled together with other active materials. During the MOF to active material conversion, other active species or precursors can be inserted into the MOF-derived nanostructures or assembled on surfaces, leading to uniquely new porous nanostructures. These MOF-derived active materials for electrocatalysis and energy storage are nanohybrids consisting of more than functional components that are purposely integrated together at desired length scales for much-improved performance. This article reviews the current status of these nanohybrids and concludes with a brief perspective on the future of MOF-derived functional materials. [ABSTRACT FROM AUTHOR]

Following the recent discovery of the [A]Mn(H2POO)3 (H2POO− = hypophosphite) perovskite family, we report the A = [NH2(CH3)2]+ (dimethylammonium, DMA) member. This phase shows an unusually large unit cell due to the position of the A-site cation within the perovskite cage windows rather than the centre, as is the norm. We discuss the tendency of the hypophosphite perovskite skeleton to accommodate differently shaped A-site cations through the generation of unconventional tilts and columnar shifts, then enumerate these tilts and shifts for all known [A]Mn(H2POO)3 phases. [ABSTRACT FROM AUTHOR]

The diversity of halide materials related to important solar energy systems such as CsPbX3 (X = Cl, Br, I) is explored by introducing the transition metal element Fe. In particular a new compound, Cs3Fe2Br9 (space group P63/mmc with a = 7.5427(8) and c = 18.5849(13) Å), has been synthesized and found to contain 0D face-sharing Fe2Br9 octahedral dimers. Unlike its isomorph, Cs3Bi2I9, it is black in color, has a low optical bandgap of 1.65 eV and exhibits antiferromagnetic behavior below TN = 13 K. Density functional theory calculations shed further light on these properties and also predict that the material should have anisotropic transport characteristics. [ABSTRACT FROM AUTHOR]

We investigate the variable temperature (100–450 K) and high-pressure (p = ambient − 0.74 GPa) crystal chemistry of the black perovskite formamidinium lead iodide, [(NH2)2CH]PbI3, using single crystal X-ray diffraction. In both cases we find a phase transition to a tetragonal phase. Our experimental results are combined with first principles calculations, providing information about the electronic properties of [(NH2)2CH]PbI3 as well as the most probable orientation of the [(NH2)2CH]+ cations. [ABSTRACT FROM AUTHOR]

By decoupling the mechanical behaviour of building units for the first time in a wine-rack framework containing two different strut types, we show that lithium l-tartrate exhibits NLC with a maximum value, Kmax = −21 TPa−1, and an overall NLC capacity, χNLC = 5.1%, that are comparable to the most exceptional materials to date. Furthermore, the contributions from molecular strut compression and angle opening interplay to give rise to so-called “hidden” negative linear compressibility, in which NLC is absent at ambient pressure, switched on at 2 GPa and sustained up to the limit of our experiment, 5.5 GPa. Analysis of the changes in crystal structure using variable-pressure synchrotron X-ray diffraction reveals new chemical and geometrical design rules to assist the discovery of other materials with exciting hidden anomalous mechanical properties. [ABSTRACT FROM AUTHOR]

We have used a family of Zr-based metal–organic frameworks (MOFs) with different functionalized (bromo, nitro and amino) and extended linkers for drug delivery. We loaded the materials with the fluorescent model molecule calcein and the anticancer drug α-cyano-4-hydroxycinnamic acid (α-CHC), and consequently performed a mechanical amorphization process to attempt to control the delivery of guest molecules. Our analysis revealed that the loading values of both molecules were higher for the MOFs containing unfunctionalized linkers. Confocal microscopy showed that all the materials were able to penetrate into cells, and the therapeutic effect of α-CHC on HeLa cells was enhanced when loaded (20 wt%) into the MOF with the longest linker. On one hand, calcein release required up to 3 days from the crystalline form for all the materials. On the other hand, the amorphous counterparts containing the bromo and nitro functional groups released only a fraction of the total loaded amount, and in the case of the amino-MOF a slow and progressive release was successfully achieved for 15 days. In the case of the materials loaded with α-CHC, no difference was observed between the crystalline and amorphous form of the materials. These results highlight the necessity of a balance between the pore size of the materials and the size of the guest molecules to accomplish a successful and efficient sustained release using this mechanical ball-milling process. Additionally, the endocytic pathway used by cells to internalize these MOFs may lead to diverse final cellular locations and consequently, different therapeutic effects. Understanding these cellular mechanisms will drive the design of more effective MOFs for drug delivery applications. [ABSTRACT FROM AUTHOR]

