(C₃N₆H₇)₂SbF₅·H₂O Exhibiting Strong Optical Anisotropy from the Optimal Arrangement of π‑Conjugated (C₃N₆H₇)⁺ Groups

An antimony fluoride melamine birefringent crystal, (C3N6H7)2SbF5·H2O, was obtained by introducing the π-conjugated delocalized melamine and antimony trifluoride via a simple aqueous solution evaporation method. It features one-dimensional parallel [C3N6H7]∞ chains further connected by hydrogen bonds originated from [SbF5]2– groups with lone pairs. The experimental optical band gap (4.74 eV) allows it to be used in the ultraviolet region. The first-principles calculations suggest that (C3N6H7)2SbF5·H2O exhibits a large birefringence (∼0.38@550 nm), which is twice larger than that of the commercial CaCO3 crystal. Therefore, introducing the fluoride into π-conjugated melamine may be a good tactic to obtain birefringent crystals with large optical anisotropy

Shear-Thickening in Mixed Suspensions of Silica Colloid and Oppositely Charged Polyethyleneimine

The liquid–gel–liquid transition tuned by increasing concentration of linear and hyperbranched polyethyleneimine in suspension of silica colloids, and the accompanying shear-thickening phenomena, were investigated by rheological measurements. The influence from linear and hyperbranched polymer conformation and from different size-ratio between particle and polymer on the rheological properties of suspensions flocculated by absorbing polyelectrolyte were considered. Charge neutralization and bridging mechanism are the main reasons for the flocculation of silica colloid in this study. Because of charge reversal, the irreversible bridges are turned into flexible reversible bridges with increasing adsorption amount of oppositely charged polymer, which leads to an abrupt transition from gel to liquid. Over a narrow composition range, around the gel to liquid transition region, shear-thickening flow is observed. It is found that, for given particle volume fraction, the composition region exhibiting shear-thickening for mixed suspension with linear polyethyleneimine is broader than that for mixed suspension with hyperbranched polyethyleneimine, and the onset of shear-thickening depends only on size-ratio, regardless of the actual size of particle and polymer in the range of this study. The relationship between the gel to liquid transition and shear-thickening was discussed

Three Highly Fluorescent Iridium(III) Unit Based Coordination Polymers: Coordinated Solvent-Dependent Photoluminescence

Three highly luminescent coordination polymers were solvothermally synthesized in three different solvents, i.e., H₂O, DMF (DMF = <i>N</i>,<i>N</i>-dimethylformamide), and DEF (DEF = <i>N</i>,<i>N</i>-diethylformamide) based on a superiorly luminescent Ir­(III) unit (L, L = Ir­(ppy)₂(Hdcbpy)⁻, ppy = 2-phenylpyridine, dcbpy = 2,2′-bipyridine-4,4′-dicarboxylate). The three CPs, [MgL₂(H₂O)₂]­·3.5H₂O [<b>1</b>], [MgL₂(DMF)₂]­·3.5H₂O [<b>2</b>], and [MgL₂(DEF)­(H₂O)]­·3H₂O [<b>3</b>], exhibit intense emissions, long fluorescence lifetimes, and high quantum yields. In particular, compound <b>2</b> shows a very long fluorescence lifetime up to 11.3 μs and high quantum yield up to 18.1%. Attractively, it was found that the luminescence of <b>1</b>–<b>3</b> varied from yellow to orange under the irradiation of UV light. The distinct luminescence of <b>1</b>–<b>3</b> probably is due to different coordinated solvents in the three compounds

Plastic Transition to Switch Nonlinear Optical Properties Showing the Record High Contrast in a Single-Component Molecular Crystal

