Synthesis,spatial structure and spectral properties of pyrylo‐4 (thio) squaraines variously substituted in cyclobutene moiety

Synthetic routes have been developed to a number of (thio) squaraine dyes containing the residues of CH‐acids at the central cyclobutene ring. The electronic and spatial structure as well as the chemical conversions and optical behaviour of the compounds obtained have been studied both theoretically and by X‐ray diffraction analysis, ¹H NMR and electronic spectroscopy. As shown, the electronic nature and sterical characteristics of the central ring substituents give rise to some general conformational features and crystal packing regularities and also govern the spectral position of the first π–π^* absorption band. The structure–property relationships established in the study provide guidance for the purposeful design of deeply coloured (thio) squaraines. Copyright © 2015 John Wiley & Sons, Ltd.     

Assignment of 13C Resonances in the Phencyclone-Norbornadiene Adduct Via 2D NMR. 13C Evidence for Hindered Rotation of Unsubstituted Bridgehead Phenyl Rings

¹³C NMR chemical shift assignments were obtained for the Diels-Alder adduct of phencyclone with norbornadiene in CD₂Cl₂ and in CDCl₃ solution. The ¹³C spectrum at 50.3 MHz, as well as the ¹H spectrum at 200.1 MHz, show evidence for hindered rotation of the two unsubstituted bridgehead phenyl rings of the adduct at ambient temperatures. In CD₂Cl₂ solution, all 19 of the unique ¹³C nuclei of this molecule give rise to individual ¹³C resonances. The ¹H assignments which were made earlier, together with one-bond and long-range 2D heteronuclear correlation experiments, allowed the assignment of all ¹³C chemical shifts in the molecule.     

Proton Dynamics in Letovicite, (NH4)3H(SO4)2: A H and N NMR Spectroscopic Study

The improper ferroelastic phase letovicite (NH₄)₃H(SO₄)₂ has been studied by ¹H MAS NMR as well as by static ¹⁴N NMR experiments in the temperature range of 296–425 K. The ¹H MAS NMR resonance from ammonium protons can be well distinguished from that of acidic protons. A third resonance appears just below the phase transition temperature which is due to the acidic protons in the paraelastic phase. The lowering of the second moment M₂ for the ammonium protons takes place in the same temperature range as the formation of domain boundaries, while the signals of the acidic protons suffer a line narrowing in the area of T_c. The static ¹⁴N NMR spectra confirm the temperature of the motional changes of the ammonium tetrahedra. Two-dimensional ¹H NOESY spectra indicate a chemical exchange between ammonium protons and the acidic protons of the paraphase.     

Synthesis,Properties and Spectroscopic Studies of Cobalt (II) and Cobalt (III) Complexes with Planar Dithioxamides

The complexes [Coⁱⁱⁱ(LH₂)₃]X₃ (LH₂ = dithiooxamide, N-methyldithiooxamide, N,N′-dimethyldithiooxamide; X = Cl, Br, l) and [CoⁱⁱL]n have been prepared. They were characterized by analyses, thermal techniques, magnetic susceptibilities and spectroscopic (ligand-field, ¹³C-NMR, FT-IR) methods. The vibrational analysis of the prepared complexes is given using NH/ND and CH₃/CD₃ isotopic substitutions. The neutral dithiooxamides exhibit a bidentate chelating S,S-coordination, while the doubly deprotonated dithiooxamido anions act as bis-bidentate bridging S,N/N,S-ligands giving trans polymeric structures. The Co(III) complexes are octahedral with Co^IIIS₆ coordination spheres. A square planar geometry around Co(II) is assigned for the polymeric compounds.     

