A Molecular Thermochromic Ferroelectric

Molecular ferroelectrics have attracted considerable interests because of their easy and environmentally friendly processing, low acoustical impedance and mechanical flexibility. Herein, a molecular thermochromic ferroelectric, N,N′‐dimethyl‐1,4‐diazoniabicyclo[2.2.2]octonium tetrachlorocuprate(II) ([DMe‐DABCO]CuCl₄) is reported, which shows both excellent ferroelectricity and intriguing thermochromism. [DMe‐DABCO]CuCl₄ undergoes a ferroelectric phase transition from Pca2₁ to Pbcm at a significantly high Curie temperature of 413 K, accompanied by a color change from yellow to red that is due to the remarkable deformation of [CuCl₄]^2? tetrahedron, where the ferroelectric and paraelectric phases correspond to yellow and red, respectively. Combined with multiple bistable physical properties, [DMe‐DABCO]CuCl₄ would be a promising candidate for next‐generation smart devices, and should inspire further exploration of multifunctional molecular ferroelectrics.     

Reversible Interconversion between Luminescent Isomeric Metal–Organic Frameworks of [Cu4I4(DABCO)2] (DABCO=1,4‐Diazabicyclo[2.2.2]octane)

The metal–organic frameworks (MOF) of cluster [Cu₄I₄(DABCO)₂] (DABCO=1,4‐diazabicyclo[2.2.2]octane) have been prepared and characterized as two different crystalline forms, I and II . Form I is obtained by reaction of DABCO and CuI in aqueous solution or by solvothermal reaction, while form II is obtained by reacting DABCO and CuI in acetonitrile. Their luminescence properties in the solid state have been analyzed at room temperature and at 77 K. MOF II has bright emission with a maximum at 556 nm that shifts bathochromically at low temperature in conjunction with a marked change in the colour of the emission. The emission of MOF I has a maximum at 580 nm and a less pronounced temperature dependence. The peculiar luminescence properties of the two isomers have been interpreted by utilising current knowledge on the excited states properties of Cu^I cubane clusters. The two isomers exhibit a high degree of porosity and can release the disordered solvent molecules trapped in the channels, whilst preserving the crystal structure. Isomer I can be converted into II on exposure to acetonitrile or methanol vapour, whereas II reverts to I when heated in a closed pan at 250 °C.     

Hetero Face‐to‐Face Porphyrin Array with Cooperative Effects of Coordination and Host–Guest Complexation

We successfully synthesized a hetero face‐to‐face porphyrin array composed of ZnTPP and RuTPP(DABCO)₂ (TPP: 5, 10, 15, 20‐tetraphenylporphyrin, DABCO: 1,4‐diazabi‐cyclo[2.2.2]octane) in 2:1 molar ratio. A cyclic Zn porphyrin dimer (ZnCP) was also used as the host molecule for the Ru porphyrin. In the latter, the Ru‐DABCO bonding in RuTPP(DABCO)₂ was stabilized by the host‐guest complexation. Reaction progress kinetic analysis of the ligand substitution reaction of RuTPP(DABCO)₂ and that in ZnCP revealed the stabilization mechanism of the Ru‐DABCO bonding. Photoinduced electron transfer (PET) from the Zn porphyrin to the Ru porphyrin was observed in the porphyrin array. The host‐guest stabilization of unstable complex for construction of a donor—acceptor–donor structure is expected to be a new method for an artificial photosynthesis.     

Organic/Bismuth Iodides Hybrids: Structural Perturbation of Substitutes and Their Photocurrent Response Properties

Two new organic/bismuth halides hybrids, (Et₂DABCO)₂(Bi₂I₁₀) (1) and (Pr₂DABCO)₂(Bi₂I₁₀) (2) (Et₂DABCO²⁺ = N, N’-diethyl-1,4-diazabicyclo[2.2.2] octane, Pr₂DABCO²⁺ = N, N’-diproyl-1,4- diazabicyclo[2.2.2] octane) have been synthesized. Both hybrids contain (Bi₂I₁₀)^4? halobismuthate dimers and (Et₂DABCO)²⁺/(Pr₂DABCO)²⁺ cations, and C–H···I hydrogen bonds contribute to the structural extending from 0-d clusters to 2-d layer (for 1) and 3-d network (for 2). Theoretical calculations were conducted to reveal the perturbation effects of 1,4-diazabicyclo[2.2.2] octane substitutes on their structures. Their absorption spectra were investigated, and energy band gaps of 2.10/2.16 eV indicate their narrow-gap semiconductor natures. Their photocurrent response properties were also discussed.     