To switch bulk nonlinear optical (NLO) effects represents an exciting new branch of NLO material science, whereas it remains a great challenge to achieve high contrast for “on/off” of quadratic NLO effects in crystalline materials. Here, we report the supereminent NLO-switching behaviors of a single-component plastic crystal, 2-(hydroxymethyl)-2-nitro-1,3-propanediol (<b>1</b>), which shows a record high contrast of at least ∼150, exceeding all the known crystalline switches. Such a breakthrough is clearly elucidated from the slowing down of highly isotropic molecular motions during plastic-to-rigid transition. The deep understanding of its intrinsic plasticity and superior NLO property allows the construction of a feasible switching mechanism. As a unique class of substances with short-range disorder embedded in long-range ordered crystalline lattice, plastic crystals enable response to external stimuli and fulfill specific photoelectric functions, which open a newly conceptual avenue for the designing of new functional materials

Construction of Interpenetrated Ruthenium Metal–Organic Frameworks as Stable Photocatalysts for CO₂ Reduction

Poor stability has long been a major obstacle to the practical applications of metal–organic framework (MOF) photocatalysts. This problem can be overcome by the use of structural interpenetration. In this work, by modifying Ru metalloligands, we have rationally designed two Ru–polypyridine based MOFs (with non-interpenetrated and interpenetrated structures, respectively), both of which exhibit similar photocatalytic activities for CO₂ photoreduction. Remarkably, the interpenetrated Ru-MOF possesses good photocatalytic durability and recyclability, and shows much higher thermal and photic stability in comparison with its non-interpenetrated counterpart. To the best of our knowledge, this is the first time that the stability of MOF photocatalysts was improved by using structural interpenetration

A Highly Symmetric Metal–Organic Framework Based on a Propeller-Like Ru-Organic Metalloligand for Photocatalysis and Explosives Detection

Ru­(H₂dcbpy)₃²⁺, one of the Ru­(bpy)₃²⁺ (dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid, bpy = 2,2′-bipyridine) derivatves, has been used as a propeller-like photoactive metalloligand to coordinate with indium­(III) ions to form a highly symmetric metal–organic framework [InRu­(dcbpy)₃]­[(CH₃)₂NH₂]·6H₂O (<b>1</b>), and the cubic microcrystals of <b>1</b> have been acquired through modified procedures. Compound <b>1</b> manifests broad visible light absorption band and strong red light emission with long decay lifetime, both of which are originated from the metal-to-ligand charge transfer of the Ru­(dcbpy)₃^4– metalloligands. Because of the highly light-harvesting and strong redox nature of the Ru­(dcbpy)₃²⁺ units in <b>1</b>, its photocatalysis activities were determined by visible light-induced photodegradation of methyl orange experiments. The results indicate that <b>1</b> can be a stable and good visible-light driving heterogeneous photocatalyst. Meanwhile, the sensing properties of <b>1</b> were also evaluated, and the result shows that <b>1</b> can selectively detect the nitro explosives molecules

Dynamic Entangled Framework Based on an Iridium–Organic Unit Showing Reversible Luminescence Turn-On Sensing

A new entangled metal–organic framework shows reversible structural dynamics and luminescence changing in response to the loss of guest H₂O molecules. Furthermore, an intense and sensitive luminescence turn-on sensing was observed by the naked eye for <b>1</b> upon detection of the volatile organic solvent molecule CH₃CN, accompanied by reversible structural transformation

Solvent-Dependent Formation of Cd(II) Coordination Polymers Based on a <i>C</i>₂-Symmetric Tricarboxylate Linker

Three novel solvent-dependent Cd­(II) coordination architectures [Cd₃(BPT)₂(DMF)₂]·2H₂O [<b>1</b>], [Cd₃(BPT)₂(DMA)₂] [<b>2</b>], and [(CH₃CH₂)₂NH₂]·[Cd­(BPT)]·2H₂O [<b>3</b>] were obtained by the hydrothermal reaction of a <i>C</i>₂-symmetric tricarboxylate linker, biphenyl-3,4′,5-tricarboxylic acid (H₃BPT), with cadmium nitrate in the mixed solvents of water with <i>N</i>,<i>N</i>-dimethylformamide (DMF), <i>N</i>,<i>N</i>-dimethylacetamide (DMA), diethylformamide (DEF), respectively. Single-crystal X-ray diffraction analyses reveal that complex <b>1</b> is a three-dimensional (3D) network containing infinite Cd–O–Cd chains with the solvent DMF molecule bridging the neighboring Cd1 and Cd2 centers. Though complex <b>2</b> also has a 3D network containing infinite metal-carboxylate chains, the solvent DMA molecule only coordinates to one of the Cd­(II) centers as a terminated solvent molecule. Complex <b>3</b> possesses a two-dimensional (2D) (6, 3) honeycomb type net formed by the mononuclear metal ion and the BPT ligand, which are further stacked in ABAB fashion through π–π interactions into a 3D supramolecular architecture. The effect of solvents on the formation of the coordination networks has been shown in the three compounds obtained, and the distinction of coordination architectures is due to the coordination abilities of solvent molecules with the metal centers. The structure stabilities and photoluminescent properties of the three coordination polymers have also been investigated

