Solid-state Spectra Research Articles

Rare earth inorganic-organic hybrid compounds based on Keggin-type polyoxometalate {SiW12} with fast-responsive photochromism and switchable luminescence properties

Four rare earth inorganic-organic hybrid compounds based on Keggin-type polyoxometalate {SiW12} with general formula [{RE(DMF)4(H2O)4RE(DMF)6}2{SiW12O40}3] (RE = La(1), Pr(2), Sm(3), Eu(4), DMF = N,N-dimethylformamide) were synthesized by the conventional solution method. Structure analyses indicate that four compounds are isostructural and are all built from three [SiW12O40]4– polyoxoanions and DMF ligands linked by RE3+. Compounds 1–4 are extremely sensitive to UV light and present excellent photochromic properties, in which the coloring and fading time of samples are both no more than 2 min, and the reversible coloring-fading process can be repeated for at least 10 cycles with little fatigue, suggesting that compounds 1–4 can be a series of fast-responsive and durable photochromic materials. Moreover, the solid-state photoluminescence spectra of compounds 3(Sm) and 4(Eu) display strong characteristic emissions of rare earth ions based on f–f transitions. Meanwhile, compound 4(Eu) has a longer fluorescence lifetime up to 566.74 μs. Notably, compounds 3(Sm) and 4(Eu) exhibit the switchable luminescence behavior induced by photochromism, which allows them to be used as potential molecular switches.

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

Resolving a Half-Century-Long Controversy between (Magneto)optical and EPR Spectra of Single-Electron-Reduced [PcFe]-, [PcFeL]-, and [PcFeX]2- Complexes: Story of a Double Flip.

The reduction of iron(II) phthalocyanine (Pc(2-)FeII) or its bisaxially coordinated complexes results in the formation of the purple/red [PcFe]-, [PcFeL]-, and [PcFeX]2- (L is neutral and X is anionic ligand) species. The X-ray structure of the [K(DME)4][PcFe] complex exhibits a square-planar [PcFe]- anion. 1H NMR spectra of the reduced species have one or two phthalocyanine broad peaks between 15 and 17 ppm. Solution magnetic moments are consistent with the presence of a single unpaired electron. A solid-state Mössbauer spectrum of [K(DME)4][PcFe] is consistent with an early report [Taube, R. Pure Appl. Chem.1974, 38, 427-438]. The solid-state EPR spectrum of the [PcFe]- anion is close to that recorded by Konarev et al. [ Dalton Trans.2012, 41, 13841-13847]. Solution EPR spectra of reduced species have axial symmetry (g⊥ ∼ 2.08-2.17 and g|| ∼ 1.95-1.96) and correlate well with spectra reported by Lever and Wilshire in 1978 [ Inorg. Chem.1978, 17, 1145-1151]. The UV-vis spectra of pentacoordinated [PcFeL]- and [PcFeX]2- anions consist of the characteristic bands around 810, 690, and 515 nm. These bands correlate well with the set of MCD pseudo A-terms and resemble transitions in the [Pc(3-)M]- and [Pc(3-)ML]- compounds. The UV-vis and MCD spectra of [PcFeL]- and [PcFeX]2- complexes are in stark contrast to the crystallographically characterized reference [Pc(2-)CoI]- anion, which is EPR silent, has a regular diamagnetic 1H NMR spectrum, and has an intense Q-band at 699 nm, which correlates well with the strong MCD A-term. The DFT and TDDFT calculations are suggestive of the iron(II) center in a (dxy)2(dxz,yz)3(dz2)1 (s = 1) electronic configuration that is antiferromagnetically coupled with the one-electron-reduced Pc(3-) ligand (i.e., [Pc(3-)FeII]-, [Pc(3-)FeIIL]-, and [Pc(3-)FeIIX]2-). The calculated EPR, Mössbauer, and UV-vis spectra of [PcFe]-, [PcFeL]-, and [PcFeX]2- complexes are in excellent agreement with the experimental data, thus resolving the controversy between axial s = 1/2 like EPR and Pc(3-)-like UV-vis spectra of these compounds.

