High pressure studies on new chiral compounds exhibiting TGBA phase

Effects of high pressures on phase sequences of the two homologousn=16 andn=18 of the (3-fluoro-4 ((R) or (S)-methylheptyloxy) 4, (4-fluoro benzoyloxy) tolans) series have been studied. Both compounds exhibit the new twisted Smectic A phase called Twist Grain Boundary TGB_A phase. The high pressure experiments were performed by thermobarometric analysis. The order of the transitions (first or second) have been determined in respect to pressure and temperature. The pressure-temperature phase diagrams show that the TGB_A phase is stabilized by increasing pressure; an inducedN ^* phase appears under high pressure for n=18 leading to the observation of TGB_A-N ^*-I triple point.     

Stable frustrated phases in chiral liquid crystals derived from optically active (R)- and (S)-3-ethylmercapto-2-methylpropionic acids

Highly optically pure (R)- and (S)-3-ethylmercapto-2-methylpropionic acids were synthesized by using optically active (D)- and (L)-2,10-camphorsultams as chiral auxiliaries, respectively. Their derivatives, (R)- and (S)-EMMPNmB (m=6-12), were prepared for investigation. Microscopic texture observations demonstrated that the materials possess three stable frustrated phases: BP, TGB_A* and TGB_C* phases. Interestingly, it was found that the N* phase behaves as an intermediary phase between BP and TGB_A* phases in a rather narrow temperature range (calc. 0.5-1.4°C). A study of the racemic mixture, (±)-EMMPNmB (m=10), indicated that the chirality of the molecule could suppress the formation of smectic phases in the heating process. An increase of alkyl chain length favoured the formation of the TGB phases particularly, in accompaniment with a change of TGB phases from monotropic to enantiotropic. Moderate maximum P _S values (calc. 14-19 nC cm^-2) and apparent tilt angle (calc. 20°) were obtained for the TGB_C* phase in a surface stabilized ferroelectric liquid crystal geometry.     

A specialized apparatus for the study of liquid crystals at high pressures

Abstract

A pressure system specially designed for the study of liquid crystal materials at high pressures up to 4kbar is presented. The pressure system is based on a hydrostatic screw injector and uses either oil or gas as the pressure transmitting medium. The type of measurements which can be performed with the instrument include polarized microscopy, optical spectroscopy, electrooptic and electrical measurements. The different measurements performed place specific constraints on the design of the apparatus and the pressure cells, and details are given. A preliminary study of the smectic A modification of the twist grain boundary phase (TGB_A) at high pressures is presented. The pressure versus temperature phase diagram shows (i) a negative gradient of the TGB_A/isotropic phase boundary line and (ii) that the TGB_A phase does not exist at pressures above about 250 bar. Following Lubensky's analogy between the TGB_A phase and type II superconductors, the disappearance of the TGB_A phase at high pressure may imply that the Landau-Ginsburg parameter K decreases with pressure.     

Evidence of continuous evolution of smectic A2 from smectic Ad

Abstract

We present here precise measurements of the layer spacing for two compounds, viz. 4-n-heptyloxyphenyl-4′-(4″-cyanobenzoyloxy)benzoate and 4-n-undecyloxyphenyl-4′-(4″-cyanobenzyloxy)benzoate. Contrary to earlier reports our data do not show any jump in the layer spacing at the expected A_d-A₂ transition temperature, showing thereby that for both compounds A₂ evolves continuously from the A_d phase.     

