Luminescence Properties of C‐Diazaborolyl‐ortho‐Carboranes as Donor–Acceptor Systems

Seven derivatives of 1,2‐dicarbadodecaborane (ortho‐carborane, 1,2‐C₂B₁₀H₁₂) with a 1,3‐diethyl‐ or 1,3‐diphenyl‐1,3,2‐benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low‐energy fluorescence emissions with large Stokes shifts of 15100–20260 cm^?1 and quantum yields (Φ_F) of up to 65 % in the solid state. The low‐energy fluorescence emission, which was assigned to a charge‐transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C? C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660–18090 cm^?1 for the CT bands and 1960–5540 cm^?1 for the high‐energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ_F values between 8–32 %. Two distinct excited singlet‐state (S₁) geometries, denoted S₁(LE) and S₁(CT), were observed computationally for the benzodiazaborolyl‐ortho‐carboranes, the population of which depended on their orientation (ψ). TD‐DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C‐diazaborolyl‐ortho‐carboranes were viewed as donor–acceptor systems with the diazaborolyl group as the donor and the ortho‐carboranyl group as the acceptor.     

Thermodynamics of Carbon Dioxide Adsorption on the Protonic Zeolite H‐ZSM‐5

Adsorption of carbon dioxide on H‐ZSM‐5 zeolite (Si:Al=11.5:1) was studied by means of variable‐temperature FT‐IR spectroscopy, in the temperature range of 310–365 K. The adsorbed CO₂ molecules interact with the zeolite Brønsted‐acid OH groups bringing about a characteristic red‐shift of the O? H stretching band from 3610 cm^?1 to 3480 cm^?1. Simultaneously, the ν₃ mode of adsorbed CO₂ is observed at 2345 cm^?1. From the variation of integrated intensity of the IR absorption bands at both 3610 and 2345 cm^?1, upon changing temperature (and CO₂ equilibrium pressure), the standard adsorption enthalpy of CO₂ on H‐ZSM‐5 is ΔH⁰=?31.2(±1) kJ mol^?1 and the corresponding entropy change is ΔS⁰=?140(±10) J mol^?1 K^?1. These results are discussed in the context of available data for carbon dioxide adsorption on other protonic, and also alkali‐metal exchanged, zeolites.     

Wolves in Sheep's Clothing: μ‐Oxo‐Diiron Corroles Revisited

For well over 20 years, μ‐oxo‐diiron corroles, first reported by Vogel and co‐workers in the form of μ‐oxo‐bis[(octaethylcorrolato)iron] (Mössbauer δ 0.02 mm s^?1, ΔE_Q 2.35 mm s^?1), have been thought of as comprising a pair antiferromagnetically coupled low‐spin Fe^IV centers. The remarkable stability of these complexes, which can be handled at room temperature and crystallographically analyzed, present a sharp contrast to the fleeting nature of enzymatic, iron(IV)‐oxo intermediates. An array of experimental and theoretical methods have now shown that the iron centers in these complexes are not Fe^IV but intermediate‐spin Fe^III coupled to a corrole^.2?. The intramolecular spin couplings in {Fe[TPC]}₂(μ‐O) were analyzed via DFT(B3LYP) calculations in terms of the Heisenberg–Dirac–van Vleck spin Hamiltonian H=J_Fe–corrole(S_Fe?S_corrole)+J_Fe–Fe′(S_Fe?S_Fe′)+J_{Fe′–corrole}(S_Fe′?S_corrole′), which yielded J_Fe–corrole=J_{Fe′–corrole′}=0.355 eV (2860 cm^?1) and J_Fe–Fe′=0.068 eV (548 cm^?1). The unexpected stability of μ‐oxo‐diiron corroles thus appears to be attributable to charge delocalization via ligand noninnocence.     

