Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

X-ray diffraction investigation of perfluoro-4-methylenecyclohexa-2,5-dienones

Perfluorinated 8-phenyl-7,8-diethylbicyclo[4.2.0]octa-1,4,6-trien-3-one (3), 2-(4-oxocyclohexa-2,5-dienylidene)-1,1-diethylbenzocyclobutene (4) and 2-(4-oxocyclohexa-2,5-dienylidene)-5-(2-phenyl-cis-1,2-diethylbenzocyclobuten-1-yloxy)-1,1-diethylbenzocyclobutene (5), including the 4-methylencyclohexa-2,5-dienone fragment, were prepared by the reaction of perfluoro-1,1-(1) and-1,2-diethylbenzocyclobutene (2) with pentafluorobenzene in SbF₅. Single crystal X-ray diffraction study of compounds 3–5 revealed that the oxygen atom of the C=O group participated in the formation of supramolecular architectures in all three compounds, and C=O…π bonding may be considered as the corresponding synthon (with increased separation in the case of compound 5). C-F…π bonding acts as a second synthon. F…F interactions in crystals 3–5 were classified as stabilizing or enforced.     

Reactions of azulenes with 1,2-diaryl-1,2-ethanediols in methanol in the presence of hydrochloric acid: comparative studies on products, crystal structures, and spectroscopic and electrochemical properties

Although reaction of guaiazulene (1a) with 1,2-diphenyl-1,2-ethanediol (2a) in methanol in the presence of hydrochloric acid at 60 °C for 3 h under aerobic conditions gives no product, reaction of 1a with 1,2-bis(4-methoxyphenyl)-1,2-ethanediol (2b) under the same reaction conditions as 2a gives a new ethylene derivative, 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (3), in 97% yield. Similarly, reaction of methyl azulene-1-carboxylate (1b) with 2b under the same reaction conditions as 1a gives no product; however, reactions of 1-chloroazulene (1c) and the parent azulene (1d) with 2b under the same reaction conditions as 1a give 2-[3-(1-chloroazulenyl)]-1,1-bis(4-methoxyphenyl)ethylene (4) (81% yield) and 2-azulenyl-1,1-bis(4-methoxyphenyl)ethylene (5) (15% yield), respectively. Along with the above reactions, reactions of 1a with 1,2-bis(4-hydroxyphenyl)-1,2-ethanediol (2c) and 1-[4-(dimethylamino)phenyl]-2-phenyl-1,2-ethanediol (2d) under the same reaction conditions as 2b give 2-(3-guaiazulenyl)-1,1-bis(4-hydroxyphenyl)ethylene (6) (73% yield) and (Z)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1-phenylethylene (7) (17% yield), respectively. Comparative studies of the above reaction products and their yields, crystal structures, spectroscopic and electrochemical properties are reported and, further, a plausible reaction pathway for the formation of the products 3-7 is described.     

Iron complexes of terdentate nitrogen ligands: formation and X-ray structure of three new dicationic complexes

Dicationic iron complexes were obtained upon complexation of the ligands 6,6″-di(p-tolyl)-2,2′:6′,2″-terpyridine (L¹) or 2,6-bis-(3-mesitylpyrazol-1-yl)pyridine (L²) with iron dichloride or iron trichloride. They were characterized by X-ray diffraction and FT-IR spectroscopy. Single crystal structure determinations of , and all show six-coordinate metal center. These complexes were obtained from L¹FeCl₂ and L²FeCl₂ during recrystallization attempts. (L¹)₂Fe²⁺ was shown to be a high-spin complex, whereas (L²)₂Fe²⁺ was shown to be low-spin. For , two independent dications of very similar geometry but with distinctive distortion were observed by X-ray analysis.     

