The structure of β-diketones related to curcumin determined by X-ray crystallography,NMR (solution and solid state) and theoretical calculations

Structural Chemistry - Structural data are reported on sixteen ketoenols of β-diketones: solution NMR, solid-state NMR (CPMAS and MAS) and X-ray crystallography (four compounds, where three...     

Vanadiumoxo–aroylhydrazone complexes: Synthesis,structure and DFT calculations

The aroylhydrazone Schiff base ligands (E)-N’-(2-hydroxybenzylidene)benzohydrazide = H₂L¹, (E)-N’-(2-hydroxy-3-methoxybenzylidene)benzohydrazide = H₂L² and = (E)-N’-(5-bromo-2-hydroxybenzylidene)benzohydrazide = H₂L³ gave the vanadium(V)oxo-aroylhydrazone complexes [V^VOL¹(OCH₃)(OHCH₃] (1), [V^VOL²(OCH₃)(OHCH₃]·CH₃OH (2) and [V^VOL³(OCH₃)(OHCH₃] (3) on reaction with vanadium(IV) oxide acetylacetonate. The complexes were characterized by spectroscopic methods in the solid state (IR) and in solution (UV–Vis, ¹H NMR). Single crystal X-ray analysis was performed with 3. In methanol solution six-coordinated V^VOL³(OCH₃)(OHCH₃) was formed. V^IV was oxidized to V^v by aerial oxygen in the synthesis. In the VO₅N coordination sphere the alcohol oxygen lies trans to the oxo oxygen. The general V–O bond length order is oxo < methoxylato < phenoxidic < enolato < alcoholic. The complexes are mononuclear, but intermolecular O–H?N hydrogen bonding affords a zigzag chain. DFT calculations on complex 3 reproduced the geometric parameters, IR and UV–Vis spectroscopic data well in a reasonable range.     

The crystal structure of a valinomycin•2Ca2+ complex and the multi-step solution equilibria in acetonitrile characterised by 1H NMR,UV–Vis,and mass spectrometry

Valinomycin is a well-known potassium-selective ion carrier, but the nature of its direct interaction with calcium ion, another biologically important cation, is also of considerable interest. We have determined the first crystal structure of a valinomycin–calcium complex, which crystallises exclusively as a 1:2 valinomycin:Ca²⁺ complex, [VCa₂(OTf)₂(H₂O)₂]²⁺ in the solid state (V = valinomycin, OTf = triflate). Along with the 1:2 complex, the solution phase 1:1 and 2:1 complexes have been characterised in acetonitrile by ¹H NMR and UV–Vis titration experiments. The molar absorptivity curves and binding equilibrium constants for these complexes have been determined by the global analysis of the UV–Vis titration data using the program SIVVU?.     

UV–vis,IR and 1H NMR spectroscopic studies and characterization of ionic-pair crystal violet–oxytetracycline

The present study shows the formation and characterization of the ionic-pair between the antibiotic oxytetracycline and the dye crystal violet in ammonia solution pH 9.0 ± 0.2 extracted into chloroform. The characterization was demonstrated using UV–vis spectrophotometry, ¹H NMR, measurement of relaxation times T₁ and IR spectroscopy, using a comparison between the signals of individual pure compounds with the signals with the mixture CV–OTC in different alkaline media. The formation of ionic-pair was also corroborated by new signals and chemical shifts. (2D) NMR spectroscopy experiments show that the interaction is electrostatic.     

Experimental (X-ray Diffraction,UV–Vis Spectroscopy) and DFT Studies of 1-Ethyl-3-methylquinoxaline-2-thione

Russian Journal of Physical Chemistry A - In this paper, we present the experimental and theoretical investigation of 1-ethyl-3-methylquinoxaline-2-thione, molecule exhibiting an important...     

Synthesis, X-ray crystallographic, and dynamic H NMR studies of crown-tetrathia[3.3.3.3]metacyclophanes—conformational control by cooperative intramolecular C-H?π interaction both in solid state and in solution

Crown-tetrathia[3.3.3.3]metacyclophanes 3a-c were synthesized via intermolcular coupling reaction in 22-30% yields. X-ray crystal analysis of 3b revealed that it adopted a perpendicular conformation (3b-B or 3b-C) in which two aromatic rings were inclined to be perpendicular to the opposite aromatic rings, driving two internal methyl groups into the π-cloud of the corresponding benzene rings. Furthermore, this perpendicular structural feature led to benzylic protons of thia-bridges being in close proximity to the adjacent aromatic rings. As a result, the induced upfield shifts for the two internal methyl protons and four benzylic protons were clearly observed in dynamic ¹H NMR spectra at low temperature, indicating that the intramolecular C-H?π interaction became increasingly important at low temperature. The energy barrier for inter-conversion between 3b-B and 3b-C was estimated to be 12.1 kcal mol⁻¹ by using a coalescence method. The total stabilization enthalpy of the C-H?π interactions was quantitatively calculated to be 7.9±0.8 kcal mol⁻¹ by the dynamic NMR spectroscopy. In contrast, 3a showed two non-interconvertible conformers at room temperature, which tended to interconvert at elevated temperature, however, many conformers co-existed at low temperature.     