Combined solid state NMR and ONIOM studies of reversible crystalline phase reaction for nickel coordination compounds

Ni(II) with bis(acetylacetone)ethylenediamine ligand forms complexes which crystallizes as semi-hydrate with C2/c space group in monoclinic system and anhydrous form with Pna2(1) space group in orthorhombic system. ¹³C and ¹⁵N CP/MAS experiments were employed for structural characterization of both forms and searching of process of reversible water exchange in the crystal lattice. Comparative analysis of ¹³C and ¹⁵N principal elements of chemical shift tensors for ligand and complexes showed the sensitivity of δ_ii elements both for complexation and phase reaction processes. Theoretical ¹³C and ¹⁵N NMR shielding parameters σ_ii were computed employing ONIOM approach and correlated with experimental δ_ii data. The applicability of ONIOM in structural analysis of coordination compounds (CC) is discussed.     

Tautomery and acid-base properties of some azoderivatives of benzoylacetone

The structural, tautomeric and acid-base properties of the new 1-phenyl-2-(2-hydroxy-3-sulfo-5-chlorophenylhydrazo)butane-1,3-dione (H₂L¹), 1-phenyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)butane-1,3-dione (H₂L²), 1-phenyl-2-(2-hydroxy-3-sulfo-5-nitrophenylhydrazo)butane-1,3-dione (H₂L³) and 1-phenyl-2-(2-hydroxy-4-nitrophenylhydrazo)butane-1,3-dione (H₂L⁴) were studied using IR, ¹H and ¹³C NMR spectroscopies and potentiometry. The study reveals that H₂L^1-4 and the known 1-phenyl-2-(2-hydroxyphenylhydrazo)butane-1,3-dione (H₂L⁵) exist in solution as a mixture of Z-enol-azo-II and hydrazo-III tautomeric forms and that an increase in the solvent polarity shifts the tautomeric balance to the enol-azo form. The thermodynamic parameters of the proton dissociation in H₂L^1-5 were determined showing that this process is unspontaneous, endothermic and entropically unfavorable.     

The Synthesis,Vibrational Spectra,Electronic Spectra,and Thermal Analysis of Some Mixed Complexes with Planar Dithiooxamides

Planar Pd(LH)₂ complexes (LH₂ = H₂N C S C S N H₂, CH₃HNCSCSNHCH₃) form mixed polymeric complexes with Ni(II), Cu(II), Zn(II) and Cd(II) in alcalic media, where the planar Pd(LH)₂ complexes act as tetradentates with N-coordination. The electronic spectra and thermal behaviour are discussed, a thorough investigation of the i.r. spectra is presented and special attention has been given to the H/D, CH₃/CD₃ and ⁵⁸Ni/⁶²Ni, ⁶³Cu/⁶⁵Cu and ⁶⁴Zn/⁶⁸Zn isotopic shifts.     

Experimental (UV,NMR, IR and Raman) and theoretical spectroscopic properties of 2-chloro-6-methylaniline

In this work, the experimental and theoretical UV, NMR and vibrational spectra of 2-chloro-6-methylaniline (2-Cl-6-MA, C₇H₈NCl) were studied. The ultraviolet absorption spectra of compound that dissolved in ethanol were examined in the range of 200–400 nm. The ¹H, ¹³C and DEPT NMR spectra of the compound were recorded. FT-IR and FT-Raman spectra of 2-Cl-6-MA in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies were found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the calculated NMR chemical shifts and absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Study on the Selectivity of Anion Receptors Based on Similar (thio)urea Fragments

Three new selective anion receptors containing the (thio)urea binding sites were developed, Indole-3-formaldehyde phenyl-semithiocarbazone, Indole-3-formaldehyde nitrophenyl-semithiocarbazone, and Indole-3-formaldehyde nitrophenyl-semicarbazone, nominated as receptors 1, 2 and 3, respectively. Receptor 1 shows high selective recognition for F^? only, while both receptor 2 and receptor 3 containing a p-nitro group show high selective recognition for AcO^?. The high selective recognition of these receptors to anions is further investigated by X-ray crystallography diffraction, UV-vis, fluorescence analyses and ¹H NMR. Furthermore, receptor 2 changes from yellow to orange, and receptor 3 darkens when acetate is added, providing a way of detection by ‘naked-eye’.     