Two coordination polymers assembled with resorcin[4]arenes ligand: Luminescent sensing Fe3+ ion and Cr2O72− anion

Two coordination polymers, [Cd2L(btbp)0.5(DMF)(H2O)]·3DMF (1) and [Zn2L(btbp)0.5(H2O)2]·DMF·3H2O (2) have been synthesized base on resorcin[4]arene, btbp and metal ions in solvothermal conditions (H4L = 2,8,14,20-tetra-ethyl-4,10,16,22-tetrakis(4-carboxybenzyl)oxy)-6,12,18,24-tetra-methoxy-resorcin[4]arene, btbp = 4,4′-bis(1,2,4-triazole-1-ylmethyl)biphenyl)). The structures of CPs 1 and 2 were determined by single-crystal X-ray diffractometer. Structural analysis shows that 1 and 2 exhibit layer structures. CPs 1 and 2 were characterized by Fourier transform infrared spectroscopy (FTIR), Powder X-ray diffraction (PXRD), elemental analysis and UV–vis Spectra. The solid-state emission spectra of 1 and 2 have been carried out and exhibit emission peaks at 452 nm (λex = 364 nm) and 455 nm (λex = 371 nm), respectively. Remarkably, CPs 1 and 2 exhibit excellent luminescent emissions in solid-state. Furthermore, CP 1 was used to detect Fe3+ and Cr2O72− in aqueous solution, and its sensitivity and anti-interference were also studied. The Stern-Volmer constant Ksv were 4.381 × 103 M−1and 1.1109 × 104 M−1, respectively. Further analysis showed that the quenching of CP 1 might be related to the energy competition of Fe3+ and Cr2O72−.

Highly selective epoxidation of styrene at ambient temperature under photo-assisted condition over bimetallic Eu and Ti-doped amino-functionalized mesoporous molecular sieve

Mesoporous molecular sieves silica materials had been functionalized employing 3-aminopropyltriethoxysilane as the surface decoration agent by a post-synthesis method and Eu and Ti with different loading ratio were synchronously anchored on amino-functionalized silica framework by incipient wetness impregnation method, respectively. The structures of the synthesized samples were evaluated by means of X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectra, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and solid-state 29Si magic angle spinning nuclear magnetic resonance spectra. The results revealed that the highly ordered mesoporous two dimensional hexagonal structure and the mesoporous channel structure were well preserved and isolated tetrahedral surface Eu3+ and isolated [TiO4] or [HOTiO3] species were found to be grafted and highly dispersed in the amino-functionalized mesoporous framework. A significant enhancement in selectivity and conversion for the photocatalytic epoxidation of styrene has been achieved by synergistic effect based on surface ligand effect and electron density effect between Eu3+ and Ti4+ species on amino-functionalized mesoporous silica framework. The factors associated with the conversion of styrene and selectivity to styrene oxide such as the solvent, metal loading, the amount of NaOH, H2O2/Styrene, the amount of catalyst and reaction time were also investigated in details. The desired selectivity (84%) to styrene oxide and excellent conversion (32%) of styrene for the photocatalytic epoxidation of styrene with turnover frequency of 3.1 × 10−4s−1 were obtained using aqueous H2O2 as an oxidant in the presence of acetonitrile solvent under ambient temperature.

Synthesis, Characterization, and Cytotoxicity Studies of N-(4-Methoxybenzyl) Thiosemicarbazone Derivatives and Their Ruthenium(II)-p-cymene Complexes.

