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We found two Zn(ii) compounds with similar metalloviologen structures that, upon being exposed to light at room temperature in air, generated Zn(i) species.

The non-uniform aggregation of fast-diffused Li on an anode surface would aggravate its tip-effect-induced nucleation/growth, leading to the notorious dendrite growth in Li metal batteries (LMBs). Tuning the Li diffusion on the anode surface has been regarded previously as a mainstream method to induce its uniform deposition, while the diffusion of Li in the anode bulk is usually ignored. Here, conceptually different from the classic surface modification, we propose a molecular tunnelling strategy to construct atomic channels in graphite bulk, which enables the fast diffusion of superdense Li. Density functional theory calculations and ab initio molecular dynamics simulations prove that the bulk diffusion through atomic channels could become a new and dominating path. Its reversible and efficient diffusion has been further visualized by in situ transmission electron microscopy. As a result, when coupled with high-loading LiFePO4 cathodes (20 mg cm−2), a high areal capacity and 100% capacity retention are achieved over 370 cycles. Through this work a new strategy is developed based on the bulk-diffusion of superdense Li for dendrite-free LMBs, which can be pervasive in other high-performance energy storage systems.

A new insight into the pressure-induced transition in graphite has been presented based on the DAC technique with hydrostatic pressure by compressing the well-crystallized HOPG.

By increasing contact between pre-existing paramagnetic centers and photoinduced radicals, a photochromic single-molecule magnet with large magnetization change (+20.9%) at room temperature and paramagnetic to ferromagnetic transition was successfully achieved. The increasing amplitude of magnetization was the largest among the radical-based photomagnetic systems.

Hard carbon materials have been recognized as a promising family of anode materials for potassium ion batteries (PIBs), but their practical application is severely hindered due to the inferior initial coulombic efficiency (ICE) and low capacity. Herein, we report our findings in simultaneously improved potassium storage capacity and ICE through the design of nano-size and porous structure and the appropriate selection of electrolytes. Benefiting from the high specific surface area, stable electrode|electrolyte interface, and fast potassium ion and electron transfer, the optimized electrode exhibits a high ICE of up to 68.2% and an outstanding reversible capacity of 232.6 mA h g-1 at 200 mA g-1. In particular, superior cycling stability of 165.2 mA h g-1 at 1000 mA g-1 and 129.7 mA h g-1 at 2000 mA g-1 can be retained after 1500 cycles, respectively. Quantitative analysis reveals that this optimized structure leads to an enhanced surface-controlled contribution, resulting in fast potassiation kinetics and electronic|ionic conductivities, which are regarded as essential features for potassium storage. Our findings in this work provide an efficient strategy to significantly improve potassium storage capacity while maintaining a high ICE for hard carbon electrodes.

Photoinduced generation of stable radicals is important for photochromism, photoswitching and other applications, but was limited only to a few systems. An unprecedented series of triazole-based donor–acceptor organic molecules were found to form heat/air-stable triplet diradicals in the solid state and show a clear color change through photoinduced intramolecular charge separation, which was confirmed by electron spin resonance studies, ultrafast laser flash photolysis analyses and density functional theoretical calculations. In these molecules, electron-withdrawing substituents were more beneficial to the photoinduced charge separation than electron-donating ones. Moreover, a high molecular dipole moment was more conducive to photoinduced charge separation in the presence of an electron-withdrawing substituent.

Photoinduced electron transfer (PET) with the formation of stable radicals plays an important role in many areas. In this work, PET and color change of two sulfone-based donor–acceptor molecules were observed for the first time in the solid state. Generation of radicals was confirmed by experimental and theoretical data. The radicals could be stable in the air and at high temperature (e.g. 105 °C) in the solid state. Introducing an electron-donating substituent (such as –NH2) increases the molecular dipole moment and promotes the PET process. Sulfone-based molecules observed in this work and their analogs may be applied in several potential applications such as photoswitching, photochromism, energy conversion, and photocatalysis.