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Kinetic measurements for the thermal rearrangement of 2,2‐diphenyl‐1‐[(E)‐styryl]cyclopropane ( 22a ) to 3,4,4‐triphenylcyclopent‐1‐ene ( 23a ) in decalin furnished ΔH =31.0±1.2 kcal mol^?1 and ΔS =?6.0±2.6 e.u. The lowering of ΔH^≠ by 20 kcal mol^?1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (+)‐(S)‐ 22a proceeds with ΔH =28.2±0.8 kcal mol^?1 and ΔS =?5±2 e.u., and is at 150° 106 times faster than the rearrangement. Seven further 1‐(2‐arylethenyl)‐2,2‐diphenylcyclopropanes 22 , (E)‐ and (Z)‐isomers, were synthesized and characterized. The (E)‐compounds showed only modest substituent influence in their k_rac (at 119.4°) and k_isom (at 159.3°) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log k_rac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring‐opening of the preponderant s‐trans‐conformation of 22 gives rise to the 1‐exo‐phenylallyl radical 26 that bears the diphenylethyl radical in 3‐exo‐position, and is responsible for racemization. The 1‐exo‐3‐endo‐substituted allylic diradical 27 arises from the minor s‐gauche‐conformation of 22 and is capable of closing the three‐ or the five‐membered ring, 22 or 23 , respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum‐chemical calculations by Houk et al. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate?     

Dynamic Open Coordination Cage from Nonsymmetrical Imidazole–Pyridine Ditopic Ligands for Turn‐On/Off Anion Binding

This work demonstrates a new nonconventional ligand design, imidazole/pyridine‐based nonsymmetrical ditopic ligands ( 1 and 1 ^S ), to construct a dynamic open coordination cage from nonsymmetrical building blocks. Upon complex formation with Pd²⁺ at a 1:4 molar ratio, 1 and 1 ^S initially form mononuclear PdL₄ complexes (Pd²⁺( 1 )₄ and Pd²⁺( 1 ^S )₄) without formation of a cage. The PdL₄ complexes undergo a stoichiometrically controlled structural transition to Pd₂L₄ open cages ((Pd²⁺)₂( 1 )₄ and (Pd²⁺)₂( 1 ^S )₄) capable of anion binding, leading to turn‐on anion binding. The structural transitions between the Pd₂L₄ open cage and the PdL₄ complex are reversible. Thus, stoichiometric addition (2 equiv) of free 1 ^S to the (Pd²⁺)₂( 1 ^S )₄ open cage holding a guest anion ((Pd²⁺)₂( 1 ^S )₄?G^?) enables the structural transition to the Pd²⁺( 1 ^S )₄ complex, which does not have a cage and thus causes the release of the guest anion (Pd²⁺( 1 ^S )₄+G^?).     

Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex

The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF₆)₂ (bztpen=N‐benzyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethylenediamine) displays an S=1/2?S=3/2 spin crossover (SCO) behavior (T_1/2=370 K, ΔH=12.48 kJ mol^?1, ΔS=33 J K^?1 mol^?1) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0?S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120–420 K affording a detailed picture of how the electronic distribution of the t_2g–e_g orbitals modulates the structure of the {FeNO}⁷ bond, providing valuable magneto–structural and spectroscopic correlations and DFT analysis.     

Ferromagnetic Interactions in a 1D Alternating Linear Chain of π‐Stacked 1,3‐Diphenyl‐7‐(thien‐2‐yl)‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl Radicals

X‐ray studies show that 1,3‐diphenyl‐7‐(thien‐2‐yl)‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl ( 6 ) adopts a distorted, slipped π‐stacked structure of centrosymmetric dimers with alternate short and long interplanar distances (3.48 and 3.52 Å). Cyclic voltammograms of 7‐(thien‐2‐yl)benzotriazin‐4‐yl 6 show two fully reversible waves that correspond to the ?1/0 and 0/+1 processes. EPR and DFT studies on radical 6 indicate that the spin density is mainly delocalized over the triazinyl fragment. Magnetic susceptibility measurements show that radical 6 obeys Curie–Weiss behavior in the 5–300 K region with C=0.378 emu K mol^?1 and θ=+4.72 K, which is consistent with ferromagnetic interactions between S=1/2 radicals. Fitting the magnetic susceptibility revealed the behavior is consistent with an alternating ferromagnetic chain (g=2.0071, J₁=+7.12 cm^?1, J₂=+1.28 cm^?1).     

Pressure effects on cation migration in 2,5‐di‐tert‐butyl‐1,4‐benzoquinone radical anion

Pressure effects on the two‐site jumping of sodium and potassium cations in a 2,5‐di‐tert‐butyl‐1,4‐benzoquinone ion pair have been studied using a high‐pressure EPR technique. The rate constants of the intramolecular and intermolecular migrations for Na⁺ and K⁺ were determined from an EPR spectral simulation. The migration rates were found to be accelerated by increasing the external pressure. Using the pressure dependence of the migration rates, we estimated the activation volumes of the intramolecular (ΔV₁^?) and intermolecular (ΔV₂^?) processes for the Na⁺ and K⁺ migrations: ΔV₁^? = ?5.3 cm³ mol^?1 and ΔV₂^? = ?29 cm³ mol^?1 for Na⁺, and ΔV₁^? = ?8.3 cm³ mol^?1 and ΔV₂^? = ?0.85 cm³ mol^?1 for K⁺. Based on the results, the mechanisms for the two‐site jumping of Na⁺ and K⁺ are discussed in terms of volume. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 397–401, 2001     

