NMR Spectroscopic Properties Research Articles

Impact of crystal and molecular structure of three novel thiosulfonate crystals on their vibrational and NMR parameters

Due to antimicrobial potential of S-containing compounds, the current study explores experimentally the crystal and molecular structure of three new thiosulfonates at 100 K, notably S-ethyl 4-aminobenzene-1-sulfonothioate (1), S-ethyl 4-acetamidobenzene-1-sulfonothioate (2), and S-methyl 4-acetamidobenzene-1-sulfonothioate (3). Theoretical analysis between their molecular structure and vibrational IR, Raman, as well as NMR parameters is given. The details of -SO2-S- structural motif are analyzed theoretically using HOOH, HS-SH and H3CS-SCH3, as model molecules. The experimental structural parameters, as determined by low temperature X-ray diffraction method are accurately predicted using DFT-B3LYP combined with large and flexible aug-cc-pVTZ basis set. In case of C-S-S-C dihedral angle the crystal forces are responsible for larger difference with respect to isolated molecules, predicted in the gas phase. In addition, electronic properties of the title compounds are explored using theoretical calculations of their geometric and magnetic aromaticity indexes and substituent push-pull effect. The obtained results provide a deeper insight into their molecular structure and IR/Raman and NMR spectroscopic properties. Finally, these compounds could be directly used in future in vitro investigation of therapeutic potential of the studied and structurally similar compounds.

Synthesis, magnetic and NMR spectroscopic properties of the MAl5Pt3 series (M = Ca, Y, La-Nd, Sm-Er).

Following recent investigation in the ternary system Sr-Al-Pt led to the discovery of SrAl5Pt3 which crystallizes in the orthorhombic YNi5Si3 type (Pnma) structure. Interestingly, only two more aluminum representatives, CeAl5Pt3 and EuAl5Pt3, have been reported to adopt this structure type. Therefore, we decided to investigate the existence range of compounds adopting the YNi5Si3 type structure. Besides the already known Sr, Ce and Eu members, the series could be extended to Ca, Y and La-Nd as well as Sm-Er. All compounds were synthesized from the elements and characterized by powder X-ray diffraction. While for CaAl5Pt3 and LaAl5Pt3 also the respective M2Al16Pt9 members were observed, the other compounds could be obtained either as X-ray pure materials or with small amounts of Al3Pt2 as a side phase. The structure of ErAl5Pt3 could be refined from single crystal data, verifying that also the small rare-earth elements adopt the YNi5Si3 type structure. Selected members of the series were furthermore characterized by magnetization and susceptibility measurements. Since YAl5Pt3 could be obtained as a phase pure material and exhibits no paramagnetic behaviour it was investigated by 27Al MAS NMR investigations. Also, XPS measurements were conducted on this compound to gain an insight into the charge distribution. Finally, quantum-chemical calculations supported the NMR measurements and gave an insight into the chemical bonding and the charge distribution.

Triphosphiranes as phosphinidene-transfer agents - synthesis of regular and chelating NHC phosphinidene adducts.

In this contribution we describe the general use of aryl-substituted triphosphiranes (Ar3P3; Ar = Mes, Dip, Tip) as phosphinidene transfer reagents towards N-heterocyclic carbenes (NHCs) to give a library of twelve N-heterocyclic carbene phosphinidene adducts of the type ArPNHC (NHCPs), in which the NHCs have varying steric profiles, allowing a systematic evaluation of their structural and NMR-spectroscopic properties. In the next series of experiments we utilized 1,3- and 1,4-phenylene bridged bis-NHCs to access a new class of chelating bis(NHCP)s, of which three derivatives could be structurally characterized. The 1,4-phenylene derivatives were shown to be susceptible to P-CNHC bond cleavage when irradiated with an LED (396 nm), providing a rare example of phosphinidene release from NHCPs. The coordination chemistry of 1,3-phenylene bridged bis(NHCP)s towards GeCl2(dioxane) and GaI3 was investigated and revealed the formation of ion-separated cationic complexes, with significant charge transfer from the ligand to the metal center according to NBO analyses.

Poly-pnictogen bonding: trapping halide ions by a tetradentate antimony(iii) Lewis acid.