A computational NICS and 13C NMR characterization of the substitution patterns of C70−2x(BN)x fullerenes (x=1–25)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C_70?2x(BN)_x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated ¹³C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. ¹³C Chemical shifts (δ_iso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from ?25.29 to ?8.80) demonstrate that all the substituted species are aromatic, but less than C₇₀ (?27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral ³He NMR chemical shifts.     

The Influence on NMR Parameters of Silicon Penta Coordination in Silatranes

¹H, ¹³C, ¹⁹F and ²⁹Si NMR chemical shifts and coupling constants for Si-substituted silatranes, XSi(OCH₂CH₂)₃N, and triethoxysilanes, XSi(OCH₂CH₃)₃, where X = H, CH₃, and F have been studied. Expansion of the coordination numbers of silicon and tin leads to similar changes in the NMR parameters.     

Spectral and Computational Studies on Benzil Mono-(2-Pyridyl)Hydrazone

In the present study, structural properties of Mono-(2-Pyridyl) Hydrazone were studied extensively utilizing density functional theory (DFT) employing B3LYP exchange correlation. The Fourier transform infrared (solid phase) was recorded. The vibrational frequencies in the ground state were calculated by using density functional method (B3LYP) with 6-31G* and 6-311G** as basis sets. The spectral studies revealed that the title compound exists in Keto form. Spectral techniques that we employed include ¹H and ¹³C NMR, electronic, thermal techniques. Correlation between experimental chemical shifts and GIAO/B3LYP/6-311G**-calculated isotropic shielding constants, δ_exp = a + bσ_calc, are reported. Good linear regressions between experimental and theoretical results for ¹H and ¹³C were obtained.     

Al Multiple-Quantum MAS NMR of Mechanically Treated Bayerite (α-Al(OH)3) and Silica Mixtures

Two-dimensional ²⁷Al multiple-quantum magic angle spinning (MQMAS) NMR experiments are used to study mixtures of bayerite (α-Al(OH)₃) with either silicic acid (SiO₂.nH₂O) or silica gel (SiO₂) that have been ground together for varying lengths of time. This mechanical treatment produces changes in the ²⁷Al MAS and MQMAS NMR spectra that correspond to the formation of new Al species. Mean values of the quadrupolar interaction (P_Q) and isotropic chemical shift (δ_CS) are extracted from the two-dimensional ²⁷Al NMR spectra for each of these species. The presence of significant distributions of both ²⁷Al quadrupolar and chemical shift parameters is demonstrated and the effect of grinding duration on the magnitudes of these distributions is discussed.     

Crystal structure,NMR spectroscopy,electrical properties of catena-poly[(bis-glycinium-k 2 O:O)-di-μ-thiocyanate- k 2 N:S; k 2 S:N -cadmium (II)]

The crystal structure, the ¹¹¹Cd and ¹³C NMR spectroscopy, and the complex impedance have been carried out on a new polymeric hybrid compound: [Cd(NH₃CH₂COO)₂(SCN)₂] _n . Crystal structure shows that in the title compound the cadmium atoms have a 2N2S2O-hexa-coordination sphere, exhibiting pseudo-octahedral geometry. The cadmium atoms are bridged by two thiocyanate ions generating 1D polymeric chains. ¹¹¹Cd and ¹³C MAS NMR spectroscopy show multiplets that result from ¹¹¹Cd, ¹⁴N and ¹³C, ¹⁴N spin–spin coupling, respectively. The AC impedance measurements were performed as a function of both frequency and temperature. The AC and DC electrical conduction have been studied. The activation energy associated with the bulk resistance determined from equivalent circuit was found close to that of the activation energy obtained from DC conductivity. The conduction mechanisms are attributed to the correlated barrier hopping model.     