Reactions of Rare‐Earth Metal Based Lewis Pairs with Azides†

The reactivity of homoleptic rare‐earth metal aryloxide based Lewis pairs toward organic azide substrates has been investigated herein. Treatment of RE(OAr)₃ (RE = La, Sm, Y, and Sc, Ar = 2,6‐^tBu₂‐C₆H₃), PEt₃ and Me₃SiN₃ in 2 : 1 : 1 molar ratio resulted in formation of separated ion pair complexes [Me₃Si‐PEt₃]⁺[(ArO)₃RE‐N=N=N‐RE(OAr)₃]^– under mild conditions. Replacement of phosphine with the nitrogen‐containing Lewis base 1,4‐diazabicyclo[2.2.2]octane (DABCO) produced analogous rare‐earth azide complexes with [Me₃Si‐DABCO]⁺ counterions. In contrast, reaction of the La(OAr)₃/PEt₃ Lewis pair with 1‐adamantyl azide (AdN₃) afforded the typical frustrated Lewis pair‐type 1,1‐addition product. A tetrahydrofuran ring‐opening reaction was also observed for the resulting rare‐earth azide complex with the [Me₃Si‐PEt₃]⁺ cation, with cleavage of the C—O bond by Si/P cooperation.     

Sulfonylation of 1,4-Diazabicyclo[2.2.2]octane: Charge-Transfer Complex Triggered C−N Bond Cleavage

A novel charge-transfer complex triggered sulfonylation of 1,4-diazabicyclo[2.2.2]octane (DABCO) with mild reaction conditions has been developed. The formation of a charge-transfer complex between electron-withdrawing (hetero)aryl sulfonyl chloride and DABCO allows the synthesis of N-ethylated piperazine sulfonamide in good yields. The reaction has a high functional group tolerance. Spectroscopic studies confirmed the charge-transfer complex formation between sulfonyl chlorides and DABCO, which facilitates the C−N bond cleavage of DABCO.     

Amide bond formation using an air-stable source of AlMe3

Synthesis of amides from coupling esters with a range of primary amines can be conveniently achieved in moderate to excellent yields (69-99%) using an air-stable adduct of trimethylaluminium (AlMe₃)₂·DABCO (DABCO is 1,4-diazobicyclo[2.2.2]octane), referred to as DABAL-Me₃. Reactions can be run without requiring the exclusion of atmospheric oxygen or the drying of solvents.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

A simple and convenient synthesis of [1,2,4]triazolo/benzimidazolo ‎quinazolinone and [1,2,4]triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidine derivatives catalyzed by ‎DABCO-based ionic liquids

DABCO-based ionic liquids were utilized for the preparation of [1,2,4]triazolo/benzimidazolo quinazolinone and [1,2,4]triazolo[1,5-a]pyrimidine derivatives in the adequate procedures. These methods involve three-component reaction between aldehydes, β-diketones and 3-amino-1,2,4-triazole or 2-aminobenzimidazole in the presence of 1,4-disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium chloride ([DABCO](SO₃H)₂(Cl)₂) and 1,4-disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen sulfate ([DABCO](SO₃H)₂(HSO₄)₂) as reusable and economical catalysts at 100 °C. These methods also show eco-friendly characters by elimination of solvent. Any by-product was not prepared through this method, and products were separated by a simple workup procedure. The other noticeable benefits of these procedures are excellent yields, short reaction times, mild reaction conditions and use of available and inexpensive materials.     