The reaction of [Ru2Cl2(μ-Cl)2(η6-p-cymene)2] with two thiosemicarbazones obtained by the condensation of N-(4-methoxybenzyl) thiosemicarbazide and 1,4-hydroxy-3-methoxyphenyl)ethan-1-one (HL1) or 2-fluoro-4-hydroxybenzaldehyde (HL2) was studied. The cationic complexes of formula [RuCl(η6-p-cymene)(HL)]+ were isolated as solid chloride and trifluoromethylsulfate (TfO) salts. A study of the solid state and NMR spectra suggests the presence in the material of two isomers that differ in the configuration in the iminic bond, C2=N3, of the coordinated thiosemicarbazone in the triflate salts and only the E isomer in the chloride. An X-ray study of single crystals of the complexes supports this hypothesis. The thiosemicarbazone ligand coordinates with the ruthenium center through the iminic and sulfur atoms to form a five-membered chelate ring. Furthermore, the isolation of single crystals containing the thiosemicarbazonate complex [Ru2(μ-L2)2(η6-p-cymene)2]2+ suggests the easy labilization of the coordinated chloride in the complex. The redox behavior of the ligands and complexes was evaluated by cyclic voltammetry. It seems to be more difficult to oxidize the complex derived from HL1 than HL2. The ability of the complexes to inhibit cell growth against the NCI-H460, A549 and MDA-MB-231 lines was evaluated. The complexes did not show greater potency than cisplatin, although they did have greater efficacy, especially for the complex derived from HL1.

Influence of Tartrate Ligand Coordination over Luminescence Properties of Chiral Lanthanide-Based Metal-Organic Frameworks.

The present work reports on a detailed discussion about the synthesis, characterization, and luminescence properties of three pairs of enantiopure 3D metal-organic frameworks (MOFs) with general formula {[Ln2(L/D-tart)3(H2O)2]·3H2O}n (3D_Ln-L/D, where Ln = Sm(III), Eu(III) or Gd(III), and L/D-tart = L- or D-tartrate), and ten pairs of enantiopure 2D coordination polymers (CPs) with general formula [Ln(L/D-Htart)2(OH)(H2O)2]n (2D_Ln-L/D, where Ln = Y(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III) or Yb(III), and L/D-Htart = hydrogen L- or D-tartrate) based on single-crystal X-ray structures. Enantiopure nature of the samples has been further corroborated by Root Mean Square Deviation (RMSD) as well as by circular dichroism (CD) spectra. Solid-state emission spectra of Eu(III), Tb(III), and Dy(III)-based compounds confirm the occurrence of ligand-to-metal charge transfers in view of the characteristic emissions for these lanthanide ions, and emission decay curves were also recorded to estimate the emission lifetimes for the reported compounds. A complete theoretical study was accomplished to better understand the energy transfers occurring in the Eu-based counterparts, which allows for explaining the different performances of 3D-MOFs and 2D-layered compounds. As inferred from the colorimetric diagrams, emission characteristics of Eu-based 2D CPs depend on the temperature, so their luminescent thermometry has been determined on the basis of a ratiometric analysis between the ligand-centered and Eu-centered emission. Finally, a detailed study of the polarized luminescence intensity emitted by the samples is also accomplished to support the occurrence of chiro-optical activity.

Highly Strained Arene-Fused 1,2-Diborete Biradicaloid.

The stepwise reduction of a doubly cyclic alkyl(amino)carbene (CAAC)-stabilized 2,3-bis(dibromoboryl)naphthalene enables the isolation of the corresponding mono- and bis(boryl) radicals (one- and two-electron reduction), a 2π-aromatic 1,2-diborete (four-electron reduction), which shows biradical character in the solid-state EPR spectrum, and its cyclic bis(alkylidene)diboron dianion (six-electron reduction). The X-ray crystallographic analysis of the diborete shows a highly strained and twisted four-membered ring with a formal cis-diborene motif featuring a very elongated B-B double bond. Calculations based on DFT and multireference approaches reveal that the diborete possesses an open-shell singlet biradicaloid ground state, which is slightly energetically preferred to its EPR-active triplet-state congener. The addition of CO to the diborete resulted in B-B bond splitting and the formation of the corresponding closed-shell singlet, doubly Lewis base-stabilized bis(borylene), whereas a twofold γ insertion of phenyl azide generates a 1,3-bis(diazenyl)-1,3,2,4-diazadiboretidine.