FT-Raman Spectroscopic Investigations on the Organic Crosslinking in Hybrid Polymers Part II: Reactions of Epoxy Silanes

FT-Raman spectroscopy was used together with supplementary ¹³C-NMR measurements to analyze the reaction of the epoxy moieties of 3-glycidoxypropyltrimethoxysilane and 5,6-epoxyhexyltrimethoxysilane during sol-gel processing. Based on the results for simple epoxides reported in Riegel, Kiefer, Hofacker and Schottner (Appl. Spec. 54, 1384 (2000)) the formation of -hydroxy methyl ethers can be derived. An additional condensation of the epoxy rings yielding a mixture of oligo ethers is considered very probable from the Raman measurements. Raman and NMR assignments are proposed for 5,6-epoxyhexyltrimethoxysilane.     

X-ray diffraction structural investigation of two hafnium(IV) complexes with dipivaloylmethane

Synthesis and single crystal X-ray diffraction study of hafnium(IV) dipivaloylmethanate Hf(dpm)₄ and chloro-tris-(dipivaloylmethanato)hafnium(IV) Hf(dpm)₃Cl have been carried out. Crystal data: a = 22.6606(5) Å, b = 11.3990(4) Å, c = 19.8513(7) Å, β = 106.458(1)°, Pc, Z = 4, d _calc = 1.231 g/cm³, R = 0.075 for C₄₄H₇₆HfO₈; a = 10.6376(13) Å, b = 10.6701(10) Å, c = 19.4400(22) Å, α = 74.970(3)°, β = 75.672(3)°, γ = 61.725(2)°, P-1, Z = 2, d _calc = 1.366 g/cm³, R = 0.031 for C₃₃H₅₇ClHfO₆. The structures are molecular and are built from discrete mononuclear complexes joined by van der Waals interactions. Disordering of carbon atoms preserving at low temperature is observed for the compound Hf(dpm)₄. It has been found out that the structure contains two crystallographically unique complexes of hafnium(IV) with central atoms coordinated with eight oxygen atoms of four dipivaloylmethane ligands, bond lengths Hf-O fall within 2.084–2.222 Å, the distances Hf...Hf between the molecules are 10.07–13.87 Å. In Hf(dpm)₃Cl the hafnium atom is seven-coordinated with six oxygen atoms of three β-diketonate ligands and one chlorine atom, the distances Hf-O fall within 2.087–2.179 Å, the lengths of the bond Hf-Cl for two crystallographically independent molecules Hf(1) and Hf(2) are 2.466 Å and 2.442 Å, respectively.     

Syntheses, characterization, X-ray crystal structures and emission properties of five oxovanadium(V) complexes with pyridyl/pyrimidyl-pyrazole derived ditopic ligands

Four oxovanadium(V) complexes of heterocycle based ditopic ligands PyPzOAP (N-[amino(pyridin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid), PyPzOAPz (N-[amino(pyrazin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid), PymPzOAP (N-[amino(pyridin-2-yl)methylidene]-1-(4,6-dimethylpyrimidin-2-yl)-5-methyl-1H-pyrazole-3-carbohydrazonic acid) and PyPzCAP (5-methyl-1-(pyridin-2-yl)-N′-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide) and a binuclear (di-μ-oxo) oxovanadium(V) complex of the ligand PymPzCAP (1-(4,6-dimethylpyrimidin-2-yl)-5-methyl-N′-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide) have been investigated. The ligands act as uninegative NNO tridentates donors for the VO₂⁺ ion exhibiting their monotopicity. The ligands show varying emission properties due to the presence of fluophoric groups like 1-(2-pyridyl)pyrazole or 1-(2-pyrimidyl)pyrazole. The vanadium(V) complexes show fluorescence quenching with respect to the used ligands to a varying extent. The complexes were characterized by UV-Vis, IR, cyclic voltammetry and X-ray crystallography.     

New chiral bidentate ligands containing thiazolyl and pyridyl donors for copper-catalyzed asymmetric allylic oxidation of cyclohexene

Chiral bidentate ligands 1-3, which contain a combination of thiazolyl and pyridyl donors units, were prepared. The syntheses are facile and being based on Kröhnke condensation of a pinene derivative to form the pyridine ring. Modification at the 8-position of the tetrahydroquinoline ring can be carried out by alkylation reaction with 2a and 3a but not 1a. The structure of a copper(II) perchlorate complex of 1a was characterized with X-ray crystallography, which reveals the binding of the pyridyl-thiazole as a N-N donors at the copper center. The copper(I) thiazolyl-pyridine complexes prepared in situ are active catalysts in the enantioselective allylic oxidation of cyclohexene using tert-butyl perbenzoate as the oxidant. The isolated yields of the allylic benzoate were up to 98%, and enantioselectivity was up to 62% e.e.     