We report the synthesis of a 2D-layered metal–organic framework incorporating weakly interacting chains designed to aid exfoliation of the layers into nanosheets. Dispersion of the nanosheets exposes labile metal-sites which are shown to exchange solvent molecules allowing the nanosheets to act as sensors in suspension. [ABSTRACT FROM AUTHOR]

Density functional theory screening of the hybrid double perovskites (MA)2BIBiX6 (BI = K, Cu, Ag, Tl; X = Cl, Br, I) shows that systems with band gaps similar to those of the MAPbX3 lead compounds can be expected for BI = Cu, Ag, Tl. Motivated by these findings, (MA)2TlBiBr6, isoelectronic with MAPbBr3, was synthesised and found to have a band gap of ∼2.0 eV. [ABSTRACT FROM AUTHOR]

Three highly crystalline Cu(ii)-polyoxometalate (POM) complexes, [Cu1.5(H2O)7.5PW12O40]·4.75H2O and cis- and trans-[Cu2(H2O)10SiW12O40]·6H2O, were successfully synthesized and characterized by single crystal and powder X-ray diffraction as well as thermogravimetric analysis. All complexes feature octahedrally coordinated, Jahn–Teller-distorted CuII centres, which are coordinated by one terminal oxygen atom of the POM anion and five water molecules. The crystal structure of [Cu1.5(H2O)7.5PW12O40]·4.75H2O, reveals four-fold disorder at one of the two Cu-sites, whereas [Cu2(H2O)10SiW12O40]·6H2O crystallizes in two fully-ordered polymorphic forms: a monoclinic structure containing an angled cis configuration of the Cu-POM-Cu molecule and a triclinic structure containing a linear trans configuration. Density functional theory (DFT) calculations show that the cis polymorph of [Cu2(H2O)10SiW12O40]·6H2O is more stable than the trans form by about 30 kJ mol−1. [ABSTRACT FROM AUTHOR]

Among the panoply of exciting properties that metal–organic frameworks (MOFs) exhibit, fully reversible pressure-induced phase transformations (PIPTs) are particularly interesting as they intrinsically relate to the flexibility of MOFs. Recently, a number of MOFs have been reported to exhibit this feature, which is attributed to bond rearrangement with applied pressure. However, the experimental assessment of whether a given MOF exhibits PIPT or not requires sophisticated instruments as well as detailed structural investigations. Can we capture such low pressure transformations through simulations is the question we seek to answer in this paper. For this, we have performed first-principles calculations based on the density functional theory, on a MOF, [tmenH2][Y(HCOO)4]2 (tmenH22+ = N,N,N′,N′-tetramethylethylenediammonium). The estimated lattice constants for both the parent and product phases of the PIPT agree well with the earlier experimental results available for the same MOF with erbium. Importantly, the results confirm the observed PIPT, and thus provide theoretical corroborative evidence for the experimental findings. Our calculations offer insights into the energetics involved and reveal that the less dense phase is energetically more stable than the denser phase. From detailed analyses of the two phases, we correlate the changes in bonding and electronic structure across the PIPT with elastic and electronic conduction behavior that can be verified experimentally, to develop a deeper understanding of the PIPT in MOFs. [ABSTRACT FROM AUTHOR]