Use chloride to assist in constructing of penta- and nano-nucleus mixed-valent Cu(I/II) clusters and their photo-thermal properties

To prepare new series of mixed-valence polynuclear Cu(I/II) clusters, chloride ions are introduced to construct two mixed-valence polynuclear Cu(I/II) clusters for evaluating their photothermal conversion performance. X-ray single-crystal structural analysis reveals their molecular formula are {CuII[CuI(Cy3P)]4(BTA)4Cl2}·5DMF (I·5DMF, Cy3P = triscyclohexylphosphine, BTA = benzotriazole, DMF = N,N-Dimethylformamide) and {(CuII)3[CuI(PPh2Py)]6(BTA)8Cl4}·6DMF (II·6DMF, Ph2PyP = diphenyl-2-pyridylphosphine), respectively. X-ray Photoelectron Spectroscopy (XPS) and Electrospray Ionization Mass Spectrometry (ESI-MS) confirm their chemical composition and charge state. The reported two mixed-valence CuI/CuII clusters have different nucleus (penta-nucleus for I and nano-nucleus for II) and different proportion of valence state (1/4 for I vs 1/2 for II). The thermogravimetric analysis (TGA) reveals the thermal stability of both clusters is less than our previously reported penta-nucleus mixed-valence CuI/CuII clusters. Contrastively studies of their optical absorption properties by the solid-state ultraviolet diffuse reflection spectra indicate high-nucleus mixed-valence CuI/CuII cluster with higher proportion of CuII is superior to those penta-nucleus mixed-valent Cu(I/II) clusters. With the introduction of chloride ions to the structures of mixed-valence CuI/CuII clusters have not remarkably changed their photothermal conversion performance. This study provides a practicable way to construct new mixed-valence CuI/CuII clusters with different photothermal conversion performance.

Cationic Nickel d9‐Metalloradicals [Ni(NHC)2]+

AbstractA series of five new homoleptic, linear nickel d9‐complexes of the type [NiI(NHC)2]+ is reported. Starting from the literature known Ni(0) complexes [Ni(Mes2Im)2] 1, [Ni(Mes2ImH2)2] 2, [Ni(Dipp2Im)2] 3, [Ni(Dipp2ImH2)2] 4 and [Ni(cAACMe)2] 5 (Mes2Im=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolin‐2‐ylidene, Mes2ImH2=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolidin‐2‐ylidene, Dipp2Im=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene, Dipp2ImH2=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolidin‐2‐ylidene, cAACMe=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐yliden), their oxidized Ni(I) analogues [NiI(Mes2Im)2][BPh4] 1+, [NiI(Mes2ImH2)2][BPh4] 2+, [NiI(Dipp2Im)2][BPh4] 3+, [NiI(Dipp2ImH2)2][BPh4] 4+ and [NiI(cAACMe)2][BPh4] 5+ were synthesized by one‐electron oxidation with ferrocenium tetraphenyl‐borate. The complexes 1+–5+ were fully characterized including X‐ray structure analysis. The complex cations reveal linear geometries in the solid state and NMR spectra with extremely broad, paramagnetically shifted resonances. DFT calculations predicted an orbitally degenerate ground state leading to large magnetic anisotropy, which was verified by EPR measurements in solution and on solid samples. The magnetic anisotropy of the complexes is highly dependent from the steric protection of the metal atom, which results in a noticeable decrease of the g‐tensor anisotropy for the N‐Mes substituted complexes 1+ and 2+ in solution due to the formation of T‐shaped THF adducts.