Novel dioxorhenium complex with bis(3,5-dimethypyrazol-1-yl)methane ligand – Synthesis,spectroscopic characterization,X-ray structure and DFT calculations

The reactions of [ReOBr₃(PPh₃)₂] and [ReOBr₃(AsPh₃)₂] with bis(3,5-dimethypyrazol-1-yl)methane (bdmpzm) have been examined and novel dioxorhenium(V) complex [ReO₂(bdmpzm)₂]Br · HBr · 2H₂O has been obtained. The compound has been studied by IR, UV–Vis, ¹H NMR spectroscopy, magnetization measurements and X-ray crystallography. The electronic structure of the [ReO₂(bdmpzm)₂]⁺ cation has been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of [ReO₂(bdmpzm)₂]⁺ have been calculated with the TDDFT/PCM method, and the UV–Vis spectrum of [ReO₂(bdmpzm)₂]Br has been discussed on this basis.     

Synthesis,X-ray crystal structure,DFT calculations,spectroscopic characterization and redox behaviour of a rhodium(III) complex of an anthracene–pyridylhydrazone ligand

Transition Metal Chemistry - A pyridylhydrazone incorporating an anthracene moiety, designated as HLAnc, has been synthesized in order to examine its coordination behaviour towards rhodium(III)....     

Interaction between aspergillic acid and iron(III): A potentiometric,UV–Vis,H NMR and quantum chemical study

The complex formation equilibria of aspergillic acid with iron(III) were studied by potentiometric and spectrophotometric methods. The ligand was prepared by a biosynthetic route and its purity checked by MS and ¹H NMR spectroscopies. Some structural features of the ligand are discussed on the basis of NMR results. The iron(III) coordination model is compared with those of two other cyclic hydroxamates, 1-hydroxy-2-pyridinone and 1,4-dihydroxy-2-pyridinone, and its features are discussed on the basis of quantum chemical calculations.     

Temperature-dependent vibrational spectra of zinc(II) bis-(N,N′-diethyldithiocarbamate) in solid state and solution

The IR spectra of zinc(II) bis-(N,N′-diethyldithiocarbamate) in the solid state (at 20, 80 and 120°C) as well as in solution (20°C) have been recorded and discussed as to the changes in the zinc coordination sphere that may occur upon heating and dissolution. The decreased number of bands in the high-temperature and in the solution specta as compared with the room temperature solid state spectra has been explained by removal of the intermolecular contacts upon dissolution or thermal averaging in the high temperature solid state.     

Synthesis,X-ray, 1H-NMR and DFT analysis of the phthalimide–hydrazone probes as selective anion sensor

Two simple phthalimide–hydrazone probes with nitro groups were synthesised and characterised by NMR, FT-IR, HR-MS and single crystal X-ray crystallography. The synthesised receptors were evaluated for application in anion sensing. The receptors displayed strong, sensitive and selective colouration in the presence of cyanide ions by forming a stable complex with cyanide ion. The use of variable nitro groups helped in the elucidation of the mechanism of the complex formation. The ¹H NMR spectroscopy was used to support the mechanism of the complex formation. DFT methods were used to understand the stability of the complex with respect to the reactant. The absorbance data were also compared with the TD-DFT calculated excitation parameters. The experimental results were found to correlate well with the theoretical data.     

Synthesis,X-ray crystal structure,thermal and solution studies of a centrosymmetric metal–organic polymer based on proton transfer methodology

