Search

The structural features of cobalt-based oxygen evolution catalysts are elucidated by combining high-field MAS NMR spectroscopy and DFT calculations. The superior photocatalytic activity of the heterogeneous system over its homogeneous counterpart is rationalised by the structural features. The higher activity is caused by a more favourable electron-withdrawing character of the framework. [ABSTRACT FROM AUTHOR]

An in‐depth analysis of the description of bonding within Cp′′′Ni‐cyclo‐P3 (Cp′′′=1,2,4‐tri‐tert‐butylcyclopentadienyl, [Ni]P3) employing X‐ray diffraction based multipolar modeling, density functional theory (DFT) as well as an "experimental wavefunction" obtained from X‐ray restrained wavefunction (XRW) fitting is presented. The results are compared to DFT calculations on white phosphorus – an isolobal analogue to [Ni]P3. A complementary bonding analysis shows insights into the reactivity of [Ni]P3. The isolobal principle is reflected in every aspect of our analysis and the employed methods seamlessly predict the differences in reactivity of [Ni]P3 and P4. Crystallographic modeling, solid‐state NMR, and DFT calculations describe the dynamic behavior of the cyclo‐P3 unit in the title molecule. [ABSTRACT FROM AUTHOR]

Two new ternary trielides Na7KTr4 (Tr=In, Tl) have been prepared by classical solid‐state reaction from the elements in tantalum ampoules. Both are isostructural to Na7RbTl4 and therefore crystallize in the orthorhombic space group Pbam, Pearson symbol oP96 (a=b=16.3283(2)/16.2860(6), c=11.3094(17)/11.2771(4), V=3015.25(8)/2991.07(18), Z=8, R1, wR2=0.0249, 0.0386/0.0447, 0.0608). The trielide subunit is built by two crystallographically independent [Tr4]8− tetrahedra. 23Na‐MAS‐Nuclear Magnetic Resonance (NMR) as well as EPR spectroscopy was employed to characterize the compounds further. DOS calculations showed a (pseudo) band gap at EF for both compounds. Dissolution experiments in liquid ammonia were carried out for the two alkali metal indides Na7KIn4 and Na2In according to the chemistry of group 14 and 15 Zintl anions. After evaporating the solvent, the remaining material was analyzed by powder X‐ray diffraction and proved the formation of NaIn and NaNH2. [ABSTRACT FROM AUTHOR]

Magnetic shielding depends on molecular structure and noncovalent interactions. This study shows that it is also measurably dependent on the electric field generated by surrounding molecules. This effect has been observed explicitly for 31P nucleus using the adduct under field approach. The results obtained indicate that the field strength experienced by molecules in crystals consisting of molecules with large dipole moments is similar to that in polar solvents. Therefore, magnetic shielding should explicitly depend on solvent polarity. It is important to note that this effect cannot be reproduced correctly within the polarizable continuum model approach. [ABSTRACT FROM AUTHOR]

Can the geometry of an acid-base complex in solution be reproduced in calculations using an implicit accounting for the solvent effect in the form of a macroscopic reaction field? The answer is, "Yes, it can." Is this field equal to the real electric field experienced by the complex in solution? The answer is, "No, it is not." How can the geometry be correct under wrong conditions? This question is answered using density functional theory modeling of geometric and NMR parameters of pyridine⋯HF⋯(HCF3)n adducts in the absence and presence of an external electric field. This adduct under field approach shows that the N⋯H distance is a function of the H–F distance whatever method is used to change the geometry of the latter. An explicit account for solute-solvent interactions is required to get a realistic value of the solvent reaction field. Besides that, this approach reveals how certain NMR parameters depend on the solvent reaction field, the solute-solvent interactions, and the geometry of the N⋯H–F hydrogen bond. For some of them, the obtained dependences are far from self-evident. [ABSTRACT FROM AUTHOR]

The effect of the local structure on the 31P NMR chemical shift tensor (CST) has been studied experimentally and simulated theoretically using the density functional theory gauge-independent-atomic-orbital approach. It has been shown that the dominating impact comes from a small number of noncovalent interactions between the phosphorus-containing group under question and the atoms of adjacent molecules. These interactions can be unambiguously identified using the Bader analysis of the electronic density. A robust and computationally effective approach designed to attribute a given experimental 31P CST to a certain local morphology has been elaborated. This approach can be useful in studies of surfaces, complex molecular systems, and amorphous materials. [ABSTRACT FROM AUTHOR]