Eleven novel coordination compounds, composed of chrysazin (1,8-dihydroxyanthraquinone) and different first-row transition metals (Fe, Co, Ni, Cu), were synthesised and the structures determined by single-crystal X-ray diffraction. The synthetic trends were investigated using high-throughput synthesis under systematic variation of concentration and reagent stoichiometry: for complexes containing Co, Ni or Cu crystallisation was improved by low ligand : metal ratios, while the effect of concentration depended on the metal used. The compounds crystallise as discrete clusters, apart from two, which contain long Cu–O bonds which may allow the two compounds to be considered one-dimensional coordination polymers. One of these compounds shows a distance between aryl rings of less than 3.26 Å, which is shorter than that in graphite, suggesting applications as an organic–inorganic semiconductor. The compound was found to be insulating by single-crystal and powder AC-impedance measurements, and this result is discussed with reference to the electronic structure calculated using density-functional theory. [ABSTRACT FROM AUTHOR]

It will be very interesting for many important reactions to endow highly active catalysts with momentum-transfer efficiency. However, the intrinsic magnetism of ferromagnetic catalysts is difficult to exploit due to the interaction between the catalyst and stirring devices. Herein, a catalytically active and super paramagnetic Co–carbon–rGO composite (CCGC) was synthesized and used as a nanoactuator to simultaneously achieve momentum-transfer and hydrolysis of NaBH4 or H3NBH3 for hydrogen production. The CCGC magnetically transferred momentum in a batch or continuous flow reactor. The external magnetic field can drive the catalyst to transfer momentum for excellent agitation. The catalyst can be fixed at an appointed position in the continuous flow for efficient separation. The separation of the catalyst from the reaction mixture also becomes facile. The CCGC showed superior retention as a pollutant adsorbent for the removal of Rhodamine B (Rh-B) from water in the absence of magnetic or mechanical stirring apparatus. The unique momentum-transfer properties, as well as excellent catalysis and adsorption, warrant its promising application in the corresponding fields. [ABSTRACT FROM AUTHOR]

The wide-ranging properties of metal organic frameworks (MOFs) rely in many cases on the presence of defects within their structures and the disorder that is inevitably associated with such defects. In the present work we review several aspects of defects in MOFs, ranging from simple substitutional defects at metal cation or ligand positions, to correlated defects on a larger length scale and the extreme case of disorder associated with amorphous MOFs. We consider both porous and dense MOFs, and focus particularly on the way in which defects and disorder can be used to tune physical properties such as gas adsorption, catalysis, photoluminescence, and electronic and mechanical properties. [ABSTRACT FROM AUTHOR]

Flexible metal–organic frameworks (MOFs) can undergo fascinating structural transitions triggered by external stimuli, such as adsorption/desorption of specific guest molecules or temperature changes. In this detailed study we investigate the potentials and limitations of tuning framework flexibility systematically by exploiting the powerful concept of mixed-linker solid solutions. We chose the prototypical family of functionalized pillared-layer MOFs of the general type Zn2(fu1-bdc)2x(fu2-bdc)2−2xdabco (with x = 1.00, 0.75, 0.50, 0.25 and 0.00; fu-bdc = 2,5-dialkoxy-1,4-benzenedicarboxylate with varying alkoxy chain length, dabco = 1,4-diazabicyclo[2.2.2]octane) and examined their guest responsive, as well as intrinsic temperature dependent structural flexibility by X-ray diffraction, gas physisorption and calorimetric measurements. The ratio of the different fu-bdc linkers can be adjusted freely, offering opportunity for a targeted design of these functional materials by modulating their key features, such as magnitude of framework contraction upon guest removal, breathing behaviour upon CO2 adsorption/desorption, thermoresponsive phase behaviour, and their general thermal expansivity, by the careful choice of fu-bdc linkers and their combination. [ABSTRACT FROM AUTHOR]