2，7-萘二磺酸导向构筑的五元瓜环-碱金属及碱土金属基超分子自组装体及其溶剂识别

以2,7-萘二磺酸（2,7-H₂NDA）作为结构导向剂,与五元瓜环（Q[5]）和碱金属、碱土离子（K⁺、Rb⁺、Mg²⁺、Ca²⁺）在水热条件下制备出了4种新颖的Q[5]基超分子自组装体[K₂（H₂O）₄（Q[5]）]（2,7-NDA）·4H₂O （1）、[Rb₂（H₂O）₅（Q[5]）]（2,7-NDA）·3H₂O （2）、[Mg （H₂O）₄（Q[5]）]（2,7-NDA）·8H₂O （3）和[Ca （H₂O）₄（Q[5]）]（2,7-NDA）·10H₂O （4）。单晶X射线衍射测试结果表明,自组装体1和2具有相同的结构： Q[5]分子与金属离子配位形成的是“分子胶囊”;而在3中Q[5]与Mg²⁺配位形成的是1：1型简单配合物结构;在自组装体4中,Q[5]与Ca²⁺配位形成的是一维Q[5]-Ca²⁺配位聚合物链结构。这些结构中2,7-NDA^2-阴离子平衡了体系电荷,且通过其与瓜环外壁之间的弱相互作用,促进自组装体最终构筑成三维超分子结构。此外,还研究了自组装体4的溶剂识别荧光传感性能,结果表明其能够作为有机溶剂丙酮和DMF的猝灭型荧光探针。     

pH-Dependent Syntheses,Crystal Structures and Properties of Three Low-Dimensional Iodoargentate Hybrids

By simply changing pH value of reaction solution, three low-dimensional iodoargentate hybrids, [HDABCO]₂[(DABCO)₂(Ag₂I₄)] (1), [HDABCO]_0.5[(HDABCO)_0.5(AgI₂)] (2) and [(Me₂NH₂)(H₂DABCO)][AgI₄] (3) (DABCO = 1,4-diazabicyclo-[2.2.2]octane), have been synthesized. Noteworthy, variation in protonated degree and aggregating forms of DABCO at different pH value, the structure of inorganic moieties vary regularly from 0D [(DABCO)₂(Ag₂I₄)]^2? anion for 1 to 1D [(HDABCO)_0.5(AgI₂)]^0.5? chain for 2 and 0D [AgI₄]^3? anion for 3, exhibiting unique structural directing effects. In addition, three compounds display structure-dependent semiconductor natures and thermal stabilities.     

Synthesis of β‐Keto Sulfones by a Catalyst‐Free Reaction of Aryldiazonium Tetrafluoroborates,Sulfur Dioxide,and Silyl Enol Ethers

A green approach for the generation of β‐keto sulfones through a reaction of aryldiazonium tetrafluoroborates and sulfur dioxide with silyl enol ether under catalyst‐ and additive‐free conditions has been realized. This reaction proceeds efficiently at room temperature and goes to completion in half an hour. During the reaction process, aryldiazonium tetrafluoroborate is treated with DABCO ⋅ (SO₂)₂ (DABCO=1,4‐diazabicyclo[2.2.2]octane) to provide a sulfonyl radical as the key intermediate, which then initiates the transformation. Oxidants or metal catalysts are avoided, and the presence of DABCO also plays an important role in the reaction.     

Effect of the Metal within Regioisomeric Paddle-Wheel-Type Metal–Organic Frameworks

The effect of metal on the degree of flexibility upon evacuation of metal–organic frameworks (MOFs) has been revealed with positional control of the organic functionalities. Although Co-, Cu-, and Zn-based DMOFs (DMOF = DABCO MOF, DABCO = 1,4-diazabicyclo[2.2.2]octane) with ortho-ligands (2,3-NH₂Cl) have frameworks that are inflexible upon evacuation, MOFs with para-ligands (2,5-NH₂Cl) showed different N₂ uptake amounts after evacuation by metal exchange. Considering that the structural analyses were not fully sufficiently different to explain the drastic changes in N₂ adsorption after evacuation, quantum chemical simulation was explored. A new index (η) was defined to quantify the regularity around the metal based on differences in the oxygen-metal-oxygen angles. Within 2,5-NH₂Cl, the η value becomes larger as the metal are varied from Co to Zn. A large η value means that the structures around the metal center are less ordered. These results can be used to explain flexibility changes upon evacuation by altering the metal cation in this regioisomeric system.     

