Pervaporation Separation and Catalysis Activity of Novel Zirconium Silicalite-1 Zeolite Membrane

Novel zirconium silicalite‐1 zeolite membrane was hydrothermally prepared on the mullite porous support at 150–185°C for 40–72 h by an "in situ" method using tetraethyl orthosilicate (TEOS), zirconium butoxide (ZBOT) and tetrapropylammonium hydroxide (TPAOH) as silica source, zirconium source and organic structure directing agent, respectively. X‐ray diffraction (XRD) patterns, fourier transformed infrared (FT‐IR) spectra, and inductively coupled plasma‐atomic emission spectrometry (ICP) of the accompanying zeolite powder confirmed that the zirconium was isomorphously incorporated into the zeolite framework. The surface chemical compositions of the obtained membrane were measured with an energy‐dispersive X‐ray spectral analyzer (EDS), and the membrane morphologies were observed by a scanning electron microscope (SEM). The results showed that the zeolite crystals growing on the support were zirconium silicalite‐1 zeolites, and the dense membrane layer was composed of the well inter‐growing zeolite crystals. The zirconium silicalite‐1 zeolite membrane, which was derived from the synthesis solution having a molar ratio of 1.00SiO₂:0.01ZrO₂:0.17TPAOH:120H₂O, showed high ethanol permselectivity with a flux of 1.01 kg/(m²·h) accompanied with a separation factor of 73 for ethanol/water (5/95, w/w) system under a pervaporation condition at 60°C. Moreover, this membrane displayed pervaporation‐aided catalysis activity for iso‐propanol oxidation with hydrogen peroxide as oxidant, and the corresponding iso‐propanol conversion was 35%.     

Controllably Confined ZnO on USY Zeolites (USY@ZnO/Al2O3) as Efficient Lewis Acid Catalysts for Baeyer–Villiger Oxidation

A ZnAl‐LDHs (layered double hydroxides) phase was readily formed on the surface of a USY zeolite through a distinctive in situ growth method that benefitted from the interaction of the added Zn source and aluminum species extracted from the Al‐rich USY zeolite crystals. The migration of aluminum and simultaneous interaction with the external Zn source took place in one pot to form a ZnAl‐LDHs phase coated on the surface of the USY crystals. Upon calcination, the ZnAl‐LDHs phase was transformed into a ZnO/Al₂O₃ composite that was still firmly anchored on the USY zeolite, without sacrificing the core–shell structure. The resultant USY@ZnO/Al₂O₃ materials gave rise to unique Lewis acidity and hierarchical porosity, which endowed the catalyst with promising performance in the Baeyer–Villiger oxidation of ketones with H₂O₂ or bulky tert‐butyl hydroxide as an oxidant.     

Hydrogen‐bonded structures and interaction energies in two forms of the SGLT‐2 inhibitor sotagliflozin

The sotagliflozin molecule exhibits two fundamentally different molecular conformations in form 1 {systematic name: (2S ,3R ,4R ,5S ,6R )‐2‐[4‐chloro‐3‐(4‐ethoxybenzyl)phenyl]‐6‐(methylsulfanyl)tetrahydro‐2H‐pyran‐3,4,5‐triol, C₂₁H₂₅ClO₅S, (I)} and the monohydrate [C₂₁H₂₅ClO₅S·H₂O, (II)]. Both crystals display hydrogen‐bonded layers formed by intermolecular interactions which involve the three –OH groups of the xyloside fragment of the molecule. The layer architectures of (I) and (II) contain a non‐hydrogen‐bonded molecule–molecule interaction along the short crystallographic axis (a axis) whose total PIXEL energy exceeds that of each hydrogen‐bonded molecule–molecule pair. The hydrogen‐bonded layer of (I) has the topology of the 4‐connected sql net and that formed by the water and sotagliflozin molecules of (II) has the topology of a 3,7‐connected net.     

