Crystal and Band-Gap Engineering of One-Dimensional Antimony/Bismuth-Based Organic-Inorganic Hybrids.

Hybrid halide perovskites are emerging semiconducting materials with a diverse set of remarkable optoelectronic properties. Besides the widely studied lead halide perovskites, Pb-free metal halides such as Bi- and Sb-containing hybrid organic-inorganic materials have shown potential as semiconductors and have been deemed candidates for optoelectronic devices. Here, we report a series of 1D Sb/Bi-based organic-inorganic hybrid alloys: [4ApyH]SbxBi1-xIyBr4-y, where 4ApyH stands for the 4-aminopyridine cations. These compounds are assembled by edge-sharing octahedral [MX6] units stabilizing 1D chains with organic cations filled in between. The crystallographic data of eight selected complexes show that [4ApyH]SbxBi1-xIyBr4-y has at least five phases (space group) with the difference metal and halogen content: Pbca ([4ApyH]BiI4), Pca21 ([4ApyH]Sb0.5Bi0.5I4), P21/c ([4ApyH]SbI4 (100 K), [4ApyH]BiI2Br2, [4ApyH]BiBr4, and [4ApyH]SbBr4 (100 K)), I2/a ([4ApyH]Sb0.5Bi0.5I2Br2and [4ApyH]SbI2Br2), and C2/c ([4ApyH]SbI4 (298 K) and [4ApyH]SbBr4 (298 K)). Powder X-ray diffraction shows that the phase of the sample changes with a change of the metal and halogen ratios, and the change law accords with Vegard's law. The optical band gaps are heavily affected by the metal and halide contents, ranging from 1.94 eV for [4ApyH]BiI4 to 2.73 eV for [4ApyH]SbBr4. When Sb substitutes for Bi to form an alloy, the band gap increases from 1.94 for [4ApyH]BiI4 to 1.67 eV for [4ApyH]SbI4, from 2.13 eV for [4ApyH]BiI2Br2 to 2.41 eV for [4ApyH]SbI2Br2, and from 2.55 eV for [4ApyH]BiBr4 to 2.73 eV for [4ApyH]SbBr4. The conductivity of [4ApyH]SbxBi1-xI4 increased from ∼1.00 × 10-15 to 2.14 × 10-8 S cm-1 with an increase of the Sb content. Solution-deposited thin films of the nine complexes show the same (110) orientation, displaying a parallel growth orientation with respect to the substrate. The devices of [4ApyH]Sb0.8Bi0.2I4 and [4ApyH]SbI4 demonstrated stable open-circuit photovoltages of 0.55 and 0.44 V, steady-state short-circuit photocurrent densities of 1.52 and 1.81 mA cm-2, and light-to-electrical energy conversion efficiencies of 0.29% and 0.30%, respectively.

Tracking the dimensional conversion process of semiconducting lead bromide perovskites by mass spectroscopy, powder X-ray diffraction, microcalorimetry and crystallography.

The structural information of a material in both the solid state and solution state is essential to the in-depth understanding of the properties of inorganic-organic hybrid materials. A one-dimensional (1D) lead bromide formulated as [H][NH3(CH2)2SS(CH2)2NH3][H2O][PbBr5] (1) could be converted into a new two-dimensional (2D) complex, [NH3(CH2)2SS(CH2)2NH3][PbBr4] (2), by soaking the crystals in water. The isolated 2D compound showed single-layer lead-halide perovskite structures. Electrospray ionization mass spectrometry (ESI-MS) analyses of the reaction solution revealed that the [PbBr3]- fragments are initially formed from the rapid decomposition of the 1D [PbBr5]3- chains and subsequently reassemble into 2D [PbBr4]2- layers, which was verified by powder X-ray diffraction (PXRD) and microcalorimetry. Because of the decomposition and reassembly process, complex 1 could be used as a precursor to synthesize M2+-doped 2D lead bromide perovskites, namely, Mn@2, Ni@2 and Cd@2. In addition, preliminary tests indicated that complex 2 exhibited a lower optical band gap (3.25 eV) and higher electrical conductivity (3.2 × 10-11 S cm-1) than complex 1 (3.38 eV, 5.4 × 10-12 S cm-1).

Monodisperse Bismuth-Halide Double Perovskite Nanocrystals Confined in Mesoporous Silica Templates.

Metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of the properties of lead halide perovskite nanocrystals has been studied, the properties of lead-free perovskite nanocrystals are less well-understood because synthesizing them is still very challenging. Here, a simple and popularizable method has been demonstrated to grow monodisperse bismuth-halide double perovskite nanocrystals, Cs2AgBiBr6 (1), inside three kinds of mesoporous silica templates. The size and morphology of nanocrystals depend on the structure and pore size of the template. Structural analysis shows that the nanocrystals of various sizes and morphologies retain the crystal structure of bimetallic perovskite. 1 exhibits different morphologies in the silicon channels of three templates: square nanoparticles in KIT-6, spherical and rodlike particles in SBA-15, and nanowires in MCM-41. UV-vis-NIR and photoluminescence measurements show us the variation of band gap and carrier recombination time due to quantum confinement of nanocrystals in mesoporous silicon materials. The band gaps of nanocrystals in the template exhibit an obvious blue shift compared with that of the bulk sample, and the carrier recombination time is significantly shortened. We show that mesoporous silicon templates can be used to prepare lead-free perovskite nanocrystals, and the controllable preparation of nanocrystals can be achieved by the template's own characteristics. This provides a new idea for us to find new functional materials of lead-free metal halide solid-state light-emitting diodes.

Two-Dimensional Silver(I)-Dithiocarboxylate Coordination Polymer Exhibiting Strong Near-Infrared Photothermal Effect.

Materials that demonstrate near-infrared (NIR) absorption and can simultaneously convert the electromagnetic irradiation into heat are promising for photothermal therapy. Traditionally, such a material is either pure inorganic, such as CuS, Ag2S, and carbon nanotube, or pure organic, such as polyaniline, polypyrrole, and conjugated polymers. Here we show that strong NIR photothermal effect can also be achieved in inorganic-organic hybrid coordination polymers (CPs) or metal-organic frameworks (MOFs). Our strategy is to construct CPs with inorganic Ag-S components that are interlinked by the organic ligands into a higher-dimensional hybrid network. Interestingly, the two resulting CPs, [Ag(Py-4-CSS)] n 1 and [Ag2(Py-4-CSS)(Py-4-CSSS)] n 2 (Py-4-CSS = pyridine-4-dithiocarboxylate; Py-4-CSSS = pyridine-4-perthiocarboxylate), show disparate structures due to the varied coordination mode of the pyridine group. For 1, the N atom coordinates to the Ag+ center and forms a two-dimensional square framework, while for 2, such a Ag-N bond is disconnected and forms only a one-dimensional structure. Interestingly, this difference leads to the distinct absorption properties in the NIR region. Under 800 nm radiation, the temperature of 1 can rise up to 24.5 °C in 3 min with photothermal conversion efficiency of 22.1%, which is about 2× that of pure inorganic Ag2S material and among the highest compared to various known inorganic materials, for example, Au nanoshells (13%), nanorods (21%), and Cu2- xSe nanocrystals (22%) irradiated with 800 nm light, while for 2, the NIR absorption is absent. This result first demonstrates that the inorganic-organic hybrid approach can be applied to construct superior NIR photothermal materials, but the control of the structure is vital. Here the coordinating nitrogen atoms in 1 are conceived to be critical in promoting the charge transfer between the dithiocarboxylate ligands. To elucidate the response to NIR irradiation of 1, we measured the heat capacity and dielectric constant of 1 and also performed density functional theory calculations. Significantly, the large dielectric constant and flat energy bands indicates 1 is much easier to be polarized and has a high electron effective mass. Thus, unlike the pure inorganic material, such as Ag2S, in which electron and hole can quantum mechanically combine to give off light, the joint-force of organic ligands in 1 effectively enhances polaronic recombination into heat.

Syntheses, crystal-solution structures and magnetic properties of a series of decanuclear heterometallic [LnCoCo] (Ln = Eu, Gd, Tb, Dy) clusters.