Chemical Stimulus‐responsive Folding and Unfolding of a Dendrimeric Assembly

A dendrimeric trimer undergoes folding and unfolding in response to a chemical stimulus. The trimer of interest contains a central dendrimer with a butadiyne‐linked zinc porphyrin dimer ((ZnP)₂) core, in addition to two terminal dendrimers with zinc porphyrin (ZnP) cores. The obtained absorption spectra indicate that the unfolded form is the exclusive conformer in chloroform, while the addition of 1,4‐diazabicyclo[2.2.2]octane (DABCO) in chloroform leads to transformation from the unfolded to the folded structure containing two DABCO units per trimer; the folded structure originates from the cross‐linking of (ZnP)₂ and ZnP with DABCO. Moreover, the addition of excess DABCO promotes the generation of the unfolded structure containing four DABCO units.     

Crystal structure,optical properties,and theory study of a 1-D bromoplumbate stabilized by in situ generated N-alkylated DABCO cation

We report the exploration of the stabilization effect of the in situ generated N-alkylated DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane) cation in the family of bromoplumbates and a 1-D bromoplumbate, (Et₂DABCO)_2n(Pb₃Br₁₀)_n (1), has been prepared by solvothermal conditions. Optical diffuse reflectance determination shows the band gap of 1 is 3.69 eV, which manifests that 1 is a wide band gap semiconductor. Compared with the band gap of bulk PbBr₂ (3.84 eV), 1 exhibits 0.15 eV red shift of absorption edge. While for the reported iodo analogs of this compound, (MPDA)_2n(Pb₃I₁₀)_n and (Et₂DABCO)_2n(Pb₃I₁₀)_n, they exhibit 0.53 and 0.47 eV blue shift of the energy gaps compared with the measured value of 2.30 eV for bulk PbI₂, respectively. The photoluminescent study of 1 shows that it exhibits a broad emission band centered at 697 nm upon photoexcitation by 345 nm (amount to 3.59 eV). The calculated density of states manifests the theoretical value of the band gap of 1 is 3.422 eV and the origination of photoluminescence can be ascribed to the transition of bonding electrons of Br^– anion to the empty orbits of Pb(II) ion.     

Synthesis of optically active hydridocarbonyl triosmium clusters with terpene derivatives as ligands. Molecular structure and absolute configuration of a cluster with a bridging dihydroimidazole ligand

Reactions of the triosmium clusters Os₃(CO)₁₁(NCMe) (1) and Os₃(CO)₁₀(NCMe)₂ (2) with terpene derivatives,viz., (1S,3S,4R,6R)-3-(N,N-dimethylamino)-4-amino-3,7,7-trimethylbicyclo [4.1.0]heptane (3). (3bR,4aR)-(3,4,4-trimethyl-3b,4,4a,5-tetrahydrocyclopropa [3,4]cyclopenta[1,2-c]pyrazol-1-yl)acetic acid (4a), and (3bR,4aR)-3-(3,4,4-trimethyl-3b, 4,4a,5-tetrahydrocyclopropa[3,4]cyclopenta[1,2-c]pyrazol-1-yl)propionic acid (4b), were studied. A complex with the terminally coordinated ligand is formed in the first step of the reaction of diamine3 with cluster1. Heating of the resulting complex is accompanied by activation of one of the methyl groups of the ligand to form diastereomers with the bridging tricyclic dihydroimidazole ligand. One of these diastereomers was studied by X-ray diffraction analysis and its absolute configuration was established. Pyrazolycarboxylic acids react with cluster2 as simple organic acids and are coordinated as a bridge at the Os—Os bond through the carboxyl group. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1447–1454, August, 2000.     

Polymorphs of DABCO monohydrate as structural analogues of NaCl

A new crystalline form of 1,4‐diazabicyclo[2.2.2]octane (DABCO) monohydrate, C₆H₁₂N₂·H₂O, crystallizing in the space group P3₁, has been identified during screening for cocrystals. There are three DABCO and three water molecules in the asymmetric unit, with two DABCO molecules exhibiting disorder over two positions related by rotation around the N...N axis. As in the monoclinic C2/c (Z′ = 2) polymorph, the molecular components are connected via O—H...N hydrogen bonds into a polymeric structure that consists of linear O—H...N(CH₂CH₂)₃N...H—O segments, which are approximately mutually perpendicular. The two polymorphic forms of DABCO monohydrate can be considered as structural analogues of NaCl, with the nearly globular DABCO molecules showing distorted cubic closest packing and all octahedral interstices occupied by water molecules.     