Organic fluorines as halogen bond donors: Theoretical study and crystallographic evidence

Organic fluorines usually cannot act as halogen bond donors, as a result of the extreme electronegativity and least polarizability of the fluorine atom. However, when the electronegative ability of the substituents bound to the carbon atom is very strong, organic fluorines do show positive electrostatic potentials (ESPs) along the C? F bond and thus can form halogen bonds with electron donors. In this work, the effects of six different substituents, i.e., NO₂, CF₃, CN, COOH, CHO, and CCH, on the ESPs of the F atom were studied using the M06‐2x method. When two or three substituents with very strong electron‐withdrawing ability, such as NO₂ and CN, are linked to the C atom, positive ESPs take place on the outermost portion of the F atom. However, the ESPs remain negative along the C? F bond with the introduction of relatively weak electron‐withdrawing substituents, irrespective of the number of the subsituents. In addition, some complexes between fluorinated molecules with positive ESPs on the F atom and NH₃ were calculated, to characterize the structural and energetic features of these specific halogen bonds. Finally, some crystal structures extracted from the Cambridge Structural Database were selected to provide experimental evidence of these interactions involving the C? F bond. The results presented in this work are very important for the modern definition of halogen bonding as well as for the development of pharmaceuticals and a wide range of functional material. © 2015 Wiley Periodicals, Inc.     

Exploiting the versatility of pyridyl ligands for the preparation of diorganotin (IV) adducts: spectral,crystallographic and Hirshfeld surface analysis studies

Diorganotin (IV) complexes SnR₂X₂ (R = Me, Ph; X = Cl, NCS) form a series of versatile complexes when react with bidentate substituted pyridyl ligands. The reaction of dimethyltin dichloride with 5,5′‐dimethyl‐2,2′‐bipyridine (5,5′‐Me₂bpy) resulted in the formation of [SnMe₂Cl₂(5,5′‐Me₂bpy)] ( 1 ). Moreover, the reaction of SnMe₂(NSC)₂ with 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (bu₂bpy), 1,10‐phenanthroline (phen) and 4,7‐diphenyl‐1,10‐phenanthroline (bphen) affords the hexa‐coordinated complexes [SnMe₂(NCS)₂(bu₂bpy)] ( 2 ), [SnMe₂(NCS)₂(phen)] ( 3 ) and [SnMe₂(NCS)₂(bphen)] ( 4 ), respectively. The resulting complexes have been characterized using elemental analysis, IR, multinuclear NMR (¹H, ¹³C, ¹¹⁹Sn) and DEPT‐135^° NMR spectroscopy. On the other hand, the reaction of diphenyltin dichloride with 2,2′‐biquinoline (biq) and 4,7‐phenantroline (4,7‐phen) led to the formation of polymeric complexes of [SnPh₂Cl₂(4,7‐phen)]_n ( 5 ) and [SnPh₂Cl₂(biq)]_n ( 6 ). The NMR spectra, however, reveal the ligand lability in solution and suggest a coordination number of 5 . The X‐ray crystal structures of complexes [SnMe₂Cl₂(5,5′‐Me₂bpy)] ( 1 ), [SnMe₂(NCS)₂(bu₂bpy)] ( 2 ) and [SnMe₂(NCS)₂(bphen)] ( 4 ) have been determined which reveal that the geometry around the tin atom is distorted octahedral with trans‐[SnMe₂] configuration. Interestingly, the crystal structure of (H₂biq)₂[SnPh₂Cl₄]?2CHCl₃ ( 7 ) was characterized by X‐ray crystallography from a chloroform solution of [SnPh₂Cl₂(biq)]_n ( 6 ) indicating the formation of doubly protonated [H₂biq]⁺ and [Ph₂SnCl₄]^2? which are stabilized by a network of hydrogen bonds with a feature of trans‐[SnPh₂]. The 3D Hirshfeld surface analysis and 2D fingerprint maps were used for quantitative mapping out of the intermolecular interactions for 1 , 2 , 4 and 7 which show the presence of π‐π and hydrogen bonding interactions which are associated between donor and acceptor atoms (N, S, Cl) in the solid state.     