An L-glutathione-functionalized silica adsorbent was applied in this study to remove malathion from aqueous media. This adsorbent has demonstrated an improved adsorption efficiency of malathion. The maximum uptake achieved was 130 mg g−1 at pH 8. Equilibrium was reached after about 90 min. A pseudo-second-order model best described the adsorption kinetics. The adsorption isotherms were best simulated by the Freundlich model. The functional groups are thermally stable up to about 150 °C. The elemental analysis results indicated high glutathione ligand densities. The results of this study show that the environmentally friendly L-glutathione functionalized silica is a promising candidate for the removal of malathion from water at the industrial level. [ABSTRACT FROM AUTHOR]

A simultaneously protonated and functionalized silicide cluster [NHCDippCu(η4‐Si9)H]2− was detected and characterized in liquid ammonia by NMR spectroscopy. Key NMR results were corroborated by theoretical calculations. 1H‐NMR line‐widths at variable temperatures revealed that proton hopping in the metalated complex [NHCDippCu(η4‐Si9)H]2− is less pronounced than in the non‐complexed silicide [HSi9]3−. Besides [HSi9]3− and [NHCDippCu(η4‐Si9)H]2− also the unprotonated analogous cluster [NHCDippCu(η4‐Si9)]3− was detected in solution. In addition, a new 29Si‐NMR signal was obtained in the course of 29Si‐NMR studies that we assigned to [NHCDippCu(η4‐Si9)]3−. The isolation of crystals of (K[2.2.2]‐crypt)2K0.48Rb3.52[NHCDippCu(η4‐Si9)]2 prove the availability of the non‐protonated NHCDippCu(η4‐Si9) fragment in solution. To the best of our knowledge the detection of [NHCDippCu(η4‐Si9)H]2− represents the first case of a protonated and coinage metalated group 14 Zintl cluster in solution so far. [ABSTRACT FROM AUTHOR]

Structural knowledge on ubiquitous lithium salts in solution and in the crystalline state is of paramount importance for our understanding of many chemical reactions and of the electrolyte behaviour in lithium ion batteries. A bulky bidentate Si-based ligand (6) was used to create simplified model systems suitable for correlating structures of LiCl and LiPF6 complexes in the solid-state and in solution by combining various experimental, spectroscopic, and computational methods. Solution studies were performed using 1H DOSY, multinuclear variable temperature NMR spectroscopy, and quantum chemical calculations. [Ph2Si(2-CH2Py)2·LiCl]2 (3) dissociates into a monomeric species (9) in THF. For [Ph2Si(2-CH2Py)2·LiPF6]2 (11), low temperature NMR studies revealed an unprecedented chiral coordination mode (12) in non-coordinating solvents. [ABSTRACT FROM AUTHOR]

In‐depth investigations of the long‐time known Zintl phase NaTl revealed a phase transition of tetragonal NaTl‐tI8 [I41/amd; a = 5.2268(9) Å, c = 7.539(1) Å, V = 205.97(9) Å3] to Zintl's cubic NaTl‐cF16 [Fd3m; a = 7.4697(6) Å, V = 416.79(5) Å3] between 351 and 355 K. This phase transformation was observed for NaTl prepared by two different synthetic routes including Zintl's original procedure. An excess of sodium applied during the synthesis in liquid ammonia also resulted in the formation of NaTl‐tI8. DSC measurements suggest a first order phase transition. In addition to in‐situ temperature dependent powder X‐ray diffraction experiments, DSC measurements and solid‐state NMR investigations, we also performed theoretical DOS and band structure calculations for the cubic and tetragonal phase, respectively. The results suggest Na‐Tl interactions in the second coordination sphere being responsible for the observed tetragonal distortion of Zintl's cubic NaTl. [ABSTRACT FROM AUTHOR]

Na SB 7 sb KTr SB 4 sb ( I Tr i =In, Tl) were characterized by single crystal X-ray structure analyses as well as SP 23 sp Na solid state NMR spectroscopy. Indium, Thallium, solid state 23Na NMR, Single Crystal, Liquid Ammonia Keywords: Indium; Thallium; solid state 23Na NMR; Single Crystal; Liquid Ammonia EN Indium Thallium solid state 23Na NMR Single Crystal Liquid Ammonia 1 1 1 11/07/23 20231102 NES 231102 The cover picture shows isolated [ I Tr i SB 4 sb ] SP 8- sp tetrahedra present in the unit cell of the new ternary trielides Na7KTr4 ( I Tr i =In, Tl). [Extracted from the article]

The study shows that combined NMR studies of enzyme and model systems can be easily employed for the localization of protons in critical enzyme hydrogen bonds. The results prove that the active site environment is better modeled by the proton donors in polar solvents than water.