A highly halide affine, tetradentate pnictogen-bonding host-system based on the syn-photodimer of 1,8-diethynylanthracene was synthesized by a selective tin-antimony exchange reaction. The host carries four C[triple bond, length as m-dash]C-Sb(C2F5)2 units and has been investigated regarding its ability to act as a Lewis acidic host component for the cooperative trapping of halide ions (F-, Cl-, Br-, I-). The chelating effect makes this host-system superior to its bidentate derivative in competition experiments. It represents a charge-reversed crown-4 and has the ability to dissolve otherwise poorly soluble salts like tetra-methyl-ammonium chloride. Its NMR-spectroscopic properties make it a potential probe for halide ions in solution. Insights into the structural properties of the halide adducts by X-ray diffraction and computational methods (DFT, QTAIM, IQA) reveal a complex interplay of attractive pnictogen bonding interactions and Coulomb repulsion.

Crystal structure, IR and NMR spectra of (E)-2‑methoxy-4-(2-morpholinovinyl)phenol molecule and its DFT calculations

In this study; molecular structure, IR and NMR spectroscopic properties of (E)-2‑methoxy-4-(2-morpholinovinyl)phenol are investigated both experimentally and theoretically for the first time. The structural characterization of the compound was carried out by X-ray diffraction technique. The bond lengths, bond angles and dihedral angles of the compound were optimized using DFT with the B3LYP 6–311G(dp) base set. Using the optimized results, the infrared vibration frequencies and intensities of the compound as well as the 1H and 13C chemical shift values in the NMR spectrum were calculated with the B3LYP 6–311G(dp) basis set. In addition, the potential energy distributions (PED) of the structure were calculated to determine some characteristic vibrational frequencies of the compound. It is found that the theoretically calculated data support the experimental results. As a result, there is a good agreement between the experimentally determined structural parameters, vibrational frequencies, chemical shifts and theoretically calculated data of the compound.

Bonding situations in tricoordinated beryllium phenyl complexes.

The bonding situation in the tricoordinated beryllium phenyl complexes [BePh3 ]- , [(pyridine)BePh2 ] and [(trimethylsilyl-N-heterocyclic imine)BePh2 ] is investigated experimentally and computationally. Comparison of the NMR spectroscopic properties of these complexes and of their structural parameters, which were determined by single crystal X-ray diffraction experiments, indicates the presence of π-interactions. Topology analysis of the electron density reveals elliptical electron density distributions at the bond critical points and the double bond character of the beryllium-element bonds is verified by energy decomposition analysis with the combination of natural orbital for chemical valence. The present beryllium-element bonds are highly polarized and the ligands around the central atom have a strong influence on the degree of π-delocalization. These results are compared to related triarylboranes.

β-Trioxopyrrocorphins: pyrrocorphins of graded aromaticity.

Octaethyltrioxopyrrocorphins unexpectedly show macrocycle-aromatic properties, even though they contain the macrocyclic π-system of the non-aromatic pyrrocorphins (hexahydroporphyrins). Two of the four possible triketone regioisomers were first reported in 1969 by one-pot oxidation of octaethylporphyrin but remained essentially unexplored since. We detail here the targeted preparation of the remaining two triketone isomers and the optical and NMR spectroscopic properties of all isomers. All four regioisomers possess unique electronic properties, including broadly varying degrees of diatropicity that were experimentally determined using 1H NMR spectroscopy and computationally verified. Structural patterns modulating the aromaticity were recognized. These differences highlight the regioisomerically differentiated influences of the three β-oxo-functionalities. We also present the solid state structure of the two most common isomers (in their free base form or as zinc complexes), allowing further conclusions to be made about the resonance structures present in these triketones. Remarkably, also, the halochromic properties of the triketones differ sharply from those of regular (hydro)porphyrins, providing further support for the proposed 16-membered, 18 π-electron aromatic ring-current. The work conceptually expands the understanding of tris-modified hydroporphyrinoid analogues and the factors that enable and control porphyrinoid aromaticity.