X-ray diffraction has been used to investigate the kinetics of amorphization through ball-milling at 20 Hz, for five zeolitic imidazolate frameworks (ZIFs) – ZIF-8, ZIF-4, ZIF-zni, BIF-1-Li and CdIF-1. We find that the rates of amorphization for the zinc-containing ZIFs increase with increasing solvent accessible volume (SAV) in the sequence ZIF-8 ＞ ZIF-4 ＞ ZIF-zni. The Li–B analogue of the dense ZIF-zni amorphizes more slowly than the corresponding zinc phase, with the behaviour showing a correlation with their relative bulk moduli and SAVs. The cadmium analogue of ZIF-8 (CdIF-1) amorphizes more rapidly than the zinc counterpart, which we ascribe primarily to its relatively weak M–N bonds as well as the higher SAV. The results for the ZIFs are compared to three classical zeolites – Na-X, Na-Y and ZSM-5 – with these taking up to four times longer to amorphize. The presence of adsorbed solvent in the pores is found to render both ZIF and zeolite frameworks more resistant to amorphization. X-ray total scattering measurements show that amorphous ZIF-zni is structurally indistinguishable from amorphous ZIF-4 with both structures retaining the same short-range order that is present in their crystalline precursors. By contrast, both X-ray total scattering measurements and 113Cd NMR measurements point to changes in the local environment of amorphous CdIF-1 compared with its crystalline CdIF-1 precursor. [ABSTRACT FROM AUTHOR]

The understanding of lithium–oxygen coordination systems is important for making better lithium conductors as well as active materials for lithium ion batteries. Here, we report a systematic investigation on coordination environments in lithium coordination polymers (LCPs) through the syntheses and analyses of six new crystals composed of lithium ions and anthraquinone (aq) derivative anions, where the negative charges are distributed in π-conjugation systems. Their structures were determined by single-crystal X-ray diffraction to be (1) [Li2(23dcaq)(H2O)] in space group P21/c, (2) [Li(23dcaqH)] in P21/c, (3) [Li2(15dhaq)(H2O)2] in P21/c, (4) [Li2(14dhaq)(H2O)2] in Pnma, (5) [Li(14dhaqH)(H2O)] in P212121 and (6) [Li(14hnaq)(H2O)] in P212121 (23dcaq2− = 2,3-dicarboxy-aq, 14dhaq2− = 1,4-dihydroxy-aq, 15dhaq2− = 1,5-dihydroxy-aq and 14hnaq− = 1-hydroxy-4-nitro-aq). Through the comprehensive structure analysis of these materials as well as other LCPs, we found that when considering the longest C–O bond in the π-conjugation system of an anionic organic molecule and its coordination to a Li ion, there is a weak inverse relationship between the C–O and Li–O bond lengths. In addition, despite exhibiting optical band edges below 2 eV and 1D π-stacking connectivity, conductivity measurements on single crystals of 1–6 confirmed that they are all electronic insulators. We rationalize this finding on the basis of π-orbital delocalization, which is more restricted in the aq-based LCPs compared to known semiconducting hybrid materials. [ABSTRACT FROM AUTHOR]

Microporous polymers with molecular sieving properties are promising for a wide range of applications in gas storage, molecular separations, catalysis, and energy storage. In this study, we report highly permeable and selective molecular sieves fabricated from crosslinked polymers of intrinsic microporosity (PIMs) incorporated with highly dispersed nanoscale fillers, including nonporous inorganic nanoparticles and microporous metal–organic framework (MOF) nanocrystals. We demonstrate that the combination of covalent crosslinking of microporous polymers via controlled thermal oxidation and tunable incorporation of nanofillers results in high-performance membranes with substantially enhanced permeability and molecular sieving selectivity, as demonstrated in separation of gas molecules, for example, air separation (O2/N2), CO2 separation from natural gas (CH4) or flue gas (CO2/N2), and H2 separation from N2 and CH4. After ageing over two years, these nanofiller-tuned molecular sieves became more selective and less permeable but maintained permeability levels that are still two orders of magnitude higher than conventional gas separation membranes. [ABSTRACT FROM AUTHOR]