The coordination chemistry of phosphinines (phosphabenzenes) has been intensively investigated over the last decades, but metal complexes of halophosphinines and related halide‐substituted phosphacyclohexadienyls have remained scarce. Here, we describe the synthesis of a series of complexes [Cp*Fe(1‐F‐PC5Ph3H2)] (2‐F, Cp* = C5Me5), [Cp*Fe(1‐Cl‐PC5Ph3H2)] (2‐Cl), [Cp*Fe(PC5Ph3H2)]Br (2‐Br) and [Cp*Fe(PC5Ph3H2)]I (2‐I), which were obtained by reacting the previously reported 2,4,6‐triphenylphosphinine iron complex [K([18]crown‐6)(thf)2] [Cp*Fe(PC5Ph3H2)] (1) with electrophilic halogenating agents. To the best of our knowledge, 2‐F and 2‐Cl are the first π‐coordinated λ3‐halophosphacyclohexadienyl complexes with covalent P–X bonds (X = halogen). In the solid state 2‐Br and 2‐I show ionic structures with [Cp*Fe(PC5Ph3H2)]+ cations and separated X– anions. Anion exchange of I– in 2‐I for [BArF4]– {ArF = 3,5‐(CF3)2C6H3} affords [Cp*Fe(PC5Ph3H2)][BArF4] (2‐[BArF4]), which also displays an ionic structure. These new complexes were further characterized by solid‐state and solution 31P NMR spectroscopy, UV/Vis spectroscopy, elemental analyses, electrical conductivity measurements in solution, and DFT calculations. The resulting data indicate that 2‐F retains its covalent P–F bond in THF, fluorobenzene, and acetonitrile solution, while the remaining 2‐X complexes containing heavier halogen atoms (X = Cl, Br, and I) apparently form ion pairs in such solvents. The full set of halide‐substituted phosphacyclohexadienyl iron complexes was synthesized. A thorough comparison of their molecular structures, spectroscopic and computational data indicates the presence of polarized phosphorus–halogen bonds. Depending on the halogen atom, the P–X bonds show a distinct tendency to dissociate in the solid state and in solution. [ABSTRACT FROM AUTHOR]

Anionic α‐diimine cobalt complexes, such as [K(thf)1.5{(DippBIAN)Co(η4‐cod)}] (1; Dipp=2,6‐diisopropylphenyl, cod=1,5‐cyclooctadiene), catalyze the dehydrogenation of several amine‐boranes. Based on the excellent catalytic properties, an especially effective transfer hydrogenation protocol for challenging olefins, imines, and N‐heteroarenes was developed. NH3BH3 was used as a dihydrogen surrogate, which transferred up to two equivalents of H2 per NH3BH3. Detailed spectroscopic and mechanistic studies are presented, which document the rate determination by acidic protons in the amine‐borane. A new class of cobalt catalysts with redox‐active bis(iminoacenaphthene) diimine (BIAN) ligands efficiently catalyzes transfer hydrogenation and dehydrogenation reactions of amine‐boranes. Alkenes, imines and quinolines were effectively reduced with ammonia borane (AB) as the dihydrogen surrogate. Moreover, AB can be used as an initiator for the hydrogenation of highly challenging trisubstituted olefins. [ABSTRACT FROM AUTHOR]