Study on the pressure induced charge transfer phase transition in (C5H11)4N(FeFe(C2O2S2)3) by means of μSR spectroscopy

We have investigated the magnetic properties of iron mixed-valence complexes, (n-C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (dto = C₂O₂S₂, n = 3, 5), in which not only a ferromagnetic transition but also a novel charge transfer phase transition (CTPT) take place [1]. This CTPT can be observed under ambient pressure for n = 3, while it appears abruptly above 0.5 GPa for n = 5 [2]. Recently, we have measured the muon spin relaxation (μSR) for the CTPT of n = 3, which revealed the dynamical process of electron-transfer between Fe^II and Fe^III and its frequency was estimated at about 0.1 MHz [3]. To investigate the pressure induced CTPT for n = 5, we carried out the μSR measurement for n = 5 at 150 K between 0.30 and 0.64 GPa with the ⁴He gas-operated pressure system. The asymmetry of the muon spin relaxation for n = 5 with Cu-Be pressure cell was almost constant up to 0.55 GPa, while it rapidly decreased with increasing pressure above 0.60 GPa. This result shows that the applied pressure causes the spin fluctuation due to the CTPT, which induces the decrease of the asymmetry of muon spin relaxation. This experiment can correctly decide the phase transition pressure from the absence to the appearance of the CTPT for n = 5.     

Synthesis and structures of nickel(II) and copper(II) compounds of 5,5,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradecane and the 13-ethyl-5,5,7-trimethyl-homologue

Reduction by NaBH₄ of the imine functions of (5,7,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradec-4-ene)-nickel(II) and -copper(II), and of their 13-ethyl-5,7,7-trimethyl-homologues, yield the nitro-substituted cyclic tetraamine cations (5,5,7,13-tetramethyl-13-nitro-1,4,8,11-tetraazacyclotetradecane)-nickel(II) and -copper(II), [M(neh)]²⁺, and (13-ethyl-5,5,7-trimethyl-homologues, [M(nph)]²⁺, respectively. The nickel(II) cations form square–planar, singlet ground, state salts with poorly coordinating anions and octahedral, triplet ground state, compounds with additional ligands, trans-β-[Ni(neh)A₂], A⁻ = Cl⁻, NCS⁻ and trans-β-[Ni(neh)A₂](ClO₄)₂, X = NH₃, MeCN, all with nitrogen configuration III, 1R,4R,8S,11S = β. With oxalate the chain-polymeric compound catena-trans-β-[Ni(neh)(μ-C₂O₄)]_n · 3n(H₂O) is formed. Folded macrocycle compounds cis-α-[Ni(neh)(C₅H₇O₂)]ClO₄ and cis-α-[{Ni(neh)}₂(C₂O₄)](ClO₄)₂ are formed with the chelates acetylacetonate and oxalate, with configuration 1R,4R,8R,11R = α. These react with HClO₄ to form metastable α-[Ni(neh)](ClO₄)₂ with retention of configuration. The copper(II) cations form crimson salts with poorly coordinating anions and compounds of the type β-[Cu(neh)A]ClO₄ of varying shades of blue with coordinating anions. Structures of singlet ground state square–planar nickel(II) compounds β-[Ni(neh)](ClO₄)₂ · H₂O, β-[Ni(neh)](ClO₄)₂, β-[Ni(neh)]₂[ZnCl₃(OH₂)]₂[ZnCl₄] · H₂O and α-[Ni(neh)](ClO₄)₂, the triplet ground state chain-polymeric compound catena-trans-β-[Ni(neh)(μ-C₂O₄)]_n · 3n(H₂O) and of square–pyramidal β-[Cu(nph)Cl]ClO₄ are reported.     

Effect of the variation of swallow-tailed groups on the mesomorphic and electro-optical properties of chiral compounds derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid

Three homologous series of chiral swallow-tailed compounds, alkyl (S)-2-{6-[4-(4′-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionates, (S)HNP(p,n,q) derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid in conjugation with a variety of swallow-tailed groups, attached to the external side of the chiral centre, have been synthesized and their mesomorphic and electro-optical properties studied. Both (S)HNP(p,1,2) and (S)HNP(p,1,3) exhibited an enantiotropic antiferroelectric SmC*_A phase. This implys that the swallow-tailed groups in the molecules favour zigzag pairing of the molecules in the smectic phase. The maximum P _S values of compounds (S)HNP(p,1,2) in the antiferroelectric phase were measured in the range 21–30 nC cm^-2; those of compounds (S)HNP(p,1,3) were in the range 15–23 nC cm^-2, indicating that these chiral compounds possess low polarity. The electro-optical response of the compounds in the antiferroelectric SmC*_A phase displayed thresholdless V-shaped switching.     