Four unprecedented decanuclear heterometallic [Ln2CoII4CoIII4] clusters based on a diethanolamine ligand (H2dea), namely [Eu2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·4CH3OH·2H2O (1), [Gd2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·4CH3OH·2H2O (2), [Tb2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·2CH3OH·4H2O (3) and [Dy2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·2CH3OH·4H2O (4) were synthesized through a facile solution method. Single-crystal X-ray diffraction analyses reveal that complexes 1-4 consist of a [Ln2CoII4CoIII4] core, which is constructed by bridging a quasi-double cuboidal [Ln2CoII2CoIII2] core with two [CoIICoIII] units. Electrospray ionization mass spectrometry (ESI-MS) using methanol solution reveals that complexes 1-4 are stable in the solution, and the clusters undergo three different substitution reactions (Cl- replaced by OH-, OH- replaced by CH3O- and HCOO- replaced by OH-/CH3O-) at the same time in the ionization state. Magnetic susceptibilities reveal ferromagnetic couplings within complexes 3 and 4, and the magnetocaloric effect (MCE) for 2 was also evaluated and the maximum entropy change (-ΔSm) value reaches 16.3 J kg-1 K-1 at about 3 K and 5 T.

Redox-Active Cobalt(II/III) Metal-Organic Framework for Selective Oxidation of Cyclohexene.

We report herein a new cobalt(II/III) mixed-valence metal-organic framework formulated as [CoIICo2III(µ3-O)(bdc)3(tpt)]·guest 1, where bdc = benzene-1,4-dicarboxylate and tpt = 2,4,6-tri(4-pyridinyl)-1,3,5-triazine, which can be used as a redox-active heterogeneous catalyst for selective oxidation of cyclohexene on the allylic position without destroying the adjacent double bond. Two oxidants were chosen to demonstrate this result. For using tert-butyl hydroperoxide, the conversion rate is 63% and only allylic oxidation products ( tert-butyl-2-cyclohexenyl-1-peroxide, 86%; 2-cyclohexen-1-one, 14%) are found, whereas if using O2 as oxidant, a total conversion of 38% is achieved and also only the allylic oxidation products (cyclohexenyl hydroperoxide, 72%; 2-cyclohexen-1-one, 20%; and cyclohex-2-en-1-ol, 8%) are found. The absence of any adduct on the double bond may be due to the unique radical chain mechanism triggered by the mixed-valent [CoIICo2III(µ3-O)] centers.

Cobalt(II) Magnetic Metal-Organic Framework with an Effective Kagomé Lattice, Large Surface Area, and High Spin-Canted Ordering Temperature.

To make a porous material with high magnetic ordering temperature is challenging because the low density of the material is adverse to the dense magnetic moment, a prerequisite to high-performance magnets. Herein, we report a hollow magnetic metal-organic framework (MMOF) [Co3(bpdc)3(tpt)0.66] 1 (H2bpdc = 4,4'-biphenyldicarboxylic acid) with a Langmuir surface area of 1118 m2/g and spin-canted long-range magnetic ordering up to 22 K. Such a high performance is owing to the unique antiferromagnetic Kagomé lattice made of ferromagnetic Co3 clusters and conjugated 2,4,6-tri(4-pyridinyl)-1,3,5-triazine (tpt) ligands, which is closely coupled with each other via double-interpenetration of the porous networks. Moreover, a parameter defined as the product of magnetic ordering/blocking temperature and the surface area for measuring the performance of porous molecular magnets is proposed.

Direct Observation of Confined I- ⋠⋠⋠I2 ⋠⋠⋠I- Interactions in a Metal-Organic Framework: Iodine Capture and Sensing.

Herein a strategy is reported for capturing and sensing iodine by strong I- ⋅⋅⋅I2 ⋅⋅⋅I- interaction, confined in a metal-organic framework, [Tb(Cu4 I4 )(ina)3 (DMF)] (1) (ina=isonicotinate). As revealed by single-crystal X-ray crystallography, the uptaken I2 molecules directly contact the {Cu4 I4 }n chains, virtually forming an electronically polarizable tetraiodide anion (I42- ) through strong I- ⋅⋅⋅I2 ⋅⋅⋅I- interaction. As such, a quasi-copper-iodide layer of {Cu4 I5 }n with semiconducting characteristics results, leading to a significant enhancement (Δσ =107 times) in electrical conductivity over the I2 -free 1. The effect observed is several orders of magnitude higher than those reported due to iodine⋅⋅⋅aromatic interactions (Δσ =102 times) and by interactions between I2 and a redox-active metal centre (Δσ =104 times). The drastic enhancement in electrical conductivity was used to switch on/off an LED bulb, suggesting the possibility of electrically sensing I2 .

Assembly of a Highly Stable Luminescent Zn5 Cluster and Application to Bio-Imaging.