Although the chemistry of transition metal polyphosphide anions has attracted significant attention, there are few reports of studies in which such species have been synthesized directly from white phosphorus. [K(OEt2)2{Co(BIAN)(cod)}] ( 1, BIAN=1,2-bis(2,6-diisopropylphenylimino)acenaphthene, cod=1,5-cyclooctadiene), which is readily prepared by ligand exchange from [K(thf) x{Co(cod)2}], reacts with P4 to afford [{K(thf)}2{(BIAN)Co}2(μ-η4:η4-P4)] ( 2 a) in 61 % yield (isolated product). [{K(OEt2)}2{(BIAN)Co}2(μ-η4:η4-P4)] ( 2 b) and [K([18]crown-6)(MeCN)]2[{(BIAN)Co}2(μ-η4:η4-P4)] ( 2 c) were obtained by recrystallizing 2 a from diethyl ether and acetonitrile (and using [18]crown-6 in case of 2 c). Oxidation of 2 a with [Cp2Fe]BArF4 (one equivalent) and subsequent recrystallization of the product from different solvents gave [K(OEt2){(BIAN)Co}2(μ-η4:η4-P4)] ( 3 a) and [K(dme)4][{(BIAN)Co}2(μ-η4:η4-P4)] ( 3 b; dme=1,2-dimethoxyethane). Neutral [{(BIAN)Co}2(μ-η4:η4-P4)] ( 4) was obtained in moderate yield by oxidizing 2 a with two equivalents of [Cp2Fe]BArF4. The new complexes were characterized by NMR, EPR (in the case of 3 a), and UV/Vis spectroscopy, and elemental analysis. The molecular structures revealed by X-ray crystallography display planar cyclic or open-chain P44− units sandwiched between {(BIAN)Co} fragments. [ABSTRACT FROM AUTHOR]

The impact of the environment onto the geometry of hydrogen bonds can be critically important for the properties of the questioned molecular system. The paper reports on the design of calculation approaches capable to simulate the effect of aprotic polar solvents on the geometric and NMR parameters of intermolecular hydrogen bonds. A hydrogen fluoride and pyridine complex has been used as the main model system because the experimental estimates of these parameters are available for it. Specifically, F–H, F⋯N, and H–N distances, the values of 15N NMR shift, and spin–spin coupling constants 1J(19F1H), 1hJ(1H15N), and 2hJ(19F15N) have been analyzed. Calculation approaches based on the gas-phase and the Polarizable Continuum Model (PCM) approximations and their combinations with geometric constraints and additional noncovalent interactions have been probed. The main result of this work is that the effect of an aprotic polar solvent on the geometry of a proton–donor⋯H⋯proton–acceptor complex cannot be reproduced under the PCM approximation if no correction for solvent–solute interactions is made. These interactions can be implicitly accounted for using a simple computational protocol. [ABSTRACT FROM AUTHOR]

By using a combination of liquid and solid-state NMR spectroscopy, 15N-labeled 4-methylimidazole (4-MI) as a local probe of the environment has been studied: 1) in the polar, wet Freon CDF3/CDF2Cl down to 130 K, 2) in water at pH 12, and 3) in solid samples of the mutant H64A of human carbonic anhydrase II (HCA II). In the latter, the active-site His64 residue is replaced by alanine; the catalytic activity is, however, rescued by the presence of 4-MI. For the Freon solution, it is demonstrated that addition of water molecules not only catalyzes proton tautomerism but also lifts its quasidegeneracy. The possible hydrogen-bond clusters formed and the mechanism of the tautomerism are discussed. Information about the imidazole hydrogen-bond geometries is obtained by establishing a correlation between published 1H and 15N chemical shifts of the imidazole rings of histidines in proteins. This correlation is useful to distinguish histidines embedded in the interior of proteins and those at the surface, embedded in water. Moreover, evidence is obtained that the hydrogen-bond geometries of His64 in the active site of HCA II and of 4-MI in H64A HCA II are similar. Finally, the degeneracy of the rapid tautomerism of the neutral imidazole ring His64 reported by Shimahara et al. ( J. Biol. Chem.­ 2007, 282, 9646) can be explained with a wet, polar, nonaqueous active-site conformation in the inward conformation, similar to the properties of 4-MI in the Freon solution. The biological implications for the enzyme mechanism are discussed. [ABSTRACT FROM AUTHOR]