Evidence for a Rapid Degenerate Hetero‐Cope‐Type Rearrangement in [Cp*W(S)2S‐CH2‐CHCH2]

Treatment of the salt [PPh₄]⁺[Cp*W(S)₃]^? ( 6 ) with allyl bromide gave the neutral complex [Cp*W(S)₂S‐CH₂‐CH?CH₂] ( 7 ). The product 7 was characterized by an X‐ray crystal structure analysis. Complex 7 features dynamic NMR spectra that indicate a rapid allyl automerization process. From the analysis of the temperature‐dependent NMR spectra a Gibbs activation energy of ΔG^≠ (278 K)≈13.7±0.1 kcal mol^?1 was obtained [ΔH^≠≈10.4±0.1 kcal mol^?1; ΔS^≠≈?11.4 cal mol^?1 K^?1]. The DFT calculation identified an energetically unfavorable four‐membered transition state of the “forbidden” reaction and a favorable six‐membered transition state of the “Cope‐type” allyl rearrangement process at this transition‐metal complex core.     

Kinetics and mechanism of the interaction of adenosine with cis‐diaqua(cis‐1,2‐diaminocyclohexane)platinum(II) perchlorate in aqueous medium

The kinetics of the interaction of adenosine with cis‐[Pt(cis‐dach)(OH₂)₂]²⁺ (dach = diaminocyclohexane) was studied spectrophotometrically as a function of [cis‐[Pt(cis‐dach)(OH₂)₂]²⁺], [adenosine], and temperature at a particular pH (4.0), where the substrate complex exists predominantly as the diaqua species and the ligand adenosine exists as a neutral molecule. The substitution reaction shows two consecutive steps: the first is the ligand‐assisted anation followed by a chelation step. The activation parameters for both the steps have been evaluated using Eyring equation. The low negative value of ΔH^≠₁ (43.1 ± 1.3 kJ mol^?1) and the large negative value of ΔS^≠₁ (?177 ± 4 J K^?1 mol^?1) along with ΔH^≠₂ (47.9 ± 1.8 kJ mol^?1) and ΔS^≠₂ (?181 ± 6 J K^?1 mol^?1) indicate an associative mode of activation for both the aqua ligand substitution processes. The kinetic study was substantiated by infrared and electrospray ionization mass spectroscopic analysis. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 219–229, 2011     

Effect of Inter‐Porphyrin Distance on Spin‐State in Diiron(III) μ‐Hydroxo Bisporphyrins

The synthesis, structure, and properties of bischloro, μ‐oxo, and a family of μ‐hydroxo complexes (with BF₄^?, SbF₆^?, and PF₆^? counteranions) of diethylpyrrole‐bridged diiron(III) bisporphyrins are reported. Spectroscopic characterization has revealed that the iron centers of the bischloro and μ‐oxo complexes are in the high‐spin state (S=⁵/₂). However, the two iron centers in the diiron(III) μ‐hydroxo complexes are equivalent with high spin (S=⁵/₂) in the solid state and an intermediate‐spin state (S=³/₂) in solution. The molecules have been compared with previously known diiron(III) μ‐hydroxo complexes of ethane‐bridged bisporphyrin, in which two different spin states of iron were stabilized under the influence of counteranions. The dimanganese(III) analogues were also synthesized and spectroscopically characterized. A comparison of the X‐ray structural parameters between diethylpyrrole and ethane‐bridged μ‐hydroxo bisporphyrins suggest an increased separation, and hence, less interactions between the two heme units of the former. As a result, unlike the ethane‐bridged μ‐hydroxo complex, both iron centers become equivalent in the diethylpyrrole‐bridged complex and their spin state remains unresponsive to the change in counteranion. The iron(III) centers of the diethylpyrrole‐bridged diiron(III) μ‐oxo bisporphyrin undergo very strong antiferromagnetic interactions (J=?137.7 cm^?1), although the coupling constant is reduced to only a weak value in the μ‐hydroxo complexes (J=?42.2, ?44.1, and ?42.4 cm^?1 for the BF₄, SbF₆, and PF₆ complexes, respectively).     