Removal of Model Aromatic Hydrocarbons from Aqueous Media with a Ferric Sulfate–Lime Softening Coagulant System

The removal of model hydrocarbon oil systems (4-nitrophenol (PNP) and naphthalene) from laboratory water was evaluated using a ferric sulfate and a lime-softening coagulant system. This study addresses the availability of a methodology that documents the removal of BTEX related compounds and optimizes the ferric-based coagulant system in alkaline media. The Box–Behnken design with Response Surface Methodology enabled the optimization of the conditions for the removal (%) of the model compounds for the coagulation process. Three independent variables were considered: coagulant dosage (10–100 mg/L PNP and 30–100 mg/L naphthalene), lime dosage (50–200%), and initial pollutant concentration (1–35 mg/L PNP and 1–25 mg/L naphthalene). The response optimization showed a 28% removal of PNP at optimal conditions: 74.5 mg/L ferric sulfate, 136% lime dosage, and initial PNP concentration of 2 mg/L. The optimal conditions for naphthalene removal were 42 mg/L ferric sulfate, 50% lime dosage, and an initial concentration of naphthalene (16.3 mg/L) to obtain a 90% removal efficiency. The coagulation process was modeled by adsorption isotherms (Langmuir for PNP; Freundlich for Naphthalene). The surface properties of flocs were investigated with pHpzc, solid-state UV absorbance spectra, and optical microscopy to gain insight into the role of adsorption in the ferric coagulation process.

Rod-shaped cyanoacrylic derivatives with D-π-A architecture: synthesis, thermal, photophysical and theoretical studies

ABSTRACT Two dyes, 4 and 5, bearing an alkoxy group as a donor connected to cyanoacrylic acid acceptor/anchoring group bridged by the phenylacetylene unit were designed and synthetised through Knoevenagel condensation between aromatic aldehydes and cyanoacetic acid reagent. The dyes were characterised using FT-IR, 1H-NMR, 13C-NMR, ESI-HRMS and polarised optical microscopy, absorption and fluorescence techniques. Nematic mesophase was identified for both rod-shaped dyes. During heating at high temperatures (>200°C), the dyes exhibited marked thermal instability which resulted in material decomposition. The photophysical properties of the compounds were investigated in chloroform as well as their absorption, emission spectra in solid state. Solvatochromism was analysed and the mechanism of fluorescence quenching was performed using fullerene pyrrolidine tris-acid ethyl ester PyC 60 as a receptor. The fluorescence quenching studies suggested charge transfer process from dyes 4 and 5 to PyC 60 , where the bimolecular rate constant k q was larger for 4 than 5, showing that the phenyl group performed better than the naphthyl group. The energy band gap predicted with DFT calculations agreed with the experimental data. Natural transition orbitals (NTOs) analysis revealed that S1 states for 4 and 5 in gas phase have a predominantly local-excitation (LE) nature.

Solvent effects on the luminescent properties based on bis(hydroxy-naphthoic acid): Syntheses, crystal structure and Hirshfeld analysis

A set of novel compounds based on bis(hydroxyl-naphthoic acid), namely, B26·G [G = N,N-dimethyl formamide (1), N,N-dimethyl acetamide (2), and N-methyl pyrrolidone (3) (B26= 5,5′-methylene bis(6-hydroxy-2-naphthoic acid) were obtained through the solvent evaporation method, respectively. The title compounds 1-3 have been characterized by IR, UV–Vis, element analysis (EA), single crystal X-ray diffraction, and powder X-ray diffraction (PXRD). In these compounds, a plenty of C/O–H⋯O hydrogen bonds can be obviously obtained. There exist trans- and cis-conformation for two naphthoic carboxylic moieties. The host B26 frameworks show the feature of nonporous adaptive compound enclathrating different guest molecules. The solid-state luminescent spectra of 1-3 show that the emission maxima are observed at 432, 393 and 388 nm, respectively. The decay lifetimes can be found to be 0.42, 0.44 and 0.36 ns for compounds 1-3, respectively. Additionally, the quantum yields of compounds 1-3 are 0.02%, 8.76% and 6.74%, respectively. The Hirshfeld surface analysis reveals that the order of the C···H/H···C and C···C closes contact is in a good agreement with that of the luminescent peaks. The experiment of solvent exchange reveals that the B26 host framework shows low crystal-state stability. Additionally, the thermal behaviors of compounds 1-3 have been discussed in detail.