We have studied the hydrogen bond interactions of 15N labeled 4-methylpyridine (4-MP) with pentachlorophenol(PCP) inthe solid state and in polar solution using various NMR techniques.Previous spectroscopic, X-ray, and neutron crystallographic studiesshowed that the triclinic 1:1 complex (4-MPPCP) exhibits the strongestknown intermolecular OHN hydrogen bond in the solid state. By contrast,deuteration of the hydrogen bond gives rise to the formation of amonoclinic structure exhibiting a weaker hydrogen bond. By performingNMR experiments at different deuterium fractions and taking advantageof dipolar 1H–15N recoupling under combinedfast MAS and 1H decoupling, we provide an explanation ofthe origin of the isotopic polymorphism of 4-MPPCP and improve previouschemical shift correlations for OHN hydrogen bonds. Because of anharmonicground state vibrations, an ODN hydrogen bond in the triclinic formexhibits a shorter oxygen–hydron and a longer oxygen–nitrogendistance as compared to surrounding OHN hydrogen bonds, which alsoimplies a reduction of the local dipole moment. The dipole–dipoleinteraction between adjacent coupled OHN hydrogen bonds which determinesthe structure of triclinic 4-MPPCP is then reduced by deuteration,and other interactions become dominant, leading to the monoclinicform. Finally, the observation of stronger OHN hydrogen bonds by 1H NMR in polar solution as compared to the solid state isdiscussed. [ABSTRACT FROM AUTHOR]

The effect of the intramolecular H-bonding of the primary amide group on the spectral properties and reactivity of this group towards electrophiles has been studied in systematic rows of 1,2,5,6,7,8-hexahydro-7,7-dimethyl-2,5-dioxo-1-R-quinoline-3-carboxamides and 2-aryliminocoumarin-3-carboxamides using 1H and 15N NMR spectroscopy and the kinetics of model reactions. The upfield signal of the amide proton that is not intramolecularly H-bonded (Ha) depends on external factors such as solvent nature and concentration. At the same time, the downfield chemical shift of the Hb proton (bonded by the intramolecular hydrogen bond) depends mostly on the strength of the intramolecular H-bond, which is affected by such internal factor as electron nature of substituent R. The substituent's influence on the Hb proton's chemical shift is more effective in deuterochloroform medium than in DMSO- d6 where the intramolecular hydrogen bond is less stable. The value Δδ(H) = δ(Hb) − δ(Ha) is suggested as a simple comparative spectral index of the intramolecular hydrogen bond strength in these and similar compounds. By contrast, the effect of R on the 15N NMR chemical shift of the amide nitrogen has turned out to be too small to estimate changes of the electron density at the nitrogen. The effect of the intramolecular H-bond on the reactivity of the amide group is twofold. When the cleavage of the H-bond occurs on the rate limiting step it dramatically reduces the reaction rate. In the other case, the strengthening of the H-bond favors the reaction rate because of the increase of the electron density at the amide nitrogen. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using liquid-state NMR spectroscopy we have estimated the proton-donating ability of Zn-bound water in organometallic complexes designed as models for the active site of the metalloenzyme carbonic anhydrase (CA). This ability is important for the understanding of the enzyme reaction mechanism. The desired information was obtained by 1H and 15N NMR at 180 K of solutions of [TpPh,MeZnOH] [1, TpPh,Me = tris(2-methyl-4-phenylpyrazolyl)hydroborate] in CD2Cl2, in the absence and presence of the proton donors (C6F5)3BOH2 [aquatris(pentafluorophenyl)boron] and Col-H+ (2,4,6-trimethylpyridine-H+). Col-H+ forms a strong OHN hydrogen bond with 1, where the proton is located closer to nitrogen than to oxygen. (C6F5)3BOH2, which exhibits a pKa value of 1 in water, also forms a strong hydrogen bond with 1, where the proton is shifted slightly across the hydrogen-bond center toward the Zn-bound oxygen. Finally, a complex between Col and (C6F5)3BOH2 was identified, exhibiting a zwitterionic OHN hydrogen bond, where H is entirely shifted to nitrogen. The comparison with complexes of Col with carboxylic acids studied previously suggests that, surprisingly, the Zn-bound water exhibits in an aprotic environment a similar proton-donating ability as a carboxylic acid characterized in water by a pKa of 2.2 ± 0.6. This value is much smaller than the value of 9 found for [Zn(OH2)6]2+ in water and those between 5 and 8 reported for different forms of CA. Implications for the biological function of CA are discussed. [ABSTRACT FROM AUTHOR]