Dual‐Mesoporous ZSM‐5 Zeolite with Highly b‐Axis‐Oriented Large Mesopore Channels for the Production of Benzoin Ethyl Ether

Dual‐mesoporous ZSM‐5 zeolite with highly b axis oriented large mesopores was synthesized by using nonionic copolymer F127 and cationic surfactant CTAB as co‐templates. The product contains two types of mesopores—smaller wormlike ones of 3.3 nm in size and highly oriented larger ones of 30–50 nm in diameter along the b axis—and both of them interpenetrate throughout the zeolite crystals and interconnect with zeolite microporosity. The dual‐mesoporous zeolite exhibits excellent catalytic performance in the condensation of benzaldehyde with ethanol and greater than 99 % selectivity for benzoin ethyl ether at room temperature, which can be ascribed to the zeolite lattice structure offering catalytically active sites and the hierarchical and oriented mesoporous structure providing fast access of reactants to these sites in the catalytic reaction. The excellent recyclability and high catalytic stability of the catalyst suggest prospective applications of such unique mesoporous zeolites in the chemical industry.     

New Light on an Old Story: The Crystal Structure of Boron Tetrathiophosphate Revisited

The crystal structure of boron tetrathiophosphate BPS₄ was reinvestigated using single‐crystal X‐ray diffraction. The structure shows unidimensional chains similar to SiS₂ as structural motifs. BPS₄ crystallizes in the orthorhombic space group Ibam (no. 72), with a = 5.6173(3), b = 8.9929(4), c = 5.2433(3) Å and V = 264.87(2) ų and is closely related to the orthorhombic high‐temperature modification of AlPS₄ (ht‐AlPS₄). The SiS₂‐like chains are all oriented parallel to the c axis, which explains the needle‐like morphology and that the crystals easily cleave to thinner needles under mechanical stress. While ht‐AlPS₄ shows an ordered Al‐P sublattice, the B‐P sublattice in BPS₄ is substantially disordered. The thermal properties of BPS₄ were investigated by DTA measurements and a detailed analysis of the Raman spectrum assisted by quantum mechanical calculations is presented. The crystallographic disorder in BPS₄ is the result of inter‐chain disorder, whereas local intra‐chain ordering of B and P can be concluded from Raman spectroscopy.     

Self‐Assembly Film of Zeolite Y Nanocrystals Loading Palladium on an Au Electrode for Electrochemical Applications

Nano‐scale zeolite Y crystals were synthesized, and palladium nanoparticles were prepared in the supercage of the zeolite by “ship‐in‐a‐bottle” approach. A novel method to fabricate zeolite‐modified electrode (ZME) loading Pd nanoparticles was developed, in which the zeolite Y loading Pd²⁺ ions was self‐assembled on (3‐mercaptopropyl) trimethoxysilane‐attached Au surface to form the stable and density packed multilayers (SAM‐ZME). The structures of zeolite Y and the SAM‐ZME were investigated by using TEM, XRD and SEM techniques. Pd²⁺ ions in the SAM‐ZME were converted into Pd nanoparticles (Pd_n⁰) by two steps consisting of the electrochemical reduction as well as the succeeding admission and release of CO. The redox couple [Fe(CN)₆]^3?/4? was used to probe the electron‐transfer barrier properties during self‐assembling process. Moreover, the special properties of the SAM‐ZME loading Pd_n⁰ were studied by using cyclic voltammetry and CO‐probe in situ FTIR spectroscopy. The results illustrated that Pd_n⁰ in the SAM‐ZME exhibits higher electrocatalytic activity for oxidation of adsorbed CO than that of ZME prepared in our previous study by zeolite coating method. The present study is of importance in design and preparation of SAM‐ZME, which poccesseses excellent properties for the immobilization of electrocatalysts or biomolecules.     