NMR Parameters of Imidazolium Ionic Liquids as Indicators of Their State and Properties in Aqueous Solutions

Seven 1-methylimidazolium-based ionic liquids (ILs) and their aqueous solutions were systematically investigated in order to explore how the NMR spectroscopic properties (chemical shifts, spin–spin coupling constants) are connected or correlated with several physical and chemical properties (density, viscosity, water content, etc.) of ILs and their aqueous mixtures. 1H and 13C NMR chemical shifts of ILs vary markedly depending on different anions, alkyl chain length, and water content. Addition of water affected the NMR parameters in various manners, altering several of them significantly, while others did not change distinctly. Dissimilar behavior of NMR parameters in various solvents at various concentrations allows one to conclude that they reflect several contributions from different properties of ILs and can be used for deep structural investigations.

Phenylvinylidene RePt Complexes Containing Diphenylphosphine Ligands at the Platinum Atom: Synthesis, IR, NMR Spectroscopic and Electrochemical Properties

The μ-phenylvinylidene complexes Cp(CO)2RePt(μ-C=CHPh)(PPh2H)(L) [L = PPh3 (1), P(OPri)3 (2)] were synthesized for the first time. Their IR, NMR spectroscopic and redox properties were studied. Based on IR, NMR spectroscopic data their molecular structures were proposed. The pathways of redox-reactions of the complexes were determined

Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

Reaction of N‐alkylated imidazoles with 2‐chloro‐4‐quinazolinone gave mesomeric betaines, 2‐(1‐alkyl‐1H‐imidazolium‐3‐yl)quinazolin‐4‐olates, for which three tautomeric forms of N‐heterocyclic carbenes (NHCs) can be formulated, in addition to an anionic NHC after deprotonation. The NHC tautomers were trapped with sulfur, selenium, triethylborane, and triphenylborane as thiones, selenones and borane adducts, respectively. We obtained two isomers of the cyclic borane adducts, diazaboroloquinazolinones with [1,5‐a] and [5,1‐b]‐type fusion between the quinazolinone and the diazaborole rings. They correspond to two different NHC tautomers and to the anionic NHC derived thereof. The third NHC tautomer was trapped as a non‐cyclic adduct with tris(pentafluorophenyl)borane by coordination to the quinazoline oxygen atom. 2D 1H‐15N HMBC experiments of 15N‐labeled quinazolinone fragments, quantitative measurements of long‐range 1H‐15N coupling constants (JHN), and five X‐ray single crystal analyses have been carried out for the structure elucidations and to gain insight into the NMR spectroscopic properties of these compounds.

Theoretical study of the stability and NMR spectroscopic properties of vanadium(V) complexes

Several vanadium(V) complexes have been investigated as possible antidiabetic and anticancer therapeutic agents. Among these, vanadium(V) complexes linked to tridentate ONO Schiff bases stand out for their potential in the treatment for cancer. However, further studies are necessary in order to learn about their specific action at the cellular level. We investigate structural and spectroscopic properties of these particular complexes, which are formed by a Schiff base linked to a [VO2]+ ion that contains different functional groups. Molecular structure optimizations of these vanadium-containing complexes were performed by the ONIOM (QM1:QM2) method, where the high layer (complexes) were described by density functional theory methods whereas the low layer (eight water molecules) were described by the HF approach. Various solvation models were utilized; however, the introduction of both implicit (using a solvation model based on density, SMD) and explicit (eight water molecules) solvation improves the stability of the systems. Interestingly, we found that the location of the explicit water molecules in the different octahydrated vanadium complexes was conserved surrounding the oxo-vanadate moiety. A detailed analysis of the chemical shift (δ) values for 1H, 13C and 51V is presented based on the ONIOM optimized geometries using the gauge-independent atomic orbital methodology. For obtaining accurately chemical shifts, the complete basis set using the correlation-consistent Dunning basis sets from double-ξ to quadruple-ξ and the Ahlrichs basis set were utilized. The results from the methodology presented here are consistent with those reported experimentally for 1H. Again, the inclusion of explicit water molecules in the inner solvation shell during the calculation of the chemical shifts was crucial. The analysis of solvation energies also indicates the relevance of including explicit water molecules as the main stabilization factor suggesting the central role of intermolecular interaction in the stability of the metallic complexes. From this analysis, a possible vanadium complex candidate for further evaluation in the cellular environment is suggested. This work not only provides evidence of a suitable methodology for studying the structural and spectroscopic properties of vanadium complexes but also highlights the relevance of explicitly including water molecules in their inner shell.