Hydrogen bond geometries and 1H NMR chemical shifts of OHO hydrogen-bonded systems have been analyzed using an improved valence bond order model. This model predicts that the heavy atom hydrogen bond coordinate q2 = r1 + r2 is a function of the proton coordinate q1 = 1/2(r1 - r2), where r1 and r2 represent the OH and the HO distances.In the first part, it is shown that this correlation reproduces published equilibrium geometries of the Zundel cation H5O2+ as well as those of water clusters in the gas phase and embedded in the fullerene C180. Using the example of the water hexamer, it is shown that changing the level of calculation shifts the calculated geometries along the correlation curve, but not away from the curve. In order to take quantum zero-point vibrational effects (QZPVE) into account, an empirical correction is proposed. It is shown that this correction properly describes the calculated classical and quantum hydrogen bond geometries of compressed ice as well as calculated geometric H/D isotope effects. The improved valence bond order model is used to analyze a large number of OHO hydrogen bond geometries contained in the Cambridge Structural Database.In the second part, a relation between the geometries and the 1H NMR chemical shieldings of OHO hydrogen bonded systems is established using the valence bond order model. GIAO calculations of the isolated symmetric Zundel cation where H is located in the hydrogen bond center show only a small dependence of the chemical shifts on the O..O distance. This result is rationalized in terms of neighbor group effects and deshielding in the naked proton. The consequence is that the 1H NMR chemical shifts are not much affected by QZPVE. Calculations on water clusters indicate that the influence of the chemical environment of the OHO hydrogen bonds on their 1H NMR chemical shifts is smaller for the strong hydrogen bond regime but large for the weak hydrogen bond regime. A simple chemical shift vs. q1 relation is then used to calculate the average chemical shifts of water clusters in the regime of fast hydrogen bond exchange between hydrogen bonded and free OH groups. It is shown that average chemical shifts of about 6 ppm are possible as the clusters considered exhibit a broad distribution of stronger and weaker hydrogen bonds. The implications for water in organic solvents and for liquid water are discussed, based on published data on the 1H chemical shift distribution in the latter. [ABSTRACT FROM AUTHOR]

Several charts related to hydrogen bond geometries are presented.

Keywords: Carbene ligands; Copper; Liquid ammonia; Silicides; Structure elucidation; Zintl phases EN Carbene ligands Copper Liquid ammonia Silicides Structure elucidation Zintl phases 3654 3654 1 09/29/21 20210924 NES 210924 B The Front Cover b shows a stylized representation of the compound [NHC SP Dipp sp Cu( SP 4 sp -Si SB 9 sb )H] SP 2- sp in a cocktail of the reagents and the solvent liquid ammonia at low temperatures. Carbene ligands, Copper, Liquid ammonia, Silicides, Structure elucidation, Zintl phases Front Cover: NMR-Spectroscopic Detection of an Elusive Protonated and Coinage Metalated Silicide [NHCDippCu( 4-Si9)H]2- in Solution (Eur. J. Inorg. [Extracted from the article]

The response of the geometric and NMR properties of molecular systems to an external electric field has been studied theoretically in a wide field range. It has been shown that this adduct under field approach can be used to model the geometric and spectral changes experienced by molecular systems in polar media if the system in question has one and only one bond, the polarizability of which significantly exceeds the polarizability of other bonds. If this requirement is met, then it becomes possible to model even extreme cases, for example, proton dissociation in hydrogen halides. This requirement is fulfilled for many complexes with one hydrogen bond. For such complexes, this approach can be used to facilitate a detailed analysis of spectral changes associated with geometric changes in the hydrogen bond. For example, in hydrogen-bonded complexes of isocyanide C≡15N-1H⋯X, 1J(15N1H) depends exclusively on the N-H distance, while δ(15N) is also slightly influenced by the nature of X. [ABSTRACT FROM AUTHOR]