Channel‐forming solvates of 6‐chloro‐2,5‐dihydroxypyridine and its solvent‐free tautomer 6‐chloro‐5‐hydroxy‐2‐pyridone

On crystallization from CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂, 6‐chloro‐5‐hydroxy‐2‐pyridone, C₅H₄ClNO₂, (I), undergoes a tautomeric rearrangement to 6‐chloro‐2,5‐dihydroxypyridine, (II). The resulting crystals, viz. 6‐chloro‐2,5‐dihydroxypyridine chloroform 0.125‐solvate, C₅H₄ClNO₂·0.125CHCl₃, (IIa), 6‐chloro‐2,5‐dihydroxypyridine carbon tetrachloride 0.125‐solvate, C₅H₄ClNO₂.·0.125CCl₄, (IIb), 6‐chloro‐2,5‐dihydroxypyridine 1,2‐dichloroethane solvate, C₅H₄ClNO₂·C₂H₄Cl₂, (IIc), and 6‐chloro‐2,5‐dihydroxypyridine 1,1,2,2‐tetrachloroethane solvate, C₅H₄ClNO₂·C₂H₂Cl₄, (IId), have I4₁/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent‐free crystals with P2₁/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion‐related molecules form R²₂(8) dimers via pairs of N—H...O hydrogen bonds. The dimers are linked by O—H...O hydrogen bonds into R⁴₆(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel‐containing pyridine solvate crystals, viz. (IIa)–(IId), two independent host molecules form an R²₂(8) dimer via a pair of O—H...N hydrogen bonds. One molecule is further linked by O—H...O hydrogen bonds to two 4₁ screw‐related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O—H...O hydrogen bonded to two related equivalents to form tetrameric R⁴₄(28) rings. The dimers are π–π stacked with inversion‐related dimers, which in turn stack the R⁴₄(28) rings along c to form continuous solvent‐accessible channels. CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂ solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels.     

Crystal Growth and Structure Refinement of K4Ge9

Deep‐red moisture and air sensitive single crystals of K₄Ge₉ were obtained by reacting GeO₂ and elemental Ge with metallic W and K at high temperature in a niobium ampoule. The crystal structure of the compound was determined by single crystal X‐ray diffraction experiments. K₄Ge₉ crystallizes in a polar space group R3c (No. 161), Z = 4 with a = 21.208(1) and c = 25.096(2) Å. The compound contains discrete Ge₉^4? Wade's nido‐clusters which are packed according to a hierarchical atom‐to‐cluster replacement of the Cr₃Si prototype and are separated by K⁺ cations. Two independent [Ge₉]^4? clusters A (at Cr positions) and B (at Si positions) are found with a ratio A:B = 3:1. The B ‐type cluster satisfactorily represents orientational disorder around the three‐fold axis.     

B‐MWW Zeolite: The Case Against Single‐Site Catalysis

Boron‐containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron‐containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B₂(OH)_xO_(3?x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM‐22 isomorphously substituted with boron (B‐MWW). Using ¹¹B solid‐state NMR spectroscopy, we show that the majority of boron species in B‐MWW exist as isolated BO₃ units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B‐MWW for ODH of propane falsifies the hypothesis that site‐isolated BO₃ units are the active site in boron‐based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium‐based catalysts and provides an important piece of the mechanistic puzzle.     

Decoupled Spin Crossover and Structural Phase Transition in a Molecular Iron(II) Complex