A 3-D metal–organic coordination polymer based on pyrazine-2,3-dicarboxylic acid (pzdcH₂) formulated as {[Mn(pzdc)(H₂O)₂] · 2H₂O} _n (1), was obtained by the treatment of MnCl₂ · 6H₂O with pzdcH₂, 8-hydroxy quinoline (8-HQ), and 2-amino-4-methyl pyridine (ampy). In this study, we describe the synthesis, elemental analysis, IR spectroscopy, TG analysis, and single X-ray diffraction. The X-ray single crystal structure reveals that the chemical environment around each Mn(II) is a distorted octahedral by participating one nitrogen, five oxygens from three (pzdc)^2? and two water molecules, O₅MnN. The centrosymmetric 1-D ladder-like structure of 1 is bridged by oxygens of (pzdc)^2?, and Mn–pzdc–Mn bonds are the rungs for our ladder structure. In the crystal structure, intermolecular O–H ··· O hydrogen bonds result in the formation of a supramolecular structure, effective for the stabilization of the structure. The thermal decomposition of 1 indicates that it is quite thermally stable. The protonation constants of ampy, 8-HQ and pzdcH₂ as the building blocks of proton transfer systems including pzdcH₂-ampy and pzdcH₂-8-HQ and the corresponding stability constants of these systems were determined by potentiometric study. The stoichiometry and stability constants of complexes of pzdcH₂-ampy and pzdcH₂-8-HQ with Mn²⁺ were investigated by this method in aqueous solution. The results obtained from solution study are comparable with the solid state results.     

Fractionation and characterization of gold nanoparticles in aqueous solution: asymmetric-flow field flow fractionation with MALS, DLS, and UV–Vis detection

Asymmetrical-flow field flow fractionation (AFFF) separates constituents based on hydrodynamic size and is emerging as a powerful tool for obtaining high-resolution information on the size, molecular weight, composition, and stability of nanoscale particles in liquid media. We employ a customized AFFF system combining on-line detectors for multi-angle light scattering, dynamic light scattering, and UV–Vis absorption. Our objective is to develop optimized measurement protocols for the characterization of gold nanoparticles (GNPs), which are widely utilized in biomedical research and other nanotechnology applications. Experimental conditions have been optimized by controlling key parameters, including injection volume and solids concentration, mobile phase composition, membrane type and pore size, and ratio of channel-to-cross-flow rates. Individual citrate-stabilized GNP components (nominally 10, 20, 30, 40, and 60 nm) and GNPs functionalized with polyethylene glycol were separated from multicomponent GNP mixtures by AFFF and subsequently characterized. We discuss the effects due to variations in measurement parameters and GNP surface modification on observed retention, recovery, and peak resolution.     

A novel two-dimensional silver(I) saccharinato coordination polymer constructed from weak Ag?C interactions: Synthesis, IR spectra and X-ray structure

A new dinuclear silver(I)-saccharinato (sac) complex with acetonitrile (MeCN), [Ag₂(sac)₂(MeCN)₂]_n has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. The silver(I) ions are doubly bridged by two sac ligands, leading to a short argentophilic contact of 2.9074(3) Å. Each silver(I) ion exhibits a square-planar coordination geometry including the Ag-Ag bonds. The individual dimeric molecules are extended into a two-dimensional layered structure by weak Ag?C_sac (η²) interactions of ca. 3.2 Å. These interactions were discussed and compared with those found in the first silver(I)-sac complex [Ag(sac)]_n.     

Crystal structure, IR and 1H NMR spectra of tetranitratobis μ-(2,4,6,8-tetraethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione-O,O′)]diethanolodicadmium

The crystal structure of [Cd₂(μ-BC)₂(NO₃)₄(EtOH)₂] (I), where BC is C₁₂H₂₂N₄O₂ (bicaret), has been determined. The crystals are composed of dimeric centrosymmetrical molecules. The cadmium coordination polyhedron is a trigonal bipyramid. Bicaret is a bidentate bridging ligand coordinated to the metal through two oxygens of the carbonyl groups. The IR and ¹H NMR spectra of I are studied and interpreted.     

Determination of the structure of quinolone-γ-cyclodextrin complexes and their binding constants by means of UV–Vis and <Superscript>1</Superscript>H NMR

The host–guest inclusion complex structure and binding ability of two different quinolones with γ-cyclodextrin (γ-CD) were investigated in solution by means of UV–Vis and ¹H NMR spectroscopy. Competition of oxolinic and nalidixic acid molecules for the γ-CD cavity was evaluated by determination of association constants. Both quinolones form 1:1 inclusion complexes, their binding constants at room temperature (25 °C) under acidic and basic conditions were calculated using Benesi–Hildebrand equation. The stability of the complexes was dependent on the structure of the quinolone. In general, the weaker binding constants were observed for oxolinic acid-γ-CD complexes (1616 and 1765 M^?1) and the larger binding constants were obtained for nalidixic acid-γ-CD complexes (3760 and 3840 M^?1). ¹H NMR studies in D₂O were performed to elucidate the structure of each inclusion complex, nalidixic acid molecule penetrates more deeply into the γ-CD cavity and an intermolecular hydrogen bond is formed. Knowledge about structure and relative stability of quinolone-γ-CD complexes will be useful for future applications of these antimicrobial agents in medicinal chemistry.