3,4‐Phenylenedioxythiophene (PheDOT) Based Hole‐Transporting Materials for Perovskite Solar Cells

Two new electron‐rich molecules based on 3,4‐phenylenedioxythiophene (PheDOT) were synthesized and successfully adopted as hole‐transporting materials (HTMs) in perovskite solar cells (PSCs). X‐ray diffraction, absorption spectra, photoluminescence spectra, electrochemical properties, thermal stabilities, hole mobilities, conductivities, and photovoltaic parameters of PSCs based on these two HTMs were compared with each other. By introducing methoxy substituents into the main skeleton, the energy levels of PheDOT‐core HTM were tuned to match with the perovskite, and its hole mobility was also improved (1.33×10^?4 cm² V^?1 s^?1, being higher than that of spiro‐OMeTAD, 2.34×10^?5 cm² V^?1 s^?1). The PSC based on MeO‐PheDOT as HTM exhibits a short‐circuit current density (J_sc) of 18.31 mA cm^?2, an open‐circuit potential (V_oc) of 0.914 V, and a fill factor (FF) of 0.636, yielding an encouraging power conversion efficiency (PCE) of 10.64 % under AM 1.5G illumination. These results give some insight into how the molecular structures of HTMs affect their performances and pave the way for developing high‐efficiency and low‐cost HTMs for PSCs.     

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

The dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) ( 3 ) and lithium‐benzo[b]fluorenide(tmeda) ( 4 ) using CP/MAS solid‐state ¹³C‐ and ¹⁵N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the ¹³C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH^?=42.7 kJ mol^?1, ΔS^?=?5.3 J mol^?1 K^?1, and =44.3 kJ mol^?1 for 3 , and ΔH^?=36.8 kJ mol^?1, ΔS^?=?17.7 J mol^?1 K^?1, and =42.1 kJ mol^?1 for 4 , respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T_1ρ, the ¹³C spin‐lattice relaxation time in the rotating frame, and led to ΔH^?=24.8 kJ mol^?1, ΔS^?=?49.2 J mol^?1 K^?1, and =39.5 kJ mol^?1 for 3 , and ΔH^?=18.2 kJ mol^?1, ΔS^?=?65.3 J mol^?1 K^?1, and =37.7 kJ mol^?1 for 4 , respectively. For (D₁₂)‐ 3 , the rotation of the CD₃ groups has also been studied, and a barrier E_a of 14.1 kJ mol^?1 was found.     

Gem‐dinitromethyl‐substituted Energetic Metal–Organic Framework based on 1,2,3‐Triazole from in situ Controllable Synthesis

Synthesizing energetic metal–organic frameworks at ambient temperature and pressure has been always a challenge in the research area of energetic materials. In this work, through in situ controllable synthesis, energetic metal–organic framework gem‐dinitromethyl‐substituted dipotassium 4,5‐bis(dinitromethyl)‐1,2,3‐triazole with a “cage‐like” crystal packing was obtained and characterized. Most importantly, for the first time, we found that it could be successfully afforded with a catalytic effect of trifluoroacetic acid. This new compound exhibited its high density (2.04 g cm^?3) at ambient temperature, superior detonation velocity (8715 m s^?1) to that of lead azide (5877 m s^?1) and comparable to that of RDX (8748 m s^?1). Its detonation products are mainly N₂ (48.1 %), suggesting it is also a green energetic material. The above‐mentioned performance indicates its potential applications in detonator devices as lead‐free primary explosive.     

The First Fully Planar C5‐Conformation of Homooligopeptides Prepared from a Chiral α‐Ethylated α,α‐Disubstituted Amino Acid: (S)‐Butylethylglycine (=(2S)‐2‐Amino‐2‐ethylhexanoic Acid)

An optically active α‐ethylated α,α‐disubstituted amino acid, (S)‐butylethylglycine (=(2S)‐2‐amino‐2‐ethylhexanoic acid; (S)‐Beg; (S)‐ 2 ), was prepared starting from butyl ethyl ketone ( 1 ) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)‐Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C‐terminus, and a trifluoroacetyl group was used for the N‐terminus of the peptides. The structures of tri‐ and tetrapeptides 5 and 6 in the solid state were solved by X‐ray crystallographic analysis, and were shown to have a bent planar C₅‐conformation (tripeptide) and a fully planar C₅‐conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and ¹H‐NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl₃ solution was also a fully planar C₅‐conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α‐ethylated α,α‐disubstituted amino acid is a planar C₅‐conformation.     