Polymorphism in formate-based dense metal–organic frameworks with the general formula ABX3 is predicted by quantum chemical calculations and confirmed experimentally. In particular [NH3NH2]Zn(HCOO)3 crystallizes in two different polymorphs, a perovskite-like framework and a chiral structure with hexagonal channels. A detailed thermodynamic analysis reveals that both structures are very close in free energy and that entropy driven effects are responsible for stabilizing the channel structure. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate frameworks (ZIFs) have attracted great interest in recent years due to their high chemical and thermal stability with promising applications in gas storage and separations. We investigate the structures of three different crystalline ZIFs – ZIF-4, ZIF-8, ZIF-zni – and their amorphous counterparts using high field 13C and 15N CP MAS NMR. The high field (20 T) allows for the observation of all crystallographically independent carbon and nitrogen atoms in the crystalline ZIFs. Combining our experimental results with density functional theory calculations enabled the assignment of all chemical shifts. The crystalline spectra reveal the potential of high field NMR to distinguish between two ZIF polymorphs, ZIF-4 and ZIF-zni, with identical [Zn(C3H3N2)2] chemical compositions. 13C and 15N CP MAS NMR data obtained for the amorphous ZIFs clearly showed signal broadening upon amorphization, confirming the retention of chemical composition and the structural similarity of amorphous ZIF-4 and ZIF-zni. In the case of amorphous ZIF-8, we present evidence for the partial de-coordination of the 2-methyl imidazole linker. [ABSTRACT FROM AUTHOR]

We report an experimental study of the mechanical properties of the organic–inorganic halide perovskites, CH3NH3PbX3 (X = I, Br and Cl). Nanoidentation on single crystals was used to obtain Young's moduli (E) and hardnesses (H) of this class of hybrid materials, which have attracted considerable attention for photovoltaic applications. The measured Young's moduli of this family lie in the range 10–20 GPa and a trend of ECl ＞ EBr ＞ EI is observed. The physical properties are consistent with the underlying crystal structure. In particular, the results are in reasonable agreement with recent calculations using density functional theory and align with expectations based upon bond energy, packing, and hydrogen-bonding considerations. The anisotropy in these systems is quite small, with E100 ＞ E110 for the cubic bromide and chloride cases and E112≈E100 for the tetragonal iodide perovskites. Interestingly, CH3NH3PbI3 is harder than the Br- and Cl-based perovskites. [ABSTRACT FROM AUTHOR]

We report the encapsulation of the hydrophilic model molecule calcein in the Zr-based MOF UiO-66, followed by amorphization of the framework by ball-milling. We show controlled release of calcein over more than 30 days, compared with the 2 day release period from crystalline UiO-66. [ABSTRACT FROM AUTHOR]

The deep red phosphor Sr4(PO4)2O:Eu2+, which has an excitation peak around 450 nm for blue LED applications, is reported. This behavior is unusual for most phosphate phosphors. The crystal structure of Sr4(PO4)2O:Eu2+ is found to be monoclinic P21 and isotypic with Ca4(PO4)2O:Eu2+, which also shows deep red emission. Sr4(PO4)2O:Eu2+ has a larger lattice volume than Ca4(PO4)2O:Eu2+, but their emission and excitation spectra at room temperature are very similar. The key factors are discussed for achieving a large redshift of the 5d levels of Eu2+ ion in order to emit red light. In particular, the importance of the anion polarizability and the distortions of the metal coordination polyhedra are discussed, including the effective coordination number. Importantly, Sr4(PO4)2O:Eu2+ lacks the yellow emission at 77 K, which is found in Ca4(PO4)2O:Eu2+. The differences in thermal quenching behavior for Eu2+ dopants in Sr4(PO4)2O:Eu2+ and Ca4(PO4)2O:Eu2+ are attributed to the degree of auto/photo-ionization due to differences in the band gaps of these compounds. The importance of the large band gap of the host lattice in avoiding non-radiative processes of energy relaxation was confirmed. [ABSTRACT FROM AUTHOR]