Synthesis and characterization of Zr(IV) and Y(III) complexes with monocyclopentadienyl ligands containing an additional site tethered by a coordinating 2,6-pyridine bridge. X-ray crystal structures of the zirconium complexes

A new monocyclopentadienyl ligand containing an additional site tethered by a coordinating 2,6-pyridine unit has been prepared, rac-2-(1′-hydroxy-2′,2′-dimethylpropyl)-6-(1″,1″-dimethyl-cyclopentadienylmethyl) pyridine dilithium salt, LLi₂ (rac-4) that is analogous to the ligands present in CGC. After reacting the dilithium salt of the ligand with ZrCl₄ in a molar ratio of 1:1 in THF the complex LZrCl₂·THF (rac-5) was obtained which forms an insoluble oligomeric species after the loss of THF upon purification. From the mater liquor two crystalline species of the formula LHZrCl₃ (rac-6) and LH₂ZrCl₄·THF (rac-7) were isolated, whose X-ray crystal structures are reported. The reaction of LLi₂ with Y(OTf)₃ afforded the probably dimeric species [LYOTf]₂ (rac-8) from which the complex [LY(CH₂Si(CH₃)₃)]₂ (rac-9) was obtained after reaction with LiCH₂Si(CH₃)₃.     

Synthesis and characterization of novel pyridyl/naphthyl/(diphenyl)methylseleno substituted alkanoic acids: X-ray structure of 2-pyridylselenoethanoic acid, 2-naphthylselenoethanoic acid and 2-(diphenyl)methylselenoethanoic acid

A number of novel and synthetically important pyridyl/naphthyl/(diphenyl)methylseleno substituted alkanoic acids (20-25) have been synthesized using an efficient and operationally simple strategy. Starting substrates, ethyl pyridyl/naphthyl/(diphenyl)methylseleno substituted alkanoates (8-13) were easily prepared by treatment of ethyl chloroalkanoates 7(a-c) with nucleophilic selenium reagent RSeNa⁺, generated from the cleavage of dipyridyl/dinaphthyl/bis(diphenylmethyl) diselenide (1-6) with sodium borohydride in ethanol. The ethyl pyridyl/naphthyl/(diphenyl)methylseleno substituted alkanoates (8-13) on basic hydrolysis and subsequent acidification afford pyridyl/naphthyl/(diphenyl) methylseleno substituted alkanoic acids (20-25) in excellent yields. These selenoalkanoates (8-13) and selenoalkanoic acids (20-25) have been characterized by elemental analysis and various spectroscopic techniques viz. NMR (¹H, ¹³C and ⁷⁷Se), IR and mass spectrometry. The molecular structure of 2-pyridylselenoethanoic acid (20a), 2-naphthylselenoethanoic acid (23a) and 2-(diphenyl)methylselenoethanoic acid (24a) has also been established with the help of single crystal X-ray analysis.     

天然产C19-二萜生物碱的单晶X-射线衍射分析

本文综述了2002年以前45个天然产C19-二萜生物碱的单晶X-射线衍射分析结果及其结构特点。     

Search for nematic biaxiality in bent-core mesogens: an X-ray diffraction perspective

ABSTRACT

Since its theoretical prediction in 1970, the search for the biaxial nematic phase in thermotropic systems has challenged generations of liquid crystal scientists. Over the last 10 years, bent-core mesogens have drawn much interest as promising candidates for nematic biaxiality. However, despite a number of disputed claims, conclusive evidence of proper (spontaneous and macroscopic) biaxial order in these materials is still missing. By contrast, it is now widely recognised that biaxiality exists on a local scale, in the form of nano-sized clusters of molecules (cybotactic groups) possessing smectic-like positional order and biaxial orientational order. This article provides a review of X-ray diffraction studies on biaxiality and cybotaxis in bent-core nematics, discussing the most relevant issues related to this research field.     