Multianvil high-pressure/high-temperature synthesis, crystal structure, and thermal behaviour of the rare-earth borogermanate Ce6(BO4)2Ge9O22

The new monoclinic cerium borogermanate Ce₆(BO₄)₂Ge₉O₂₂ was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 10.5 GPa and 1200 °C. Ce₆(BO₄)₂Ge₉O₂₂ crystallizes with two formula units in the space group P2₁/n with lattice parameters a=877.0(2), b=1079.4(2), c=1079.1(2) pm, and β=95.94(3)°. As the parameter pressure favours the formation of compounds with cations possessing high coordination numbers, it was possible to produce simultaneously BO₄-tetrahedra and GeO₆-octahedra in one and the same borogermanate for the first time. Furthermore, the cerium atoms show high coordination numbers (C.N.: 9 and 11), and one oxygen site bridges one boron and two germanium atoms (O^[3]), which is observed here for the first time. Besides a structural discussion, temperature-dependent X-ray powder diffraction data are presented, demonstrating the metastable character of this high-pressure phase.     

Phase-transition studies of 5O.5 and 9O.4

As part of our detailed comparative studies of groups of liquid-crystalline compounds that belong to a homologous series, we present phase-transition studies of the compounds N-(4-n-pentyloxybenzylidene)4′-n-pentylaniline (5O.5) and N-(4-n-nonyloxybenzylidene)4′-n-butylaniline (9O.4) using different experimental techniques. The compound 5O.5 is reported to exhibit a phase sequence N, S_A, S_C, S_B and S_G, while 90.4 shows the sequence S_A, S_F and S_G. The salient features of our work on 5O.5 are (i) a new smectic F phase is found in place of the reported smectic B phase, which is confirmed by both miscibility and X-ray studies; (ii) the formation of smectic-C-like short-range order in the nematic phase well above the S_A-N transition; and (iii) a large tilt-angle variation in the smectic C phase (0–23·5°C) in a small temperature range (4·1°C). The phase changes across the S_A-I transition, and for the first time across S_F-S_A transition, are carried out by volumetric studies. The detailed inferences of these are also presented.     

Optically active cyclic poly(ether sulfone)s based on chiral 1,1′-bi-2-naphthol

Optically active cyclic poly(ether sulfone)s are prepared from 4-fluorophenyl sulfone and (R)- or (S)-1,1′-bi-2-naphthol. The measurement of MALDI-TOF MS shows that the product is composed of a series of cyclic and linear oligomers where the repeating unit number (n) is from 2 to 12, from which the cyclic dimers (n=2), and cyclic trimer (n=3) have been separated from their homologous compounds by TLC successfully. Specific optical rotation [α]_D²⁵ is −583.0 for (R)-cyclic dimer, +588.0 for (S)-cyclic dimer, +22.7 for (R)-cyclic trimer, and −20.3 for (S)-cyclic trimer. Their properties are also determined by other methods, such as ¹H NMR and CD etc.     

Twist-grain boundary phase induced by Au nanoparticles in a chiral liquid crystal host

We report on the stabilisation of the liquid-crystalline, twist-grain boundary A (TGB_A) phase in mixtures of a chiral liquid crystal and surface-functionalised spherical Au nanoparticles (NPs) of 10 nm diameter. The results, obtained by calorimetric, optical, small-angle X-ray and plasmon resonance measurements, demonstrate that a TGB_A phase, which is metastable for the pure liquid crystal host, can be effectively stabilised for a 3 K range in the presence of NPs. Moreover, the role of NPs size on the TGB_A stabilisation is briefly discussed.     