Crystalline [Fe(bppSMe)₂][BF₄]₂ ( 1 ; bppSMe=4‐(methylsulfanyl)‐2,6‐di(pyrazol‐1‐yl)pyridine) undergoes an abrupt spin‐crossover (SCO) event at 265±5 K. The crystals also undergo a separate phase transition near 205 K, involving a contraction of the unit‐cell a axis to one‐third of its original value (high‐temperature phase 1; Pbcn, Z=12; low‐temperature phase 2; Pbcn, Z=4). The SCO‐active phase 1 contains two unique molecular environments, one of which appears to undergo SCO more gradually than the other. In contrast, powder samples of 1 retain phase 1 between 140–300 K, although their SCO behaviour is essentially identical to the single crystals. The compounds [Fe(bppBr)₂][BF₄]₂ ( 2 ; bppBr=4‐bromo‐2,6‐di(pyrazol‐1‐yl)pyridine) and [Fe(bppI)₂][BF₄]₂ ( 3 ; bppI=4‐iodo‐2,6‐di(pyrazol‐1‐yl)‐pyridine) exhibit more gradual SCO near room temperature, and adopt phase 2 in both spin states. Comparison of 1 – 3 reveals that the more cooperative spin transition in 1 , and its separate crystallographic phase transition, can both be attributed to an intermolecular steric interaction involving the methylsulfanyl substituents. All three compounds exhibit the light‐induced excited‐spin‐state trapping (LIESST) effect with T(LIESST=70–80 K), but show complicated LIESST relaxation kinetics involving both weakly cooperative (exponential) and strongly cooperative (sigmoidal) components.     

Antidiarrhetic loperamide hydrochloride

Single crystals of the anhydrous form of the title compound {systematic name: 1‐[3‐(dimethylcarbamoyl)‐3,3‐diphenylpropyl]‐4‐hydroxy‐4‐(4‐chlorophenyl)piperidin‐1‐ium chloride}, C₂₉H₃₄ClN₂O₂⁺·Cl⁻, were obtained by diffusion of acetone into a solution in 2‐propanol. In the structure, N—H...Cl⁻ and O—H...Cl⁻ hydrogen bonds connect neighbouring molecules and chloride anions to form chains along the c‐axis direction. Neighbouring chains along the b‐axis direction are connected by intermolecular C—H...Cl⁻ contacts, defining layers parallel to the (100) planes. The layers are connected by weak intermolecular C—H...Cl interactions only, which may account for the plate‐like shape of the crystals.     

Jahn‐Teller‐Ordnung in Mangan(III)‐fluoridsulfaten. II. Phasenübergang und Verzwillingung bei K2[MnF3(SO4)] und 1D Magnetismus in Verbindungen A2[MnF3(SO4)] (A = K,NH4, Rb,Cs)

Jahn‐Teller Ordering in Manganese(III) Fluoride Sulfates. II. Phase Transition and Twinning of K₂[MnF₃(SO₄)] and 1D Magnetism in Compounds A₂[MnF₃(SO₄)] (A = K, NH₄, Rb, Cs) According to single‐crystal X‐ray investigations, K₂[MnF₃(SO₄)] crystallizes at low temperature, like the isostructural Rb, NH₄, and Cs analogues in space group P2₁/c, Z = 4, e.g. at 100 K with a = 7.197, b = 10.704, c = 8.427Å, β = 91.84°. Below about 300 K, the crystals are found to be [001] axis twins. Using a new integration method for area detector records, nearly complete intensity data could be gained allowing for structure refinements of similar quality as for untwinned crystals (e.g. at 100 K: wR₂ = 0.050, R = 0.020 for all reflections). With rising temperature, the monoclinic angle approaches continuously 90°. For an ordering parameter Δβ = β?90° a 2^nd‐order phase transition is observed with an exponent λ = 0.17. At the transition temperature of 280 K resulting from the fit, the monoclinic structure changes – with delay – to orthorhombic with the minimum super‐group Pnca, a = 7.243, b = 10.763, c = 8.457Å, R = 0.024, as found in an early structure determination at room temperature by Edwards 1971. In the chain‐like [MnF₃(SO₄)]^2? anions, manganese(III) is octahedrally coordinated by two trans‐terminal and two trans‐bridging fluorine ligands as well as by the O atoms of two trans‐bridging sulfate ligands. At low temperature, the octahedral elongation by the Jahn‐Teller effect alternates between a F–Mn–F and an O–Mn–O axis (antiferrodistortive ordering). All bridges are asymmetric. From about 320 K on they become symmetric. Due to 2D dynamical Jahn‐Teller effect all octahedra appear compressed. All compounds A₂[MnF₃(SO₄)] show 1D antiferromagnetism. The antiferrodistortive Jahn‐Teller order at low temperatures and the small bridge angles explain the much lower magnetic exchange energies and their inverse relation to the bridge angles as compared with other fluoromanganate(III) chain compounds with the usual ferrodistortive ordering.     

Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion

Gel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (T_m). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the T_m. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization P_r of 100 mC/m² and electromechanical coupling factor along the thickness direction k_t of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001     

Zwei Dodekahydro‐closo‐Dodekaborate mit Lone‐Pair‐Kationen der 6. Periode im Vergleich: Tl2[B12H12] und Pb(H2O)3[B12H12]·3H2O

During the reaction of an aqueous solution of (H₃O)₂[B₁₂H₁₂] with Tl₂CO₃ anhydrous thallium(I) dodecahydro‐closo‐dodecaborate Tl₂[B₁₂H₁₂] is obtained as colorless, spherical single crystals. It crystallizes in the cubic system with the centrosymmetric space group Fm$\bar{3}$ (a = 1074.23(8) pm, Z = 4) in an anti‐CaF₂ type structure. Four quasi‐icosahedral [B₁₂H₁₂]^2– anions (d(B–B) = 180–181 pm, d(B–H) = 111 pm) exhibit coordinative influence on each Tl⁺ cation and provide a twelvefold coordination in the shape of a cuboctahedron (d(Tl–H) = 296 pm). There is no observable stereochemical activity of the non‐bonding electron pairs (6s² lone pairs) at the Tl⁺ cations. By neutralization of an aqueous solution of the acid (H₃O)₂[B₁₂H₁₂] with PbCO₃ and after isothermic evaporation colorless, plate‐like single crystals of lead(II) dodecahydro‐closo‐dodecaborate hexahydrate Pb(H₂O)₃[B₁₂H₁₂] · 3H₂O can be isolated. This compound crystallizes orthorhombically with the non‐centrosymmetric space group Pna2₁ (a = 1839.08(9), b = 1166.52(6), c = 717.27(4) pm, Z = 4). The crystal structure of Pb(H₂O)₃[B₁₂H₁₂] · 3H₂O is characterized as a layer‐like arrangement. The Pb²⁺ cations are coordinated in first sphere by only three oxygen atoms from water molecules (d(Pb–O) = 247–248 pm). But a coordinative influence of the [B₁₂H₁₂]^2– anions (d(B–B) = 173–181 pm, d(B–H) = 93–122 pm) on lead has to be stated, too, as three hydrogen atoms from three different hydroborate anions are attached to the Pb²⁺ cations (d(Pb–H) = 258–270 pm) completing their first‐sphere coordination number to six. These three oxygen and three hydrogen ligands are arranged as quite irregular polyhedron leaving enough space for a stereochemical lone‐pair activity (6sp) at each Pb²⁺ cation. Since additional intercalating water of hydration is present as well, both classical H–O^δ– ··· ^+δH–O‐ and unconventional B–H^δ– ··· ^+δH–O hydrogen bonds play a significant role in the stabilization of the entire crystal structure.     

Synthesis of Zeolite ZSM-2 Using Zeolite NaX as Seeds

Introduction Oxygen and nitrogen have been produced tradition-ally by cryogenic distillation of air. Methods for the non-cryogenic separation based on selective adsorption have been developed and commercialized since the 1970s and have led to a cost-effective process for this important separation.1 Low-silica zeolites are important materials for producing oxygen by selective adsorption of nitrogen. In 19891990, a new generation of lith-ium-based adsorbents was developed.2,3 Highly lithium exc…     

Fabrication of b‐Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride

The fabrication of MFI zeolite films with particular b‐axis orientation is especially fascinating. Unlike the conventional alkaline or hydrofluoric acid (HF) assisted neutral synthesis route, here we develop a novel neutral synthesis solution system of TPABr/fumed silica/H₂O without the use of HF and successfully synthesize highly b‐oriented MFI zeolite films on glass‐plate substrates by secondary growth. The localized weak alkaline environment created by the dissolved Na₂O species from the substrate is identified as the key factor for the depolymerization of fumed silica and subsequently the in‐plane growth of zeolite seed layers. Continuous b‐oriented MFI films can also be synthesized on other substrates in the presence of a glass plate or a trace amount of NaOH, which making our neutral synthesis route promising for the direct synthesis of MFI zeolite films and membranes on various substrates.     