Two multiwalled carbon nanotubes (MWNTs) were seamlessly connected via the crystallization of a bridging amorphous carbon (a-C) joint using a transmission electron microscope. Technically, such a CNT connection involves electron beam induced deposition of amorphous carbon at the gap between the two nanotubes, followed by a controlled Joule heating process. Upon heating, the deposited a-C crystalized into a multi-layer tubular structure that merges into open-ended CNT shells, forming continuous graphitic layers across the junction. For the first time, seamless repairing of a pure MWNT after its electrical breakdown is thus achieved, accompanied by the nearly full recovery of its electrical conductance. More generally, we demonstrated its usage in the seamless joining of any two nanotubes, regardless of their difference in diameter, chirality, shell number and axis orientation. Molecular dynamics calculations reveal more details on how the a-C joint evolves into coherent sp2-bonded networks connecting the given nanotube pairs, thus highlighting the unique ability of the C system to reconstruct itself into any required sp2 graphitic configuration at high temperature. This seamless-joining method can be further extended to the connection between nanotubes and graphene, exhibiting its particular technological importance for building novel sp2 carbon-based nanostructures and devices via the bottom-up approach.

Viologen (N,N′-disubstituted bipyridinium) compounds are well known for their electron-transfer photochromic properties and many potential applications. However, viologen-based organic molecules, especially those with aliphatic hydrocarbon substituents, are inclined to be hygroscopic, and most of the known viologen compounds need dozens of seconds or even several minutes to exhibit photoinduced color change. The viologen–carboxylate zwitterion ligand, N,N′-dipropionate-4,4′-bipyridinium (L), is highly hygroscopic and its shortest coloration time is 5 s upon irradiation of a Xe lamp (ca. 110 mW cm−2). After coordination with ZnCl2, the obtained new compound [Zn2LCl4]n (ZnLCl) is highly stable in a wet environment (e.g. 60% relative humidity), and its shortest coloration time is 1 s upon irradiation of the same Xe lamp. X-ray diffraction analysis coupling with multiple experimental spectra (UV-vis, ESR, XPS, and IR) and density of states (DOS) calculations revealed that the photoinduced coloration of L and ZnLCl is contributed mainly by O → pyridinium and Cl → pyridinium electron transfer, respectively. The lower electronegativity of Cl over O and the shorter donor–acceptor separation may explain why ZnLCl has a shorter coloration time. Moreover, enhancement of molecular rigidity by the coordination structure may account for the improvement of moisture stability.

Changing N-substituents to modify energy gaps is important for the diverse applications (photochromism, photocatalysis, etc.) of viologen-based compounds. In situ N-substitution using alcohols under solvothermal and acidic conditions is an effective and common synthetic method for viologen-templated metal halides. In this work, we found that replacing alcohols with alkenes could reduce the reaction temperature dramatically to room temperature. A new cis/trans-viologen-templated bromoplumbate with a novel 1-D chain structure built by edge-sharing planar [Pb3Br9]3− oligomers was successfully obtained. This bromoplumbate hybrid has a narrower energy gap compared with bulk PbBr2, which has been well explained by linear optical response spectra calculations and PDOS analysis.

Nonlinear optical (NLO) switchable materials are important for photonic and optoelectronic technologies. One important issue for NLO photoswitching, the most studied physical switching approach, is how to improve the switching contrast of second harmonic generation (SHG) in crystals, because the known values are generally below 3 times. Thermoswitching, as another approach, has shown impressive high SHG-switching contrasts (4–∞ times), but the fast decay of thermally induced states demands constant heat sources to maintain specific SHG intensities. We have synthesized a photochromic and thermochromic bistable acentric compound, β-[(MQ)ZnCl3] (MQ+ = N-methyl-4,4′-bipyridinium), which represents the first crystalline compound with both photo- and heat-induced SHG-switching behavior and the first example of a thermoswitchable NLO crystal that can maintain its expected second-order NLO intensity without any heat source. The SHG-switching contrast can reach about 8 times after laser irradiation or 2 times after thermal annealing. The former value is the highest recorded for photoswitchable NLO crystals. This work also indicates that higher SHG-switching contrasts may be obtained through increasing electron-transfer efficiency, variation of permanent dipole moment, and self-absorption.