Solvent-Dependent Formation of Cd(II) Coordination Polymers Based on a <i>C</i>₂-Symmetric Tricarboxylate Linker

Three novel solvent-dependent Cd­(II) coordination architectures [Cd₃(BPT)₂(DMF)₂]·2H₂O [<b>1</b>], [Cd₃(BPT)₂(DMA)₂] [<b>2</b>], and [(CH₃CH₂)₂NH₂]·[Cd­(BPT)]·2H₂O [<b>3</b>] were obtained by the hydrothermal reaction of a <i>C</i>₂-symmetric tricarboxylate linker, biphenyl-3,4′,5-tricarboxylic acid (H₃BPT), with cadmium nitrate in the mixed solvents of water with <i>N</i>,<i>N</i>-dimethylformamide (DMF), <i>N</i>,<i>N</i>-dimethylacetamide (DMA), diethylformamide (DEF), respectively. Single-crystal X-ray diffraction analyses reveal that complex <b>1</b> is a three-dimensional (3D) network containing infinite Cd–O–Cd chains with the solvent DMF molecule bridging the neighboring Cd1 and Cd2 centers. Though complex <b>2</b> also has a 3D network containing infinite metal-carboxylate chains, the solvent DMA molecule only coordinates to one of the Cd­(II) centers as a terminated solvent molecule. Complex <b>3</b> possesses a two-dimensional (2D) (6, 3) honeycomb type net formed by the mononuclear metal ion and the BPT ligand, which are further stacked in ABAB fashion through π–π interactions into a 3D supramolecular architecture. The effect of solvents on the formation of the coordination networks has been shown in the three compounds obtained, and the distinction of coordination architectures is due to the coordination abilities of solvent molecules with the metal centers. The structure stabilities and photoluminescent properties of the three coordination polymers have also been investigated

Unusual Long-Range Ordering Incommensurate Structural Modulations in an Organic Molecular Ferroelectric

The incommensurate (IC) behaviors of ferroelectrics have been widely investigated in inorganic oxides as an exciting branch for aperiodic materials, whereas it still remains a great challenge to achieve such intriguing effects in organic systems. Here, we present that successive ordering of dynamic dipoles in an organic molecular ferroelectric, <i>N-</i>isopropylbenzylaminium trichloroacetate (<b>1</b>), enables unusual incommensurately modulated structures between its paraelectric phase and ferroelectric phase. In particular, <b>1</b> exhibits three distinct IC states coupling with a long-range ordering modulation. That is, the incommensurately modulated lattice is ∼7 times as large as its periodic prototype, and the IC structure is well solved using a (3 + 1)<i>D</i> superspace group with the modulated wavevector <b><i>q</i></b> = (0, 0, 0.1589). To the best of our knowledge, <b>1</b> is the first organic ferroelectric showing such a long-range ordering IC structural modulation. In addition, structural analyses reveal that slowing down dynamic motions of anionic moieties accounts for its modulation behaviors, which also results in dramatic reorientation of dipolar moments and concrete ferroelectric polarization of <b>1</b> (∼0.65 μC/cm²). The combination of unique IC structural modulations and ferroelectricity makes <b>1</b> a potential candidate for the assembly of an artificially modulated lattice, which will allow for a deep understanding of the underlying chemistry and physics of aperiodic materials