Crystal Structure and Electrical Conductivity of Palladium Sulfide BronzesMP3S4(M=La,Nd, and Eu)

Palladium sulfide bronzesMPd₃S₄(M=La, Nd, and Eu) were prepared in single phase. The bronzes are cubic with twoMatoms in (0,0,0; 1/2,1/2,1/2) and six palladium atoms in (1/4,0,1/2⥀) positions. The sulfur positions (x,x,x⥀) were determined with a guide of theRfactors. Thexvalues were 1/4 for La and Nd compounds (i.e., space groupPm3n), while a plot of theRfactors of EuPd₃S₄gave a very broad curve showing thexvalue rather displaced from 1/4. This result is considered to be associated with the mixed valency of europium (Eu²⁺and Eu³⁺) in this compound.MPd₃S₄(M=La, Nd, and Eu) exhibited metallic conductions with the electrical conductivities decreasing with increasing temperature in the experimental range from ∼15 K to room temperature. At 300 K, σ were 2.77, 2.42, and 2.28 S m⁻¹forMPd₃S₄(M=La, Nd, and Eu), respectively. From the Hall coefficient measurements, the carriers were found to be the electrons with their numbers 1.71, 1.68, and 0.82 per unit cell of the crystals ofM=La, Nd, and Eu compounds, respectively. These values suggest the formulas to beM³⁺(Pd²⁺₃e⁻)S²⁻₄for La and Nd compounds, and to be Eu²⁺_0.5Eu³⁺_0.5(Pd²⁺₃e⁻_0.5)S²⁻₄for Eu compound.     

Synthesis of linear and cyclic homo-β-peptides based on a binaphthylic β-amino acid with only axial chirality

The terminally protected, linear, homo-β-peptides Boc-[(R)-β^2,2-HBin]_n-OMe (n = 2–6) as well as the cyclic homo-β-peptides c[(R)-β^2,2-HBin]₃ and c[(S)-β^2,2-HBin]₄, all derived from the 2′,1′:1,2;1″,2″:3,4-dinaphthcyclohepta-1,3-diene-6-aminomethyl-6-carboxylic acid residue β^2,2-HBin possessing only axial chirality, have been synthesized in solution by the EDC/AtOH coupling method for chain elongation, and by cyclization of pentafluorophenyl esters. A conformational analysis suggested the concomitant occurrence of different intramolecularly H-bonded forms for the linear oligomers in solution.     

Insertion Reactions of Carbon Disulfide into Mg‐C and Mg‐N Bonds: Syntheses and Structural Determinations of Mg(S2CY)2(THF)n(Y=NEt2, NiPr2, iPr,Ph) and BrMg(S2CZ)(THF)3(Z=Ph,iPr)

The insertion reaction of CS₂ with Mg(NR₂)₂ (R= Et, ⁱPr), MgR′₂ (R′= Et, Ph) and R″MgBr (R″= ⁱPr, Ph) respectively lead solid products, Mg(S₂CNR₂)₂(THF)_n ( 1 : R= Et, n=2; 2 : R= ⁱPr, n=1), Mg(S₂C′R)₂(THF)₂ ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S₂C″R) (THF)₃ ( 5 : ″R= ⁱPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with ¹H, ¹³C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography.     