In this work, we report a new mechanoresponsive luminescent Cd(ii) coordination polymer that exhibits a sensitivity to mechanical stimulation. The luminescence colour changed gradually from weak yellowish-green to bright cyan in response to different grinding sizes, thereby showing interesting mechanochromic properties, namely a grinding-enhanced luminescence and good crystalline maintenance ability.

Long-lived charge-separated states and photoswitchable photoluminescence are important for many photochemical and photophysical applications. Recent studies have demonstrated the effectiveness of MOFs to achieve long-lived charge-separated states; however, the related studies are still rather rare owing to the limited numbers of photoresponsive MOFs. In this work, a new electron-transfer photochromic MOF compound, encapsulating photoactive viologen cations, was found to exhibit a charge-separated state with a lifetime value of more than 2 months, exceeding the reported values of the analogues. In addition, the photochromic process can afford a luminescence contrast up to 10 times between two stable states, which is higher than those of most known pyridine derivative-based photochromic compounds.

Two new isostructural coordination compounds exhibit the rare difunctional properties of both electron-transfer (ET) photochromism and ET thermochromism, which are significantly affected by halogen atoms. The thermocrystallographic studies of the same single crystal have elucidated the electron-donating nature of the halogen atoms.

Two tunable white light emitting compounds with high CRI values of 96 and 88 were obtained using an inorganic–organic hybrid strategy., Single-component white light materials may create great opportunities for novel conventional lighting applications and display systems; however, their reported color rendering index (CRI) values, one of the key parameters for lighting, are less than 90, which does not satisfy the demand of color-critical upmarket applications, such as photography, cinematography, and art galleries. In this work, two semiconductive chloroplumbate (chloride anion of lead(ii)) hybrids, obtained using a new inorganic–organic hybrid strategy, show unprecedented 3-D inorganic framework structures and white-light-emitting properties with high CRI values around 90, one of which shows the highest value to date.

Two novel manganese thioarsenates, {[Mn(2,2′-bipy)2(SCN)][Mn(2,2′-bipy)](AsVS4)}2 (1, 2,2′-bipy = 2,2′-bipyridine) and {[Mn(2,2′-bipy)2(SCN)]2[AsIII2(S2)2S2]} (2), containing thiocyanate-modified Mn-2,2′-bipy complex cations were synthesized. They feature two terminal [Mn(2,2′-bipy)2(SCN)]+ complex cations bridged by a polyanion {[Mn(2,2′-bipy)]2(AsVS4)2}2− for 1 and a cyclic thioarsenate anion (AsIII2S6)2− for 2. In 2, the [AsIII2(S2)2S2]2− anion can be described as two (AsIIIS3)3− trigonal-pyramids interlinked through S–S bonds. The method to obtain new metal complex cations shown here, introducing an anionic second ligand to modify the number of coordination sites and the charges of the metal complex cations simultaneously, is different from the traditional methods, varying either the TM center or the organic ligand or employing mixed neutral organic ligands, and may open up a new route for preparing novel chalcogenidometalates. Compounds 1 and 2 exhibit wide optical gaps of 2.20 and 2.67 eV, respectively, and photoluminescence with the emission maxima occurring around 440 nm. Magnetic measurements show the presence of antiferromagnetic interactions between MnII centers in the two compounds.

The distinct synergetic characteristics between each component in inorganic-organic hybrids offer various possibilities to obtain new "smart", high performing materials. Growing interest in this field has largely expanded the content of photochromic materials for the purpose of improving existing photochromic materials, fabricating photoresponsive devices, and exploring new families of photochromic materials. In this feature article, we give a brief review of photochromic hybrids of metal halides, metal cyanides, polyoxometalates, and metal chalcogenides as well as photochromic metal-organic complexes.