Controlling Helical Chirality in Atrane Structures: Solvent‐Dependent Chirality Sense in Hemicryptophane‐Oxidovanadium(V) Complexes

The diastereomeric hemicryptophane oxidovanadium(V) complexes (P)‐(S,S,S)‐ 3 and (M)‐(S,S,S)‐ 4 have been synthesized. ¹H and ⁵¹V NMR spectra in solution are consistent with the formation of Λ and Δ forms of the propeller‐like vanatrane moiety, leading to two diastereomeric conformers for each complex: that is, (P)‐(S,S,S‐Λ)‐ 3 /(P)‐(S,S,S‐Δ)‐ 3 and (M)‐(S,S,S‐Λ)‐ 4 /(M)‐(S,S,S‐Δ)‐ 4 . The Λ/Δ ratio is rather temperature‐insensitive but strongly dependent on the solvent (the de of (M)‐(S,S,S)‐ 4 changes from 0 in benzene to 92 % in DMSO). The solvent therefore controls the preferential clockwise or anticlockwise orientation of the propeller‐like atrane unit. The energy barriers for the Λ?Δ equilibrium were determined by NMR experiments, and the highest ΔG^≠ value (103.7 kJ mol^?1) was obtained for (P)‐(S,S,S)‐ 3 , much higher than those reported for other atrane derivatives. This is attributed to the constraints arising from the cage structure. Determination of the activation parameters provides evidence for a concerted, rather than a stepwise, interconversion mechanism with entropies (ΔS^≠) of ?243 and ?272 J mol^?1 K^?1 for (P)‐(S,S,S)‐ 3 and (M)‐(S,S,S)‐ 4 , respectively. The molecular structure of the (P)‐(S,S,S‐Λ)‐ 3 isomer was solved by X‐ray diffraction and shows a distorted structure with one of the linkers located in the CTV cavity. Complementary quantum chemical calculations were carried out to obtain the energy‐minimized structures of (P)‐(S,S,S)‐ 3 and (M)‐(S,S,S)‐ 4 . Our density functional theory calculations suggest that the (P)‐(S,S,S‐Λ)‐ 3 is favored, in agreement with experimental data. For the M series, a similar strategy was used to extract molecular structures and relative energies. As in the case of the P diastereomer, the Λ form dominates over the Δ one.     

Thermal Behavior of N,N＇Bis[N-（2,2,2-trinitroethyl）-N-nitro]ethylenediamine

The thermal behavior and kinetic parameters of the exothermic decomposition reaction of N‐N‐bis[N‐(2,2,2‐tri‐nitroethyl)‐N‐nitro]ethylenediamine in a temperature‐programmed mode have been investigated by means of differential scanning calorimetry (DSC). The results show that kinetic model function in differential form, apparent activation energy E_a and pre‐exponential factor A of this reaction are 3(1 ‐α)^2/3, 203.67 kJ·mol^?1 and 10^20.61s^?1, respectively. The critical temperature of thermal explosion of the compound is 182.2 °C. The values of ΔS^≠ ΔH^≠ and ΔG^≠ of this reaction are 143.3 J·mol^?1·K^?1, 199.5 kJ·mol^?1 and 135.5 kJ·mol^?1, respectively.     