Nanosized Layered TOT Magnesium Silicates: Equilibrium Morphologies and Surface Speciation, a Computational and Experimental Study

The morphology, surface speciation, NMR, and IR spectroscopic properties of nanosized layered magnesium silicate isostructural to talc at equilibrium in an aqueous environment were computed from fi...

On the hydrophobic effect in water–alcohol mixtures

Binary mixtures of water and various alcohols (W/ROH) were characterized in the light of the pure solvent scales, using suitable probe/homomorph couples. Various thermodynamic properties (viz. vapour pressure and enthalpy of mixing), viscosity, and the IR and NMR spectroscopic properties of the mixtures, as well as the solvatochromic behaviour on UV [NA, ENB, ET(30), and Z] and NMR probes (124Xe) are described in terms of microscopic properties like polarity, acidity, and basicity, and the descriptions examined in relation to a potential physical significance. Finally, the hydrophobic effect is discussed in the light of the results.

Theoretical analysis and modeling of the electrostatic responses of the vibrational and NMR spectroscopic properties of the cyanide anion

The nature of the electrostatic responses of the vibrational and NMR spectroscopic properties is analyzed theoretically for the cyanide anion and the cyanide ligand to the heme. It is shown that the dependence of the CN stretching frequency on the applied electric field (the origin of the Stark tuning rate) is sufficiently large and linear, suggesting that the cyanide anion and ligand are good probes of the electrostatic situation around them. On the basis of the electron density analysis, it is clarified that the behavior of electrons induced by molecular vibrations plays an important role in this response. Electrostatic interaction models that employ both the vector and scalar components on atomic sites are constructed to consistently explain the changes in the spectroscopic properties induced by uniform electric field and by hydrogen-bond formation with water. It is shown that the vibrational and NMR spectroscopic properties are affected differently by the electric fields and electrostatic potentials on the atomic sites, suggesting that these probes play mutually complementary roles in elucidating the electrostatic situations around the CN group.

Influence of Solvent and Electric Field on the Structure and IR, 31P NMR Spectroscopic Properties of a Titanocene–Benzyne Complex

The effect of solvent on the structural, frontier orbital energies, global density-based descriptors, vibrational frequencies, and 31P NMR chemical shifts was examined for the syn-Cp2Ti(η2-C6H4-2-OMe)(PMe3) complex by the self-consistent reaction field theory (SCRF) based on the polarizable continuum model (PCM). The studied spectroscopic parameters were correlated with the Kirkwood–Bauer–Magat (KBM) equation. Also, the response of the global density-based descriptors (chemical potential and hardness) in the presence of external electric field was studied. EDA, QTAIM, ELF, LOL, and NBO analyses were used for illustration of the Ti–C bond in this complex.

NMR spectroscopic properties of furo[2′,3′:4,5]pyrrolo[1,2-d][1,2,4]triazine derivatives

Abstract The 1H and 13C NMR spectroscopic properties of a series of furo[2′,3′:4,5]pyrrolo[1,2-d][1,2,4]triazin-8(7H)-ones and -thiones were investigated. The influence of various electron donating as well as electron withdrawing substituents at C-5 or N-7 on 1H NMR chemical shifts as well as 13C chemical shifts at C8 were observed. The 5-chloromethyl group had a little influence on the chemical shift of H-7 proton and the 8-thione group causes deshielding of H-7 as well as H-5 protons in comparison with the C-8 carbonyl group.

Spectroscopic investigations (FT-IR, UV, 1H and 13C NMR) and DFT/TD-DFT calculations of potential analgesic drug 2-[2-(dimethylamino)ethyl]-6-methoxy-4-(pyridin-2-yl)-1(2H)-phthalazinone