Zwitterionic and Anionic Polycarboxylates as Coligands in Uranyl Ion Complexes, and Their Influence on Periodicity and Topology.

The three zwitterionic di- and tricarboxylate ligands 1,1'-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-4-carboxylate) (pL1), 1,1'-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-3-carboxylate) (mL1), and 1,1',1″-[(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)]tris(pyridin-1-ium-4-carboxylate) (L2) have been used as ligands to synthesize a series of 15 uranyl ion complexes involving various anionic coligands, in most cases polycarboxylates. [(UO2)2(pL1)2(cbtc)(H2O)2]·10H2O (1, cbtc4- = cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate) is a discrete, dinuclear ring-shaped complex with a central cbtc4- pillar. While [UO2(pL1)(NO3)2] (2), [UO2(pL1)(OAc)2] (3), and [UO2(pL1)(HCOO)2] (4) are simple chains, [(UO2)2(mL1)(1,3-pda)2] (5, 1,3-pda2- = 1,3-phenylenediacetate) is a daisy chain and [UO2(pL1)(pdda)]3·10H2O (6, pdda2- = 1,2-phenylenedioxydiacetate) is a double-stranded, ribbon-like chain. Both [UO2(pL1)(pht)]·5H2O (7, pht2- = phthalate) and [(UO2)3(mL1)(pht)2(OH)2] (8) crystallize as diperiodic networks with the sql topology, the latter involving hydroxo-bridged trinuclear nodes. [(UO2)2(pL1)(c/t-1,3-chdc)2] (9, c/t-1,3-chdc2- = cis/trans-1,3-cyclohexanedicarboxylate) and [UO2(pL1)(t-1,4-chdc)]·1.5H2O (10, t-1,4-chdc2- = trans-1,4-cyclohexanedicarboxylate) are also diperiodic, with the V2O5 and sql topologies, respectively. Both [(UO2)2(mL1)(c/t-1,4-chdc)2] (11) and [(UO2)2(pL1)(1,2-pda)2] (12, 1,2-pda2- = 1,2-phenylenediacetate) crystallize as diperiodic networks with hcb topology, and they display threefold parallel interpenetration. [HL2][(UO2)3(L2)(adc)3]Br (13, adc2- = 1,3-adamantanedicarboxylate) contains a very corrugated hcb network with two different kinds of cells, and the uncoordinated HL2+ molecule associates with the coordinated L2 to form a capsule containing the bromide anion. [(UO2)2(pL1)(kpim)2] (14, kpim2- = 4-ketopimelate) is a three-periodic framework with pL1 molecules pillaring fes diperiodic subunits, whereas [(UO2)2(L2)2(t-1,4-chdc)](NO3)1.7Br0.3·6H2O (15), the only cationic complex in the series, is a triperiodic framework with dmc topology and t-1,4-chdc2- anions pillaring fes diperiodic subunits. Solid-state emission spectra and photoluminescence quantum yields are reported for all complexes.

Preparation, crystal structure, luminescence and Hirshfeld surface of hydroxynaphthene-based compounds

To explore the new luminescent materials, two compounds based on hydroxynaphthene group have been prepared. Compound 2 was synthesized through the esterification of compound 1 in the acid conditions. They have been characterized by IR, EA and single crystal X-ray diffraction. Single X-ray diffraction reveals that compounds 1 and 2 belong to the P21/n and P21/c, respectively. It is obviously observed that there exist C/OH⋯O and the packing interactions among the aromatic rings. The solid-state fluorescent spectra reveal that the maxima of compounds 1 and 2 are 448 and 415 nm, respectively. The luminescent emission maxima are in accordance with the stacking interactions of compounds. The melting points of both compounds can be found to be 190–192 °C and 78–80 °C, respectively. The Hirshfeld surface analysis further reveals that the close contacts C⋯C are responsible for the luminescent peaks, and the O⋯H/H⋯O close bonds can account for the melting points of both compounds.