First principles calculations on the hybrid perovskite CH3NH3PbI3 predict strong hydrogen-bonding which influences the structure and dynamics of the methylammonium cation and reveal its interaction with the tilting of the PbI6 octahedra. The calculated atomic coordinates are in excellent agreement with neutron diffraction results. [ABSTRACT FROM AUTHOR]

Elastic properties and acoustic dissipation associated with the disorder-order ferroelectric transition in a single crystal metal-organic framework (MOF), ijNH4][Zn(HCOO)3], have been investigated using resonant ultrasound spectroscopy IJRUS) in the temperature range between 10 K and 300 K. The paraelectric to ferroelectric transition at around 192 K is triggered by the disorder-order transition of ammonium cations within the structure and changes of hydrogen bonding, accompanied by a structural phase transition from the non-polar hexagonal space group P6322 to the polar hexagonal space group P63. The elastic moduli, which are proportional to the square of resonant frequencies, gradually decrease with increasing temperature, and the rate of decrease changes markedly near the transition temperature. The acoustic dissipation tends to gradually increase with increasing temperature, but with a peak near the transition point. This pattern of behaviour can be understood by analogy with phase transitions driven by hydrogen bonding coupled to lattice strain in the mineral lawsonite ijCaAl2Si2O7(OH)2·H2O]. The newly formed hydrogen bonds act as braces to stiffen the structure, as opposed to the elastic softening which typically occurs at displacive phase transitions. The acoustic loss mechanism involves dynamical disordering of hydrogen atoms between symmetry related positions and coupling of their motion with local lattice strain. [ABSTRACT FROM AUTHOR]

A new blue-green phosphor, Ca6BaP4O17:Ce3+, which can be prepared by conventional solid-state synthesis, is reported as a candidate phosphor for solid-state lighting with near-ultraviolet LEDs. Under excitation at around 400 nm, Ca6BaP4O17:Ce3+ shows strong blue-green emission with the peak position at 477 nm. Ce3+,Si4+ co-doping is found to enhance the luminous intensity, and the unique emission characteristics of this combination are studied and related to the crystal structure. Ca6BaP4O17 is an exceptional host material, which also accommodates Eu2+, emitting strong yellow light under 400 nm excitation. A fabricated white LED, combining Ca6BaP4O17:Ce3+,Si4+ with Ca6BaP4O17:Eu2+ and a red CaAlSiN3:Eu2+ phosphor, achieved a luminous efficacy of 45 lm W-1 with a color-rendering index of 93 around the correlated color temperature of 4500 K. [ABSTRACT FROM AUTHOR]

Upon heating, lithium L-malate undergoes topotactic dehydration to form a phase containing the unsaturated fumarate ligand, in which the original 3-D framework remains intact. Insight into this unusual transformation has been obtained by single crystal X-ray diffraction, MAS-NMR, in situ powder X-ray diffraction and DFT calculations. [ABSTRACT FROM AUTHOR]

A new phase, Ca6BaP4O17, was found in the CaO–BaO–P2O5 phase diagram and its Eu2+-doped derivative was evaluated as a possible phosphor for solid-state lighting. Ca6BaP4O17 was prepared by conventional solid-state synthesis and its structure was solved ab initio from high-resolution, synchrotron X-ray powder diffraction data. The bandgap of Ca6BaP4O17 was estimated to be 5.79 eV. Under excitation with UV to blue light, Ca6BaP4O17:Eu2+ shows strong yellow emission with the peak position at 553 nm. A white LED, which was fabricated with an InGaN blue chip and Ca6BaP4O17:Eu2+, achieved a luminous efficacy of 31 lm W−1 with a color-rendering index of 78 around the correlated color temperature of 6500 K. [ABSTRACT FROM AUTHOR]