Proton‐Conducting Magnetic Coordination Polymers

Three isostructural lanthanide‐based two‐ dimensional coordination polymers (CPs) {[Ln₂(L)₃(H₂O)₂]_n ? 2n CH₃OH) ? 2n H₂O} (Ln=Gd³⁺ ( 1 ), Tb³⁺ ( 2 ), Dy³⁺ ( 3 ); H₂L=cyclobutane‐1,1‐dicarboxylic acid) were synthesized by using a low molecular weight dicarboxylate ligand and characterized. Single‐crystal structure analysis showed that in complexes 1 – 3 lanthanide centers are connected by μ₃‐bridging cyclobutanedicarboxylate ligands along the c axis to form a rod‐shaped infinite 1D coordination chain, which is further linked with nearby chains by μ₄‐connected cyclobutanedicarboxylate ligands to form 2D CPs in the bc plane. Viewing the packing of the complexes down the b axis reveals that the lattice methanol molecules are located in the interlayer space between the adjacent 2D layers and form H‐bonds with lattice and coordinated water molecules to form 1D chains. Magnetic properties of complexes 1 – 3 were thoroughly investigated. Complex 1 exhibits dominant ferromagnetic interaction between two nearby gadolinium centers and also acts as a cryogenic magnetic refrigerant having a significant magnetic entropy change of ?ΔS_m=32.8 J kg^?1 K^?1 for ΔH=7 T at 4 K (calculated from isothermal magnetization data). Complex 3 shows slow relaxation of magnetization below 10 K. Impedance analysis revealed that the complexes show humidity‐dependent proton conductivity (σ=1.5×10^?5 S cm^?1 for 1 , σ=2.07×10^?4 S cm^?1 for 2 , and σ=1.1×10^?3 S cm^?1 for 3 ) at elevated temperature (>75 °C). They retain the conductivity for up to 10 h at high temperature and high humidity. Furthermore, the proton conductivity results were correlated with the number of water molecules from the water‐vapor adsorption measurements. Water‐vapor adsorption studies showed hysteretic and two‐step water vapor adsorption (182000 μL g^?1 for 1 , 184000 μL g^?1 for 2 , and 1874000 μL g^?1 for 3 ) in the experimental pressure range. Simulation of water‐vapor adsorption by the Monte Carlo method (for 1 ) confirmed the high density of adsorbed water molecules, preferentially in the interlayer space between the 2D layers.     

Conformation of Peptides Containing a Chiral α‐Ethylated α,α‐Disubstituted α‐Amino Acid: (S)‐α‐Ethylleucine (=(2S)‐2‐Amino‐2‐ethyl‐4‐methylpentanoic Acid) within Sequences of Dimethylglycine and Diethylglycine Residues

An optically active (S)‐α‐ethylleucine ((S)‐αEtLeu) as a chiral α‐ethylated α,α‐disubstituted α‐amino acid was synthesized by means of a chiral acetal auxiliary of (R,R)‐cyclohexane‐1,2‐diol. The chiral α‐ethylated α,α‐disubstituted amino acid (S)‐αEtLeu was introduced into the peptides constructed from 2‐aminoisobutyric acid (=dimethylglycine, Aib), and also into the peptide prepared from diethylglycine (Deg). The X‐ray crystallographic analysis revealed that both right‐handed (P) and left‐handed (M) 3₁₀‐helical structures exist in the solid state of CF₃CO‐(Aib)₂‐[(S)‐αEtLeu]‐(Aib)₂‐OEt ( 14 ) and CF₃CO‐[(S)‐αEtLeu]‐(Deg)₄‐OEt ( 18 ), respectively. The IR, CD, and ¹H‐NMR spectra indicated that the dominant conformation of pentapeptides 14 and CF₃CO‐[(S)‐αEtLeu]‐(Aib)₄‐OEt ( 16 ) in solution is a 3₁₀‐helical structure, and that of 18 in solution is a planar C₅ conformation. The conformation of peptides was also studied by molecular‐mechanics calculations.     

Crystal structure,thermal properties and detonation characterization of bis(5‐amino‐1,2,4‐triazol‐4‐ium‐3‐yl)methane dichloride

Bis(5‐amino‐1,2,4‐triazol‐4‐ium‐3‐yl)methane dichloride (BATZM·Cl₂ or C₅H₁₀N₈²⁺·2Cl^?) was synthesized and crystallized, and the crystal structure was characterized by single‐crystal X‐ray diffraction; it belongs to the space group C2/c (monoclinic) with Z = 4. The structure of BATZM·Cl₂ can be described as a V‐shaped molecule with reasonable chemical geometry and no disorder, and its one‐dimensional structure can be described as a rhombic helix. The specific molar heat capacity (C_p,m) of BATZM·Cl₂ was determined using the continuous C_p mode of a microcalorimeter and theoretical calculations, and the C_p,m value is 276.18 J K^?1 mol^?1 at 298.15 K. The relative deviations between the theoretical and experimental values of C_p,m, H_T – H_298.15K and S_T – S_298.15K of BATZM·Cl₂ are almost equivalent at each temperature. The detonation velocity (D) and detonation pressure (P) of BATZM·Cl₂ were estimated using the nitrogen equivalent equation according to the experimental density; BATZM·Cl₂ has a higher detonation velocity (7143.60 ± 3.66 m s^?1) and detonation pressure (21.49 ± 0.03 GPa) than TNT. The above results for BATZM·Cl₂ are compared with those of bis(5‐amino‐1,2,4‐triazol‐3‐yl)methane (BATZM) and the effect of salt formation on them is discussed.