Biased Al distribution of high-silica FAU-type zeolite synthesized by fast manner at high temperature

The flexible control of composition and atomic arrangement is the ultimate goal in materials science. The control of the Si/Al ratio and Al distribution in the zeolite framework is a hot research topic in the field of zeolites, particularly for catalytic applications. To date, the direct synthesis of high-silica faujasite zeolites (FAUs) with a Si/Al ratio higher than 5 has been limited so far, which is desired to achieve high catalytic performance in various processes such as fluid catalytic cracking and hydrocracking catalysts. In addition, the Al distribution in high-silica FAU has been rarely discussed. In this study, we rapidly synthesized a high-silica FAU with a Si/Al ratio of approximately 6 using tetrapropylammonium cations and seed crystals at a high temperature of 180 °C for 4 h, by approximately one-tenth of conventional FAU syntheses using an OSDA. In silico analysis, based on the results of solid-state 29Si magic-angle spinning nuclear magnetic resonance spectra, revealed that the obtained FAU had a biased Al distribution compared with previously reported FAUs. We also succeeded in the first synthesis of FAU with biased Al distribution using N,N- dimethyl- 3, 5- dimethylpiperidinium cations that acted as organic structure-directing agents just under high-temperature conditions.

Fluorescent Eu3+/Tb3+ Metal-Organic Frameworks for Ratiometric Temperature Sensing Regulated by Ligand Energy.

This work presents three series of Eu/Tb metal-organic frameworks (MOFs) containing benzophenone-4,4'-dicarboxylic acid (H2BPNDC), 4,4'-dicarboxydiphenyl ether (H2OBA), and terephthalic acid (H2BDC) as the ligands. Eu/Tb MOFs have the same structural features in that their 3D frameworks are simplified as 2,3,10-connected {42.6}2{46.618.819.102}{4}2 topological networks. The solid-state fluorescence spectra of three Eu/Tb MOF series are attributed to the combined emissions of 5D0 → 7FJ (J = 1-4) transitions in Eu3+ and 5D4 → 7FJ (J = 6-5) transitions in Tb3+. The nEu:nTb of Eu/Tb MOFs is optimized as 1:69 based on the relationships between ITb(545)/IEu(614) and nEu:nTb; that is, Eu0.0143Tb0.9857-L (L = BPNDC2-, OBA2-, and BDC2-) were selected to carry out the following temperature (T)-sensing tests. The fluorescence mechanism of Eu0.0143Tb0.9857-L can be explained by a ligand-to-metal charge transfer combined with an intermetallic Tb3+ → Eu3+ energy transfer. The T-dependent fluorescence indicates linear relationships with sensitivities of 1.85% K-1 for Eu0.0143Tb0.9857-BPNDC, 6.49% K-1 for Eu0.0143Tb0.9857-OBA, and 0.28% K-1 for Eu0.0143Tb0.9857-BDC. The influence of T on the lowest excited triplet energy levels (T1 values) of the ligands reveals that the ligand energy regulation impacts their fluorescence properties, including the sensitivity, fluorescence quenching rate, quantum yield, and fluorescence lifetime. This shows that Eu0.0143Tb0.9857-BPNDC is sufficiently sensitive to T, making it applicable in noncontact T measurements.

Impact of residual extractives on the thermal stability of softwood Kraft pulp

Wood extractives are known to cause problems during the production of pulp and paper and to impact their mechanical properties. In the present work, we systematically explored whether minute residual amounts of extractives that reprecipitate on the fiber surface in the final stages of the pulping process would lower the thermal resilience of softwood Kraft pulp. Pulp samples subjected to different extraction methods were characterized by means of thermogravimetric analysis. The compound classes constituting the respective extracts were identified and quantified via gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID) and the influence of the individual compound classes on the thermal stability of the samples was investigated separately. Soxhlet extraction with an ethanol/toluene solvent system clearly led to increased thermal stability. Besides fatty acids and resin acids also sterols and sterol esters that do not carry carboxylic acid functionalities contributed to the deterioration of the thermal pulp properties. Lateral order indices derived from Fourier transformed infrared spectra and crystallinity indices derived from solid-state 13C nuclear magnetic resonance spectra indicate that upon thermal degradation, the presence of even minute amounts of extractives leads to an increased degree of supramolecular disorder. Moreover, the characterization of the samples’ carbohydrate composition by means of acidic hydrolysis showed a tendency towards facilitated pyrolysis of the hemicelluloses if extractives were present in the pulp.