The isotopically enriched cyanide anion, (13C≡15N)−, has a great potential as the NMR probe of non-covalent interactions. However, hydrogen cyanide is highly toxic and can decompose explosively. It is therefore desirable to be able to theoretically estimate any valuable results of certain experiments in advance in order to carry out experimental studies only for the most suitable molecular systems. We report the effect of hydrogen bonding on NMR properties of 15N≡13CH···X and 13C≡15NH···X hydrogen bonding complexes in solution, where X = 19F, 15N, and O=31P, calculated at the ωB97XD/def2tzvp and the polarizable continuum model (PCM) approximations. In many cases, the isotropic 13C and 15N chemical shieldings of the cyanide anion are not the most informative NMR properties of such complexes. Instead, the anisotropy of these chemical shieldings and the values of scalar coupling constants, including those across hydrogen bonds, can be used to characterize the geometry of such complexes in solids and solutions. 1J(15N13C) strongly correlates with the length of the N≡C bond. [ABSTRACT FROM AUTHOR]

This review discusses molecular adducts, whose composition allows a symmetric structure. Such adducts are popular model systems, as they are useful for analyzing the effect of structure on the property selected for study since they allow one to reduce the number of parameters. The main objectives of this discussion are to evaluate the influence of the surroundings on the symmetry of these adducts, steric hindrances within the adducts, competition between different noncovalent interactions responsible for stabilizing the adducts, and experimental methods that can be used to study the symmetry at different time scales. This review considers the following central binding units: hydrogen (proton), halogen (anion), metal (cation), water (hydrogen peroxide). [ABSTRACT FROM AUTHOR]

Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its 31P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this 31P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported. [ABSTRACT FROM AUTHOR]

An implicit account of the solvent effect can be carried out using traditional static quantum chemistry calculations by applying an external electric field to the studied molecular system. This approach allows one to distinguish between the effects of the macroscopic reaction field of the solvent and specific solute–solvent interactions. In this study, we report on the dependence of the simulation results on the use of the polarizable continuum approximation and on the importance of the solvent effect in nonpolar solvents. The latter was demonstrated using experimental data on tautomeric equilibria between the pyridone and hydroxypyridine forms of 2,6-di-tert-butyl-4-hydroxy-pyridine in cyclohexane and chloroform. [ABSTRACT FROM AUTHOR]

It was shown that solute-solvent interactions remarkably affect the geometry of acid-base complexes even if the active sites of these complexes are not accessible for solvent molecules. Chem. Chem. Phys. Chem. Chem. Phys. Chem. Chem. Phys. [Extracted from the article]

We used a range of computational techniques to reveal an increased histamine affinity for its H2 receptor upon deuteration, which was interpreted through altered hydrogen bonding interactions within the receptor and the aqueous environment preceding the binding. Molecular docking identified the area between third and fifth transmembrane α-helices as the likely binding pocket for several histamine poses, with the most favorable binding energy of −7.4 kcal mol−1 closely matching the experimental value of −5.9 kcal mol−1. The subsequent molecular dynamics simulation and MM-GBSA analysis recognized Asp98 as the most dominant residue, accounting for 40% of the total binding energy, established through a persistent hydrogen bonding with the histamine −NH3+ group, the latter further held in place through the N–H∙∙∙O hydrogen bonding with Tyr250. Unlike earlier literature proposals, the important role of Thr190 is not evident in hydrogen bonds through its −OH group, but rather in the C–H∙∙∙π contacts with the imidazole ring, while its former moiety is constantly engaged in the hydrogen bonding with Asp186. Lastly, quantum-chemical calculations within the receptor cluster model and utilizing the empirical quantization of the ionizable X–H bonds (X = N, O, S), supported the deuteration-induced affinity increase, with the calculated difference in the binding free energy of −0.85 kcal mol−1, being in excellent agreement with an experimental value of −0.75 kcal mol−1, thus confirming the relevance of hydrogen bonding for the H2 receptor activation. [ABSTRACT FROM AUTHOR]

The protonated perovskite-like titanate H2La2Ti3O10 has been used to produce organic-inorganic hybrids with simple organic molecules: methylamine, methanol, monoethanolamine, and n-butylamine. The optimal pathways for the preparation of such hybrids are summarized. Solid-state NMR, combined with thermal analysis, Raman, and IR spectroscopy, has been applied to determine the bonding type in the obtained organic-inorganic hybrids. It has been found that, in the methanolic hybrid, the organic residues are covalently bound to the inorganic matrix. In contrast, in the methylamine and n-butylamine hybrids, the organic molecules are intercalated into the inorganic matrix in cationic forms. The structure of the monoethanolamine hybrid is composite and includes both the covalently bound and intercalated organic species. [ABSTRACT FROM AUTHOR]