Two bifunctional 1H-tetrazolate-5-carboxylate ligands with different flexibilities, H2tza (1H-tetrazolate-5-acetic acid) and H2tzf (1H-tetrazolate-5-formic acid), were employed in the construction of zinc(II) complexes in the presence/absence of secondary ligands such as 2,2′-bipy and 4,4′-bipy. Three tza coordination polymers and two tzf dinuclear complexes, namely [Zn(tza)(H2O)]n (1), [Zn3(tza)2Cl2(2,2′-bipy)2(H2O)2]n (2), [Zn2(tza)2(4,4′-bipy)]n (3), [Zn(tzf)(H2O)3]2·2H2O (4) and [Zn(tzf)(2,2′-bipy)(H2O)]2·H2O (5), were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Polymer 1 is a 3-D two-fold interpenetrating diamond-like network with tetranuclear [Zn(COO)]4 clusters as tertiary building units (TBUs) and µ3-κN3:κO2:κO1,N1 bridging tza as linkers. Polymer 2 presents a 2-D structure formed by the linkage of 1-D Zn-carboxylate [Zn(COO)]n helical chains and µ3-κN4:κO2:κO1,N1 bridging tza. In 3, 2-D (4,4) nets are built up with dinuclear [Zn(COO)]2 clusters and µ3-κN4:κO2:κO1,N1 bridging tza, which are pillared through 4,4′-bipy to gain a 3-D self-penetrating LB-1 (446108) topology. In dinuclear complexes 4 and 5, two Zn(II) atoms are bridged by a tzf ligand in a µ2-κN2:κO1,N1 fashion. The results denote that tetrazolate-5-carboxylate ligands can adopt variable coordination modes in the formation of the complexes, and different Zn-carboxylate aggregates can serve as tertiary building units (TBUs). The effects of the nature of tetrazolate-5-carboxylate ligands and secondary ligands, and hydrothermal reaction conditions on the structural topologies of the obtained complexes have been investigated. The photoluminescent properties and thermal stabilities of 1–5 have also been discussed.

A novel inorganic–organic hybrid [Cu(2,2′-bipy)2I]2n(PbI3)2n·nDMF·nH2O (1), which exhibits diplex single-crystal-to-single-crystal transformation, can transform to a guest molecule released compound [Cu(2,2′-bipy)2I]n(PbI3)n (1a) by thermal induction, or to both a guest molecule released and ligand exchanged compound [Cu(2,2′-bipy)3]n(Pb2I6)n (1b) by solvent induction.

A series of one-dimensional (1-D) N-succinopyridine-based complexes: [Cu(L−)(H2O)2]Cl·2H2O (1), [Pr(L−)(H2O)4]Cl2 (2), [Ln(L−)(H2O)5]Cl2·3H2O (Ln = Eu (3), Gd (4)), and [Er(L−)(H2O)4]Cl2·H2O (5) (HL = N-succinopyridine (−OOC–CH(N+C5H5)–CH2–COOH)) have been prepared and characterized by single-crystal X-ray diffraction. The frameworks of complexes 1, 2 and 5 constructed from dinuclear metal building blocks exhibit 1-D double-strand loop-like chains; these chains are further connected to each other by hydrogen bonds forming a 3-D supramolecular architecture. Whereas complexes 3 and 4 feature hydrogen bonding 2-D supramolecular networks assembled from 1-D chains that are constructed from mononuclear metal building blocks. The effects of different metal ions, steric hindrance and coordination diversities of HL on the polymeric architectures have been discussed. In addition, thermogravimetric and magnetic properties of these complexes were also investigated in this paper.

A Pd/α-Al2O3 nanocatalyst with ultra-low Pd loading exhibits high activity and stability for CO oxidative coupling to dimethyl oxalate, which was prepared by a Cu(2+)-assisted in situ reduction method at room temperature. The small size and high dispersion of Pd nanoparticles facilitated by Cu(2+) ions are responsible for the excellent catalytic activity.

We investigate the impact of different derivatives of 1,4-diazabicyclo[2.2.2]octane on the crystal structures of iodoplumbates by systematically increasing the size of the same organic amine, and present two new 1-D iodoplumbates. Optical studies reveal the semiconductor characteristics of all as-synthesized iodoplumbate hybrids.

Two fluorescent cadmium complexes, [HL][CdCl2(H2O)2] (1) and [HL][CdBr2(H2O)2] (2) (HL = N-succinopyridine), have been prepared and characterized by single-crystal X-ray diffraction. Complex 1 contains a unique μ2-Cl bridged neutral 2D inorganic layer, which is further connected to isolated HL molecules by hydrogen bonds forming a hamburger-like OIO 2D supramolecular architecture. Complex 2 features a 3D supramolecular network assembly from 1D inorganic chains and discrete organic molecules through hydrogen bonds. Thermogravimetric, luminescent properties and theoretical calculations of 1 and 2 are also discussed. Moreover, UV-to-Vis tunable emissions for N-succinopyridine and 1 as well as blue-to-green tunable emission for 2 are observed.