Investigation of the Geometric and Spectroscopic Properties of Four Twisted Triphenylpyridinium Donor-Acceptor Dyes.

The geometric and spectroscopic properties of four cationic N-aryl-2,4,6-triphenylpyridinium-based donor-acceptor dyes─1-[4-(9H-carbazol-9-yl)phenyl]-2,4,6-triphenylpyridinium, 1-[4-(N,N-diphenylamino)phenyl]-2,4,6-triphenylpyridinium, 1-(9-phenyl-9H-carbazol-3-yl)-2,4,6-triphenylpyridinium, and 1-(9-ethyl-9H-carbazol-3-yl)-2,4,6-triphenylpyridinium─are reported. The four dyes exhibited a twisted, quasi-perpendicular geometry about the central donor-acceptor bond, shown by X-ray crystallography and supported by Raman spectroscopy and DFT calculations. The electronic absorption spectra show weak charge transfer (CT) transitions at about 400 nm (ε ∼ 3000 L mol-1 cm-1). Time dependent (TD) DFT supported the nature of the CT transition, displaying an 89-97% shift in electron density from the donor to the acceptor upon electronic excitation. Excited state geometry calculations revealed significant geometry changes upon electronic excitation. Enhancement of vibrational modes attributable to this transition was also recognized in the resonance Raman spectra. Emission spectroscopies showed two distinct emission bands. The lower energy band, resulting from radiative decay of the CT excited state, exhibited large anomalous Stokes shifts of ∼9000 cm-1. Much of the Stokes shift was a consequence of geometry changes between the ground and excited states. This was confirmed by variable temperature emission studies, with Stokes shifts reducing by up to 3000 cm-1 upon cooling from 293 to 80 K. Additionally, a high energy aggregation induced emission band was present for two of the dyes, resulting from the inhibition of excited state geometry reorganization and supported by solid-state emission spectra. These phenomena exemplify the importance of geometry in short range donor-acceptor dyes such as these.

Electrochemical, Photophysical, Morphological and DFT Study of Polymorphic Sn(IV)-Porphyrins Containing Fluorinated Axial Ligand.

In this study, we report the polymorphism of six coordinated Sn(IV)- tetrabromophenyl porphyrins axially armed with fluorine-substituted phenolate ligands (structural formula [Sn(TBrPP)2+ (A- )2 ], where A is the axial ligand=3,5-difluoro phenol, compound 1). One form stabilizes in triclinic system (namely, 1α), and the other stabilizes in monoclinic system (namely, 1β). The two 1α and 1β polymorphs display distinct photophysical and morphological properties in the solid state. X-ray diffraction study reveals that these polymorphs 1α and 1β significantly differ in their supramolecular architecture, different axial phenolate conformations, and noncovalent interactions, which are responsible for their distinct solid-state properties. The crystal packing of these polymorphs dominates by intermolecular C-H⋅⋅⋅F, C-H⋅⋅⋅π and C-Br⋅⋅⋅F interhalogen interactions. Furthermore, the solid-state emission spectra of 1α showed red-shifted emission bands with respect to 1β, in addition the redox behavior of 1α is slightly different in comparison to 1β. Complementary theoretical studies with Hirshfeld surface analysis show the definite role of Br⋅⋅⋅F interhalogen interactions in the overall stability. Mapping the electrostatic potential isosurfaces with the aid of density functional theory in compound 1 clearly shows the presence of σ-hole, a requisite feature to show halogen interactions in the crystalline state. In addition, lattice energy and single point energy calculation shows that 1α was found to be energetically more favorable and thermodynamically more stable compare to 1β.