The assembly sequence of the coordination cluster [Zn5 (H2 L(n) )6 ](NO3 )4 ]⋅8 H2 O⋅2 CH3 OH (Zn5 , H3 L(n) =(1,2-bis(benzo[d]imidazol-2-yl)-ethenol) involves in situ dehydration of 1,2-bis(benzo[d]imidazol-2-yl)-1,2-ethanediol (H4 L) through the formation of the [Zn(H3 L)2 ](+) monomer, dimerization to [Zn2 (H3 L)2 ](+) , dehydration of the ligand to [Zn2 (H2 L(n) )2 ](+) , and the final formation of the pentanuclear cluster. The cluster has the following special characteristics: 1) high stability in both refluxing 37 % HCl and 27 % NH3 , 2) low cytotoxicity, and 3) pH-sensitive fluorescence in the visible-to-near-infrared (Vis/NIR) region in the solid state and in solution. We have applied it as a fluorescent probe both in vivo and in vitro. Its H-bonding ability is the key to its affinity and selectivity for imaging lysosomes in HeLa cells and tumors in male BALB/C mice. It provides a new type of sensitive and biocompatible fluorescent probe for detecting small tumors (13.5 mm(3) ).

Construction of magnet-type coordination polymers using high-spin {Ni4}-citrate cubane as secondary building units.

Three potassium(i)-nickel(ii)-citrate coordination polymers, [K4Ni6(cit)4(H2O)8]n (), [K14Ni17(cit)12(H2O)33]n·10nH2O () and [K8Ni12(cit)8(H2O)15]n·2nH2O (), have been self-assembled in a solvothermal synthesis. Interestingly, these three polymers share the common {Ni4(cit)4}(8-) cubane ({Ni4}-cit-cub) secondary building units. The diverse ways of linking the {Ni4}-cit-cubs and additional isolated octahedral Ni(ii) ions lead to disparate magnetic exchange-coupling interactions, namely ferromagnetic for and and antiferromagnetic for . More importantly, the weak ferromagnetic interactions do not lead to long-range magnetic ordering above 2 K in or , whereas the strong antiferromagnetic interaction in leads to uncompensated magnetic moment due to the non-collinear alignment of the spins. Further magnetic characterization confirms the coexistence of spin-canted antiferromagnetism and spin glass behaviour in .

Tracking the formation of a polynuclear Co16 complex and its elimination and substitution reactions by mass spectroscopy and crystallography.

We present the syntheses and structures of the biggest chiral cobalt coordination cluster, [Co16(L)4(H3L)8(N3)6](NO3)2·16H2O·2CH3OH (1, where H4L = S,S-1,2-bis(1H-benzimidazol-2-yl)-1,2-ethanediol). 1 consists of two Co4O4 cubes (Co4(L)2(H3L)2) alternating with Co2(EO-N3)2Co2 (Co4(L)2(H3L)2(N3)2), bridged by the benzimidazole and azide nitrogen atoms to form a twisted ring. The ligand adopts both cis and trans forms, and all the rings have the same chiralilty. ESI-MS of 1 from a methanol solution of crystals reveals the fragment [Co16(L)4(H3L)8(N3)6+2H](4+), suggesting the polynuclear core is stable in solution. ESI-MS measurements from the reaction solution found smaller fragments, [Co4(H3L)4-H](3+), [Co4(H3L)4-2H](2+), [Co4(H3L)4(N3)2](2+), and [Co2(H3L)2](2+), and ESI-MS from a methanol solution of the solid deposit found in addition the Co16 core. These results and the dependence on the synthesis time allow us to propose the process for the formation of 1, which opens up a new way for the direct observation of the ligand-controlled assembly of clusters. In addition, the isolation of [Co4(H3L)4](NO3)4·4H2O (2) consisting of separate Co4O4 cubes with the ligands being only cis in crystalline form supports the proposal. Interestingly, N3(-) is replaced by either CH3O(-) or OH(-), and this is the first time that high-resolution ESI-MS is successfully utilized to examine both the step-by-step elimination and substitution of inner bridging ligands in such a high nuclear complex. Increasing the voltage results in stepwise elimination of azide from the parent cluster. The preliminary magnetic susceptibility of 1 indicates ferromagnetic cubes antiferromagnetically coupled to the squares within the cluster, though in a field of 2.5 kOe, weak and slow relaxation is observed below 4 K.