A novel inorganic–organic hybrid (H2DAB)(Pb2I6)·2H2O, is employed as a new nitrite detection reagent with extremely high sensitivity and selectivity, in which the organic component features dual functions that afford a self-supplied acidic environment and act as a reagent for spectrophotometrically detecting nitrite anions. This new nitrite detection reagent effectively simplifies the test procedure and can be used to qualitatively distinguish nitrites with the naked eye in rural and remote areas.

The stabilization of the (SnS4)4− anion in the coordination of [Mn(phen)]2+ complexes brings about a novel compound {[Mn(phen)]2(SnS4)}n·nH2O (1), in which an unprecedented link mode of the (SnS4)4− anion is observed. Theoretical calculations indicate that TM complexes with big π-conjugated ligands, such as [Mn(phen)]2+, can serve as an excellent electron reservoir to stabilize the (SnS4)4− anion in 1, despite its strong condensation tendency. Magnetic measurements show the presence of strong antiferromagnetic interactions between the Mn2+ ions in 1.

NSF of China [20701037, 20801026]; NSF for Distinguished Young Scientist of China [20425104]; 973 program [2009CB939801]; Key Project from the CAS [KJCX2.YW.M10]; NSF of Fujian Province [2008I0026]

A ferroelectric inorganic–organic hybrid based on in situ substituted stilbazolium cation (TAMS2+ = trimethylamino-N-methyl stilbazolium) has been obtained. Single-crystal X-ray structure analysis demonstrates that the NLO-phore organic component of the complex is embedded into the inorganic polymeric [Bi2Cl8]2− framework and shows a polar arrangement with the cooperation of the nonsymmetric inorganic component. The measurement of ferroelectric and nonlinear optical properties show typical ferroelectricity and second harmonic generation (SHG) responses as well as a significant improvement of the laser damage threshold and thermal stability of relative organic material.

Using cyanide anions and sulfur simple substance as precursors of thiocyanate groups, three desired luminescent halogeno-thiocyano-d10 metal complexes, namely, [Me4N][Cu(SCN)Br] (1) with a 1-D to 2-D architecture constructed through C–H⋯Br hydrogen bonds, [Me4N][Cu(SCN)I] (2) with a 1-D to 3-D framework constructed through C–H⋯I hydrogen bonds, and [Me4N][Ag2(SCN)2Cl] (3) with a special 3-D nanoporous structure constructed by µ-chloride atoms connecting the 2-D neutral ∞2[Ag2(SCN)2] layers, have been solvothermally synthesized and all exhibit efficient luminescence. The luminescent behavior of the three complexes was illustrated through the density functional theory.

A new mixed-framework mercury selenide diselenite, (Hg(3)Se(2))(Se(2)O(5)) (1), has been prepared by a solid-state reaction and structurally characterized by single-crystal X-ray diffraction analysis. The crystal structure of 1 consists of parallel stair-like cationic (Hg(3)Se(2))(2+) chains, which are bridged by (Se(2)O(5))(2-) anionic groups to form a novel 2-D layered mixed-framework. The optical properties were investigated in terms of the diffuse reflectance and microscopic infrared spectra. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that compound 1 is a semiconductor, and that the optical absorption of 1 is mainly ascribed to the charge transitions from the O-2p and Se(-II)-4p states to the Se(IV)-4p and Hg-6s states.

Five zinc complexes of T-shaped trans-1,2,3-propenetricarboxylic acid (H(3)L) with 1-D ribbon-like chain, 2-D rhombus-grid-like and herringbone-like layers, and non-interpenetrating 3-D open framework have been obtained based on different building blocks. X-ray single crystal analyses show that the T-shaped information of H(3)L was nicely expressed in the construction of herringbone-like or ladder-like structure. All compounds were found to display blue fluorescent emissions.