The Gomberg-type dimerization of bifluorenylidene radicals: an X-ray crystallographic investigation

The reaction of phenylethynyllithium with 9-bromofluorene yields 9,9′-bifluorenylidene, 8, 9,9′-bifluorenyl, 9, and a molecule 10, of formula C₅₂H₃₂, in which coupling has occurred between a 9,9′-bifluorenyl fragment and a 9,9′-bifluorenylidene moiety such that a C(9) position of the former is attached to a C(3) site of the latter. This parallels the unsymmetrical radical coupling of triphenylmethyl radicals, which leads to the Gomberg dimer, rather than hexaphenylethane. The structure of 10 has been elucidated by X-ray crystallography, and a mechanistic rationale is offered.     

Tautomeric polymorphism in salicylideneamine derivatives: an X-ray diffraction and solid-state NMR study

The crystal structure of the N-(3-hydroxysalicylidene)-4-methoxyaniline has been studied by single-crystal X-ray diffraction and solid-state NMR spectroscopy. This is the first example of a Schiff base derived from 3-hydroxysalicylaldehyde which displays in the asymmetric unit, four distinct molecules linked together in the crystal lattice by two types of intermolecular O–HO hydrogen bonds and formed by two independent tetramers. The ¹³C CPMAS NMR study corroborates the above results; the presence of different tautomeric equilibria in the same crystal structure is demonstrated and a qualitative estimation of the equilibrium mixture composition is given.     

Identification of steel by X-ray fluorescence analysis with a pyroelectric X-ray generator

An application of X-ray fluorescence analysis with a pyroelectric X-ray generator is presented. Steel standard samples were identified by X-ray fluorescence analysis with this novel X-ray generator to check its capability for performing qualitative and quantitative analysis as an X-ray source for X-ray fluorescence spectrometers. Cr, Ni, V, Co, and W were detected in steel standard samples. V and Cr can be detected even when the content is below 1%. Although it is difficult to detect minor elements because of the low power of the excitation X-rays, it is possible to identify the analyzed samples on the basis of major elements at the percentage level. The pyroelectric X-ray generator is very suitable for portable X-ray fluorescence spectrometers.     

Reactions of guaiazulene with methyl terephthalaldehydate and 2-hydroxy- and 4-hydroxybenzaldehydes in methanol in the presence of hexafluorophosphoric acid: comparative studies on molecular structures and spectroscopic, chemical and electrochemical properties of monocarbocations stabilized by 3-guaiazulenyl and phenyl groups

Reaction of guaiazulene (1) with methyl terephthalaldehydate (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 2 h under aerobic conditions gives (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (5) in 94% yield. Similarly, reactions of 1 with 2-hydroxybenzaldehyde (3) and 4-hydroxybenzaldehyde (4) under the same reaction conditions as 2 give (3-guaiazulenyl)(2-hydroxyphenyl)methylium hexafluorophosphate (6) and (3-guaiazulenyl)(4-hydroxyphenyl)methylium hexafluorophosphate (7) in 89 and 97% yields, respectively. Comparative studies on the molecular structures as well as the spectroscopic, chemical and electrochemical properties of the monocarbocation compounds 5-7 stabilized by 3-guaiazulenyl and 4-(methoxycarbonyl)phenyl (or 2-hydroxy- or 4-hydroxyphenyl) groups are reported.     

A facile preparation, the crystal structure, the chemical and electrochemical properties of [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate

Reaction of guaiazulene (1) with p-dimethylaminobenzaldehyde in methanol in the presence of tetrafluoroboric acid gives the title monocarbocation compound, [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate (2), in 90% yield. The title investigations of compound 2 compared with those of two other monocarbocations stabilized by a 3-guaiazulenyl group (i.e. phenyl-3-guaiazulenylmethyl and [4-(isopropyl)phenyl]-3-guaiazulenylmethyl cations) are reported.