The theoretical molecular geometry and the IR, UV, 1H and 13C NMR spectroscopic properties of 2-[2-(dimethylamino)ethyl]-6-methoxy-4-(pyridin-2-yl)-1(2H)-phthalazinone with the previously demonstrated in vivo analgesic activity were characterized. The conformational analysis, performed using the molecular mechanics method with the General AMBER Force Field (GAFF) and the Density Functional Theory (DFT) approach with the B3LYP hybrid functional and the 6–31 + g(d) basis sets, allowed to determine the most stable rotamer. The theoretical molecular geometry of this conformer was then calculated at the B3LYP/6–311++g(d,p) level of theory, and its phthalazinone core was compared with the experimental geometry of 1(2H)-phthalazinone. The calculated vibrational frequencies and the potential energy distribution enabled to assign the theoretical vibrational modes to the experimental FT-IR bands. The UV spectrum calculated with the Time-Dependent Density Functional Theory (TD-DFT) method in methanol identified the main electronic transitions and their character. 1H and 13C NMR chemical shifts simulated by the Gauge-Independent Atomic Orbital (GIAO) method in chloroform confirmed the previous assignment of the experimental resonance signals. The stability of the molecule was considered taking into account the hyperconjugation and electron density delocalization effects evaluated by the Natural Bond Orbital (NBO) method. The calculated spatial distribution of molecular electrostatic potential made possible to estimate the regions with nucleophilic and electrophilic properties. The results of the potentiodynamic polarization measurements were also indicated the corrosion inhibition activity of the title compound on 100Cr6 bearing steel in 1 mol dm−3 HCl solution.

Excimer formation from particially overlapped anthracene dimer based on saddle-shaped cyclooctatetrathiophene as spacer

With “saddle” shaped tetra[3,4-Thienylene] (TT) as a rigid 3D spacer, three anthryl substituted TT compounds, 1-(anthracen-9-yl)[3,3′-bithiophene] (TTA-1), 1,7-di(anthracen-9-yl)-[3,3′-bithiophene] (TTA-2) and 1,12-di(anthracen-9-yl)[3,3′-bithiophene] (TTA-3) were designed and synthesized. Their physical behaviors including NMR spectra, crystal structures and spectroscopic properties were studied. Due to the steric hindrance from TT moiety to avoid the dimer formation between molecules, TTA-1 and TTA-2 show monomer anthracene emission both in solution and rigid state, and a mixture of monomer and excimer emission in aggregation state. Bearing two ipsilateral anthracene moieties in molecule, TTA-3 gives a twisted and end-overlapped dimer in the ground state, and shows excimer emission only in solution, aggregation state and rigid state. In addition, a model compound, 2,2′-di(anthracen-9-yl)-5,5′-di(trimethylsilyl)-[3,3′-bithiophene] (BTA) was prepared, which shows monomer emission in both solution and rigid state, but gives excimer emission in the aggregation due to its extended conformation in solution and intermolecular dimer arrangement in its crystal and aggregation state.

Intramolecular hydrogen bonding in conformationally semi-rigid α-acylmethane derivatives: a theoretical NMR study.

Conformational mobility is a core property of organic compounds, and conformational analysis has become a pervasive tool for synthetic design. In this work, we present experimental and computational (employing Density Functional Theory) evidence for unusual intramolecular hydrogen bonding interactions in a series of α-acylmethane derivatives, as well as a discussion of the consequences thereof for their NMR spectroscopic properties.

Tin-Free Direct C-H Arylation Polymerization for High Photovoltaic Efficiency Conjugated Copolymers.

A new and highly regioselective direct C-H arylation polymerization (DARP) methodology enables the reproducible and sustainable synthesis of high-performance π-conjugated photovoltaic copolymers. Unlike traditional Stille polycondensation methods for producing photovoltaic copolymers, this DARP protocol eliminates the need for environmentally harmful, toxic organotin compounds. This DARP protocol employs low loadings of commercially available catalyst components, Pd2(dba)3·CHCl3 (0.5 mol%) and P(2-MeOPh)3 (2 mol%), sterically tuned carboxylic acid additives, and an environmentally friendly solvent, 2-methyltetrahydrofuran. Using this DARP protocol, several representative copolymers are synthesized in excellent yields and high molecular masses. The DARP-derived copolymers are benchmarked versus Stille-derived counterparts by close comparison of optical, NMR spectroscopic, and electrochemical properties, all of which indicate great chemical similarity and no significant detectable structural defects in the DARP copolymers. The DARP- and Stille-derived copolymer and fullerene blend microstructural properties and morphologies are characterized with AFM, TEM, and XRD and are found to be virtually indistinguishable. Likewise, the charge generation, recombination, and transport characteristics of the fullerene blend films are found to be identical. For the first time, polymer solar cells fabricated using DARP-derived copolymers exhibit solar cell performances rivalling or exceeding those achieved with Stille-derived materials. For the DARP copolymer PBDTT-FTTE, the power conversion efficiency of 8.4% is a record for a DARP copolymer.