Solid-state structure determination and solution-state NMR characterization of the (2R,4R)/(2S,4S)- and (2R,4S)/(2S,4R)-diastereomers of the agricultural fungicide propiconazole,the (2R,4S)/(2S,4R)-symmetrical triazole constitutional isomer,and a ditriazole analogue

Single-crystal X-ray diffraction analysis was used to determine the structure of a racemic diastereomer of the agricultural fungicide propiconazole [1-(2-(2,4-dichlorophenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole] and of two by-products (a symmetrical 1,3,4-triazole racemic-constitutional isomer and a propiconazole ditriazole analogue). All three crystalline racemic-diastereomers had (2R,4S)/(2S,4R)-stereochemistry in which then-propyl group was observed in atrans-to-phenyl disposition. Propiconazole (2R,4S)/(2S,4R)-diastereomer gives crystals belonging to the monoclinic space group P2₁,/a, and, at 293 K,a=8.1192(3),b=18.9769(6),c=10.7137(4) å,Β=99.765(3)?,V=1626.8(1) å³, Z=4,R(F)=0.060, andR _w(F)=0.058. The constitutional isomer by-product (2R,4S)/(2S,4R)-1-(2-(2,4-dichlorophenyl)-4-n-pro-pyl-1,3-dioxolane-2-yl-methyl)-1-H-1,3,4-triazole gives crystals belonging to the monoclinic space group P2₁/n, and, at 293 K,a=11.1763(6),b=10.7716(4),c=14.5804(8) å,Β=107.445(4)?,V=1674.6(1) å³, Z=4,R(F)=0.043, andR _w(F)=0.043. The ditriazole byproduct (2R,4S)/(2S,4R)-1-(2-(2-chloro-4-(1,2,4-triazole-1-yl)phenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole gives crystals belonging to the triclinic space groupP¯ 1, and, at 193 K,a=5.3329(8),b=8.3738(7),c=20.240(2) å, α=84.213(6)?,Β=87.20(1)?,γ=86.23(1)?,V=896.5(2) å³, Z=2,R(F)=0.046, andR _w(F)=0.051. The presence of both propiconazole (2R.4S)- and (2S,4R)-enantiomers enables the formation of a crystalline racemic modification, while the diastereomeric propiconazole (2R,4R)- and (2S,4S)-enantiomers are viscous oils. In the absence of its enantiomorphic partner, the propiconazole (2R,4S)- or (2S,4R)-enantiomers remain as viscous oils rather than form chiral crystals.     

Synthesis and structure of chiral-at-metal complexes with the ligand (S)-2-[(Sp)-2-(diphenylphosphino)ferrocenyl]-4-isopropyloxazoline

Half-sandwich complexes of formula [(ηⁿ-ring)MClL]PF₆ [L = (S)-2-[(S_p)-2-(diphenylphosphino)ferrocenyl]-4-isopropyloxazoline; (ηⁿ-ring)M = (η⁵-C₅Me₅)Rh; (η⁵-C₅Me₅)Ir; (η⁶-p-MeC₆H₄iPr)Ru; (η⁶-p-MeC₆H₄iPr)Os] have been prepared and spectroscopically characterised. The molecular structures of the rhodium and iridium compounds have been determined by X-ray crystallography. The related solvate complexes [(η⁵-C₅Me₅)ML(Me₂CO)]²⁺ (M = Rh, Ir) are active catalysts for the Diels-Alder reaction between methacrolein and cyclopentadiene.     

Crystal structures of CsFe2S3 and RbFe2S3: synthetic analogs of rasvumite KFe2S3

The isostructural alkali thioferrate compounds CsFe₂S₃, RbFe₂S₃ and KFe₂S₃ have been synthesized by reacting Fe and S with their corresponding AFeS₂ (A=K, Rb, Cs) precursors. The crystal structures of these and binary compounds of intermediate composition were determined by Rietveld analysis of laboratory powder X-ray diffraction patterns. All of the synthesized compounds adopt the space group Cmcm (#63), Z=4 with: a=9.5193(8) Å, b=11.5826(10) Å, c=5.4820(4) Å for CsFe₂S₃; a=9.2202(7) Å, b=11.2429(9) Å, c=5.4450(3) Å for RbFe₂S₃; and a=9.0415(13) Å, b=11.0298(17) Å, c=5.4177(6) Å for KFe₂S₃. These mixed valence alkali thioferrates show regular changes in cell dimensions, AS₁₀ (A=K, Rb, Cs) polyhedron volumes, polyhedron distortion parameters, and calculated oxidation state of Fe with respect to increasing size of the alkali element cation. The calculated empirical oxidation state of iron varies from +2.618 (CsFe₂S₃), through +2.666 (RbFe₂S₃) to +2.77 (KFe₂S₃).     