Potential of bifluorenylidene derivatives as nonfullerene small-molecule acceptor for heterojunction organic photovoltaics: a density functional theory study

To maximize the efficiency of heterojunction organic photovoltaics (HJOPVs), it is imperative to increase not only the open-circuit voltage (V _OC) but also the short-circuit current (I _SC). Therefore, it is desirable to find an organic acceptor material that possesses a higher lowest unoccupied molecular orbital (LUMO) level for higher V _OC and can absorb photons in the solar spectrum efficiently for larger I _SC. In this paper, in comparison with the typical donor poly(3-hexylthiophene) (P3HT) and acceptor [6,6]-phenyl-C₆₁-butyric acid ester ([60]PCBM), the geometries, electronic structures, absorption spectra, and transport properties of a series of organic compounds containing 9,9′-bifluorenylidene (9,9′BF) were systematically investigated using density functional and the semiclassical Marcus charge transfer theory calculation to evaluate their potential severing as acceptor. Our results indicate that the absorption spectra of 99′BF derivatives have better overlap with the solar spectrum than those of [60]PCBM, and higher LUMOs result in a significant enhancement of V _OC when they are used in HJOPVs with P3HT as donor materials. On the other hand, these compounds own higher electron carrier mobilities comparing with [60]PCBM. The study also demonstrates that the H-shaped compounds based on the 99′BF backbone possess good photophysical and charge transport properties, can be promising organic semiconductor for heterojunction photovoltaics.     

Pd(OAc)2/DABCO-catalyzed Suzuki-Miyaura cross-coupling reaction in DMF

The scope and limitations of the Pd(OAc)₂/DABCO (1,4-diaza-bicyclo[2.2.2]octane)-catalyzed Suzuki-Miyaura cross-coupling reactions have been demonstrated. The results showed that the effect of solvent had a fundamental influence on the reaction. In the presence of Pd(OAc)₂ and DABCO, both aryl bromides and aryl chlorides all worked well with arylboronic acids to form biaryls, heteroaryl-aryls, and biheteroaryls in moderate to excellent yields using DMF as the solvent. Additionally, the reactions of aryl bromides were conducted under relatively mild conditions.     

Alkaline Earth Metal Template (Cross-)Coupling Reactions with Hybrid Disila-Crown Ether Analogues

Alkaline earth metal iodides were used as templates for the synthesis of novel silicon-based ligands. Siloxane moieties were (cross-)coupled and ion-specific, silicon-rich crown ether analogues were obtained. The reaction of 1,2,7,8-tetrasila[12]crown-4 ( I ) and 1,2-disila[9]crown-3 ( II ) with MgI₂ yielded exclusively [Mg(1,2,7,8-tetrasila[12]crown-4)I₂] ( 1 ). The larger Ca²⁺ ion was then employed for cross-coupling of I and II and yielded the complex [Ca(1,2,7,8-tetrasila[15]crown-5)I₂] ( 2 ). Cross-coupling of I and 1,2,4,5-tetrasila[9]crown-3 ( III ) with SrI₂ enables the synthesis of the silicon-dominant 1,2,4,5,10,11-hexasila[15]crown-5 ether complex of SrI₂ ( 3 ). Further, the compounds [Sr(1,2,10,11-tetrasila[18]crown-6)I₂] ( 4 ), [Sr(1,2,13,14-tetrasila[24]crown-8)I₂] ( 5 ), and [Sr(1,2,13,14-tetrasila-dibenzo[24]crown-8)I₂] ( 6 ) were obtained by coupling I , 1,2-disila[12]crown-4 ( IV ) or 1,2-disila-benzo[12]crown-4 ( V ), respectively. Using various anions, the (cross-)coupled ligands were also observed in an X-ray structure within the mentioned complexes. These template-assisted (cross-)couplings of various ligands are the first of their kind and a novel method to obtain macrocycles and/or their metal complexes to be established. Further, the Si−O bond activations presented herein might be of importance for silane or even organic functionalization.