H, C NMR and JCH coupling constants investigation of 4-Phenylpyridine: A combined experimental and theoretical study

Proton coupled and uncoupled ¹³C, ¹H, DEPT, COSY and HETCOR NMR spectra of 4-Phenylpyridine (4-Phpy) have been reported for the first time except for its ¹H NMR spectrum. In order to provide a precise structural elucidation for carbon atoms those have very close chemical shifts to each other, the magnitude of ⁿJ_CH (n=1,2,3) coupling constants of 4-Phpy (C₁₁H₉N) have also been investigated. ¹³C, ¹H NMR chemical shifts and ^1-3J_CH coupling constants of 4-Phpy have been calculated by means of B3LYP density functional method with 6-311++G(d,p) basis set. Moreover, the optimized parameters (bond lengths, bond and torsion angles) of 4-Phpy have been calculated with B3LYP at 6-31G(d) level in methanol (ε=32.63). Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

Determination of Reorientation Angles from Two-Dimensional Exchange Spectra of Powders in Radiospectroscopy

A method for transforming a 2D exchange spectrum into an orientation representation is proposed which is based on finding the reorientation probability as a function of angles. A procedure of evaluation and analysis of two-dimensional magnetic spectra of powders is described and a method for finding the asymmetry parameter from 2D exchange spectra is proposed. The capabilities of the method are illustrated for a model ³⁵Cl 2D nutation exchange NQR spectrum of chloral hydrate CCl₃CH(OH)₂ and an experimental ¹³C 2D exchange NMR spectrum of dimethylsulphone CH₃–SO₂–CH₃. The asymmetry parameter of the chemical shift tensor for this compound is determined.     

Structural Assignment of Stilbenethiols and Chalconethiols and Differentiation of Their Isomeric Derivatives by Means of 1H‐ and 13C‐NMR Spectroscopy

Abstract

The ¹H‐ and ¹³C‐NMR spectra of some substituted stilbenes and chalcones were assigned unambiguously on the basis of a combination of homo‐ (COSY) and heteronuclear (HETCOR) two‐dimensional methods, the chemical shifts, as well as spin‐coupling constants. The A_ik empirical parameters of the –O–C(S)–N(CH₃)₂, –S–C(O)–N(CH₃)₂, and –SH group were calculated to help predict the chemical shifts of substituted stilbenes, 4′‐nitrostilbenes, and chalcones. The ¹H‐ and ¹³C‐NMR spectra have been shown to be able to differentiate between the isomers of O‐stilbenyl (4, 5) and S‐stilbenyl N,N‐dimethylthiocarbamates (7, 8) as well as O‐chalconyl (6) and S‐chalconyl N,N‐dimethylthiocarbamates (9).     

O(1D)和CD4反应的准经典轨线

在新的全域势能面上, 用准经典轨线方法细致地研究了O(¹D)+CD₄多通道化学反应的动力学．这个势能面是用交换不变多项式方法基于MRC+Q/aug-cc-pVTZ从头算点拟合得到的．通过计算得到了产物OD+CD₃、D+CD₂OD/CD₃O和D₂+DCOD/D₂CO的分支比、平动能分布以及角度分布,结果显示理论与实验吻合得较好, 从而说明了这个反应的同位素取代效应很小． 研究表明,O(¹D)+CD₄反应是经过陷入的抽取机理发生的： 最初主要通过D原子的抽取,并不是之前人们认为的直接C-D键的插入形成CD3OD中间物后再进而解离成各个产物通道．     

a-C∶H(N)薄膜结构的X射线光电子能谱分析

采用直流-射频等离子增强化学汽相沉积技术制备a-C∶H(N)薄膜，用X射线光电子能谱研究了混合气体中N₂含量对薄膜成分与结构的影响.a-C∶H(N)薄膜中含氮量可达9.09%.对a-C∶H(N)薄膜的C1s和N1s结合能谱的分析表明a-C∶H(N)薄膜的结构是由C₃N₄相镶嵌在sp²键结合的CN_x基体中组成.其中C₃N₄相中N和C原子比接近4∶3，不随薄