Kinetics of Sorption,Desorption, and Diffusion in Zeolites

Sorption and desorption in zeolites (molecular sieves) have to be considered as complex processes, involving simultaneous diffusion in zeolite crystals, mass transfer in the intercrystalline void of a pellet, and heat transfer between the zeolitic sorbent and its surroundings. The kinetics of sorption and desorption, respectively, of n-C₄H₁₀ in zeolite X and of CO₂ in zeolite A have been investigated: only the initial rates of uptake or release of the sorbet are controlled by mass transfer alone whereas ultimately they also depend on the rate of heat transfer from the sorbent to its surroundings or vice versa. Diffusivities of the sorbate in the zeolite crystals can be obtained from the kinetics of mass transfer, provided the resistance due to viscous or Knudsen flow between the crystals of the zeolitic sorbent can be eliminated. A sample consisting of a monolayer of single crystals had to be used for this purpose in the n-butane/zeolite X system; the intracrystalline diffusivity obtained in this way is not in conflict with data obtained by NMR spectroscopy. The intracrystalline diffusivities obtained in this way—taking into account the coupling of several processes during sorption — are higher than values reported in the literature.     

Vaulted trans‐Bis(salicylaldiminato)platinum(II) Crystals: Heat‐Resistant,Chromatically Sensitive Platforms for Solid‐State Phosphorescence at Ambient Temperature

The synthesis, structure, and solid‐state emission of vaulted trans‐bis(salicylaldiminato)platinum(II) complexes are described. A series of polymethylene ( 1 : n=8; 2 : n=9; 3 : n=10; 4 : n=11; 5 : n=12; 6 : n=13) and polyoxyethylene ( 7 : m=2; 8 : m=3; 9 : m=4) vaulted complexes (R=H ( a ), 3‐MeO ( b ), 4‐MeO ( c ), 5‐MeO ( d ), 6‐MeO ( e ), 4‐CF₃O ( f ), 5‐CF₃O ( g )) was prepared by treating [PtCl₂(CH₃CN)₂] with the corresponding N,N′‐bis(salicylidene)‐1,ω‐alkanediamines. The trans coordination, vaulted structures, and the crystal packing of 1 – 9 have been unequivocally established from X‐ray diffraction studies. Unpredictable, structure‐dependent phosphorescent emission has been observed for crystals of the complexes under UV excitation at ambient temperature, whereas these complexes are entirely nonemissive in the solution state under the same conditions. The long‐linked complex crystals 4 – 6 , 8 , and 9 exhibit intense emission (Φ_77K=0.22–0.88) at 77 K, whereas short‐linked complexes 1 – 3 and 7 are non‐ or slightly emissive at the same temperature (Φ_77K<0.01–0.18). At 298 K, some of the long‐linked crystals, 4 a , 4 b , 5 c , 5 e , 6 c , 6 e , and 9 b , completely lose their high‐emission properties with elevation of the temperature (Φ_298K<0.01–0.02), whereas the other long‐linked crystals, 5 a , 6 a , 9 a , and 9 d , exhibit high heat resistance towards emission decay with increasing temperature (Φ_298K=0.21–0.38). Chromogenic control of solid‐state emission over the range of 98 nm can be performed simply by introducing MeO groups at different positions on the aromatic rings. Orange, yellow‐green, red, and yellow emissions are observed in the glass and crystalline state upon 3‐, 4‐, 5‐, and 6‐MeO substitution, respectively, whereas those with CF₃O substituents have orange emission, irrespective of the substitution position. DFT calculations (B3LYP/6‐31G*, LanL2DZ) showed that such chromatic variation is ascribed to the position‐specific influence of the substituents on the highest‐occupied molecular orbital (HOMO) and lowest‐unoccupied molecular orbital (LUMO) levels of the trans‐bis(salicylaldiminato)platinum(II) platform. The solid‐state emission and its heat resistance have been discussed on the basis of X‐ray diffraction studies. The planarity of the trans‐coordination sites is strongly correlated to the solid‐state emission intensities of crystals 1 – 9 at lower temperatures. The specific heat‐resistance properties shown exclusively by the 5 a , 6 a , 9 a , and 9 d crystals are due to their strong three‐dimensional hydrogen‐bonding interactions and/or Pt???Pt contacts, whereas heat‐quenchable crystals 4 a , 4 b , 5 c , 5 e , 6 c , 6 e , and 9 b are poorly bound with limited interactions, such as non‐, one‐, or two‐dimensional hydrogen‐bonding networks. These results lead to the conclusion that Pt???Pt contacts are an important factor in the heat resistance of solid‐state phosphorescence at ambient temperature, although the role of Pt???Pt contacts can be substituted by only higher‐ordered hydrogen‐bonding fixation.     