We report the phase behaviour of chiral, racemic and meso-lithium tartrate frameworks, which was examined as a function of solvent system, temperature and ligand isomer. Through our comprehensive investigation of this system of 14 diverse phases, we have gained detailed insight into the effect of synthesis conditions on product structure, and elucidated the thermodynamic and kinetic factors involved in phase selection. Reactions in ethanol between lithium acetate and chiral, racemic and meso-tartaric acids give rise to anhydrous kinetic products; polymorphs with higher entropy tend to appear at high temperatures. Reactions at room temperature in water-ethanol mixtures give rise to hydrated kinetic products, including two new crystal structures, [Li2(D,L-tartrate)(H2O)2]n in P̄1 and [Li2(meso-tartrate)(H2O)0.5]n in C2221, whose structures are contrasted with known anhydrous products. Reactions at elevated temperatures in water-ethanol mixtures result in the formation of low enthalpy, anhydrous products and, furthermore, the global minimum energy structure appears at high temperatures in all cases owing to in situ ligand isomerization. [ABSTRACT FROM AUTHOR]

Six novel crystalline coordination polymers composed of alkali metal ions and trithiocyanurate anions (C3N3S3H2− = ttcH2−) were synthesized. Single crystals were used both for structure determinations by X-ray diffraction and ionic conductivity measurements by AC impedance methods. The structures are: (i) sodium trithiocyanurate trihydrate, Na(ttcH2)(H2O)3 in space group P21; (ii) potassium trithiocyanurate hydrate, K(ttcH2)(H2O) in P1̅; (iii) rubidium trithiocyanurate hydrate, Rb(ttcH2)(H2O) in P1̅; (iv) rubidium trithiocyanurate hydrate, Rb3(ttcH2)2(ttcH3)2(H2O)5(OH) in P1̅; and (v, vi) two anhydrous polymorphs of caesium trithiocyanurates, Cs(ttcH2) in P1̅ and Cc. With the exception of the sodium phase, which is layered, all of these compounds consist of three dimensional coordination networks. In all systems, the inorganic regions are interleaved by arrays of ttcH2− anions. The most interesting feature of this system is the thiol-rich environment formed between the trithiocyanurate layers, where alkali metal ions are located. Water molecules, where present, are always coordinated to a cation. Among these crystals, K(ttcH2)(H2O) exhibited proton conductivity under atmospheric conditions (25 ± 0.2 °C): 1.1 × 10−5 S cm−1 in the direction perpendicular to the bc plane and 3.1 × 10−6 S cm−1 along the c axis. [ABSTRACT FROM AUTHOR]

The effect of cation valency on the complex structures of divalent and trivalent transition metal gallates has been examined using a combination of neutron and synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and XANES spectroscopy. In the divalent frameworks, M(C7H4O5)·2H2O (M = Mn, Co and Ni), it was found that charge balance was achieved viathe presence of protons on the meta-hydroxyl groups. It was also established that these compounds undergo a discontinuous phase transition at lower temperatures, which is driven by the position of the extra-framework water molecules in these materials. By contrast, in the trivalent Fe gallate, Fe(C7H3O5)·2H2O, it was found that the stronger bonding between the meta-hydroxy oxygen and the cations leads to a weakening of the bond between this oxygen and its proton. This is turn is thought to lead to stronger hydrogen bonding with the extra-framework water. The lattice water is disordered in the Fe(iii) case, which prevents the phase transition found in the M(ii) gallates. Refinement against the neutron diffraction patterns also revealed that the relatively mild microwave synthesis of gallate frameworks in D2O led to an extensive deuteration of the ortho-hydrogen sites on the aromatic ring, which may suggest a more versatile method of deuterating aromatic organics. The antiferromagnetic structure of Co gallate has also been determined. [ABSTRACT FROM AUTHOR]