LOCATION OF THE CAROTENOID 2Ag-STATE AND ITS ROLE IN PHOTOSYNTHESIS

The location of the carotenoid 2A_g-state (S₁) was studied by fluorescence spectroscopy in two series of carotenoids. One consisted of natural polyenes like phytoene, phytofluene, β-carotene, and neurosporene, and the other of minicarotenes, i.e., compounds similar to β-carotene, but with a smaller number of double bonds (n=3–9). A decrease of the S₁-S₀ energy gap with n was observed in both series, and extrapolation to n= 11 gave the energies 14 500 and 13 200 cm^?1 for β-carotene and lycopene, respectively. The neurosporene S₁ state was located at ca 16 000 cm^?1. A good relationship between the nonradiative relaxation rate and the number of conjugation was observed. The rate increased by a factor of 2.5 per double bond. The possible role of the S₁ state in reversible carotenoid ← chlorophyll electron-exchange energy transfer is discussed.     

Ionic liquid-phase asymmetric catalytic hydrogenation: hydrogen concentration effects on enantioselectivity

Molecular hydrogen is almost four times more soluble in the ionic liquid 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI·BF₄) than in its hexafluorophosphate (BMI·PF₆) analogue at the same pressure. The Henry coefficient solubility constant for the solution BMI·BF₄/H₂ is K=3.0×10⁻³ mol L⁻¹ atm⁻¹ and 8.8×10⁻⁴ mol L⁻¹ atm⁻¹ for BMI·PF₆/H₂, at room temperature. The asymmetric hydrogenation of (Z)-α-acetamido cinnamic acid and kinetic resolution of (±)-methyl-3-hydroxy-2-methylenebutanoate by (−)-1,2-bis((2R,5R)-2,5-diethylphospholano)benzene(cyclooctadiene)rhodium(I) trifluoromethanesulfonate and dichloro[(S)-(−)-2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl]ruthenium(II) complexes immobilised in BMI·PF₆ and BMI·BF₄ were investigated. Remarkable effects in the conversion and enantioselectivity of these reactions were observed as a function of molecular hydrogen concentration in the ionic phase rather than pressure in the gas phase.     

New compounds in the cesium sulfobromide rhenium octahedral cluster chemistry: syntheses and crystal structures of Cs4Re6S8Br6 and Cs2Re6S8Br4

The exploration of the CsReSBr system, in order to identify new phases based on octahedral cluster anions, has produced single crystals of Cs₄Re₆S₈Br₆ (1) (trigonal, space group P-6c2, a=9.7825 (3) Å, c=18.7843 (5) Å, V=1556.77 (1) ų, Z=2, density=5.09 g cm⁻³, μ=36.07 mm⁻¹) and Cs₂Re₆S₈Br₄ (2) (monoclinic, space group P2₁/n, a=6.3664 (1) Å, b=18.4483 (4) Å, c=9.3094 (2) Å, β=104.2618 (8)°, V=1059.69 (4) ų, Z=2, density=6.14 g cm⁻³, μ=45.83 mm⁻¹). These two compounds have been obtained by high-temperature solid state route. Their structures have been solved and refined from single crystal X-ray diffraction data. The structure of Cs₄Re₆S₈Br₆ presents isolated anionic cluster units inscribed in a (Cs⁺)₁₂ cuboctahedron and the one of Cs₂Re₆S₈Br₄ exhibits ReS^i-a,a-iRe inter-unit bridges. The framework of the latter presents then a strongly 1-D character.