Twist‐chair conformation of the tetraoxepane ring remains unchanged in tetraoxaspirododecane diamines

A detailed structural analysis has been performed for N,N′‐bis(4‐chlorophenyl)‐7,8,11,12‐tetraoxaspiro[5.6]dodecane‐9,10‐diamine, C₂₀H₂₂Cl₂N₂O₄, (I), N,N′‐bis(2‐fluorophenyl)‐7,8,11,12‐tetraoxaspiro[5.6]dodecane‐9,10‐diamine, C₂₀H₂₂F₂N₂O₄, (II), and N,N′‐bis(4‐fluorophenyl)‐7,8,11,12‐tetraoxaspiro[5.6]dodecane‐9,10‐diamine, C₂₀H₂₂F₂N₂O₄, (III). The seven‐membered ring with two peroxide groups adopts a twist‐chair conformation in all three compounds. The lengths of the C—N and O—O bonds are slightly shorter than the average statistical values found in the literature for azepanes and 1,2,4,5‐tetraoxepanes. The geometry analysis of compounds (I)–(III), the topological analysis of the electron density at the (3, ?1) bond critical points within Bader's quantum theory of `Atoms in molecules' (QTAIM) and NBO (natural bond orbital) analysis at the B3LYP/6‐31G(d,2p) level of theory showed that there are n_O→σ*(C—O), n_N→σ*(C—O) and n_O→σ*(C—N) stereoelectronic effects. The molecules of compounds (I) and (III) are packed in the crystals as zigzag chains due to strong N—H…O and C—H…O hydrogen‐bond interactions, whereas the molecules of compound (II) form chains in the crystals bound by N—H…O, C—H…π and C—H…O contacts. All these data show that halogen atoms and their positions have a minimal effect on the geometric parameters, stereoelectronic effects and crystal packing of compounds (I)–(III), so that the twist‐chair conformation of the tetraoxepane ring remains unchanged.     

LiBC3: a new borocarbide based on graphene and heterographene networks

Li–B–C alloys have attracted much interest because of their potential use in lithium‐ion batteries and superconducting materials. The formation of the new compound LiBC₃ [lithium boron tricarbide; own structure type, space group P m 2, a = 2.5408 (3) Å and c = 7.5989 (9) Å] has been revealed and belongs to the graphite‐like structure family. The crystal structure of LiBC₃ presents hexagonal graphene carbon networks, lithium layers and heterographene B/C networks, alternating sequentially along the c axis. According to electronic structure calculations using the tight‐binding linear muffin‐tin orbital‐atomic spheres approximations (TB–LMTO–ASA) method, strong covalent B—C and C—C interactions are established. The coordination polyhedra for the B and C atoms are trigonal prisms and for the Li atoms are hexagonal prisms.