Magnetic Shielding Tensors Research Articles

Quantum chemistry investigation of electronic structure and NMR spectral characteristics for fluorides of dialkylamidosulfoxylic acids and related compounds

The parent (H(2)N-S-F) and N,N-dialkyl-substituted fluorides of amidosulfoxylic acid (R(2)N-S-F, R=Me or R(2)N=Morph) as well as the related compounds X-S-F (X=CH(3), OH, F, SiH(3), PH(2), SH, Cl) have been investigated with quantum chemical calculations at the ab initio (MP2) level of approximation. The geometries, electronic structures, molecular orbital (MO) energies and NMR chemical shift values have been calculated to evaluate the role and extent of the polarization and delocalization effects in forming of the high-field fluorine NMR resonances within the series of interest. The deltaF magnitudes for all investigated fluorides of amidosulfoxylic acid as well as the deltaN value calculated for Me(2)N-S-F are in the good agreement with the (19)F and (14)N NMR chemical shift values measured experimentally. For the parent compounds, H(2)N-S-F and H(2)N-SO(2)-F, the orientation of principal axes of the magnetic shielding tensors and the corresponding principal sigma(ii) values along these axes have been qualitatively interpreted basing on the analysis of the MO interactions in the presence of the rotating magnetic field.

Structure of 3,4-dicarboxy-1-methylpyridinium chloride studied by X-ray diffraction, DFT calculations, NMR and FTIR spectra

The structure of 3,4-dicarboxy-1-methylpyridinium chloride (34DCMPCl) has been studied by X-ray diffraction, DFT calculations, NMR and FTIR spectra. The crystals are monoclinic, space group P2 1. Chloride anion links two 3,4-dicarboxy-1-methylpyridinium cations into infinite zigzag chains down [0 1 0] by the OH⋯Cl −⋯HO hydrogen bonds of 2.953(2) and 2.968(2) Å. Hydrogen bonds in single molecules optimised by the B3LYP/6-31G(d,p) approach depend on the environment. In vacuum ( 2 and 3) the hydrogen bonded proton is linked with chloride atom (Cl–H⋯O), while in DMSO ( 4) the structure is similar to that in the crystal (Cl⋯H–O). Linear correlations between the experimental 13C and 1H chemical shifts ( δ exp) of the investigated compound in DMSO-d 6 and the calculated GIAO/B3LYP/6-31G(d,p) magnetic isotropic shielding tensors ( σ calc) using the screening solvation model (COSMO), δ exp = a + bσ calc, are reported. The FTIR spectrum of the solid compound is consistent with the X-ray structure. The deformation absorptions in plane and out of plane, both in FTIR and second-derivative spectra (d 2), appear as two bands and confirm the OH⋯Cl −⋯HO hydrogen bonds formation.

Linear response calculations of molecular optical and magnetic properties using program RPAC: NMR shielding tensors of pyridine and n-azines

The theory of the linear response of a single-determinant wavefunction and the associated molecular properties is reviewed briefly, and the current status of the RPAC molecular properties program system is described. The program is capable of calculating electronic excitation energies and intensities and of various analyses of the nature of the excitations with the aid of localized molecular orbitals. In addition, nuclear magnetic shielding tensors can be computed and analyzed in a localized orbital framework. As an example of the program's present capabilities, we present calculations of the nuclear shielding tensors of a series of six-membered aromatic compounds containing one or more nitrogen atoms in the localized orbital-local origin (LORG) method, using extended basis sets. The properties of the shieldings are discussed with the aid of a novel scheme for visualization of tensorial properties.

Structure of 1-carboxymethylpyridinium-4-carboxylate inner salt studied by X-ray diffraction, DFT calculations, vibrational and NMR spectra

The structure of 1-carboxymethylpyridinium-4-carboxylate inner salt has been studied by X-ray diffraction, B3LYP calculations, FTIR, Raman and NMR spectroscopic techniques. The crystals are monoclinic, space group P2 1/ n. Each molecule is engaged in two short asymmetric O·H·O hydrogen bonds (2.449(2) and 2.481(2) Å) with two adjacent molecules through head-to-head and tail-to-tail connections. Structures of 10 linear and two cyclic most stable complexes have been optimized by the B3LYP level of theory and the results have been compared with the X-ray data. Energy stabilizations, Δ E = E complex − E components, caused by H-bond and electrostatic interactions between the opposite charged atoms (N + and O −) have been determined and analyzed. The FTIR spectrum shows a broad and intense absorption in the 1500–400 cm −1 region, typical of short hydrogen bonds. In the Raman spectrum the broad absorption is absent. Linear correlations between the experimental 13C NMR chemical shifts ( δ exp) in D 2O and the GIAO/B3LYP calculated magnetic isotropic shielding tensors ( σ cal), δ exp = a + b σ cal, are analyzed.

DABCO mono-betaine hydrate studied by X-ray diffraction, DFT calculations and spectroscopic methods

A new DABCO mono-betaine (1-carboxymethyl-1,4-diazabicyclo[2.2.2]octane inner salt) has been synthesized. It crystallizes as monohydrate in orthorhombic space group Pmn2 1. The DABCO mono-betaine and water molecules are located on a mirror plane. The water molecules link DABCO mono-betaine into linear chains through the H–O–H⋯OOC and H–O–H⋯N hydrogen bonds of 2.709(2) and 2.875(2) Å. The structure of the title compound optimized at B3LYP/6-31G(d,p) level of theory is consistent with X-ray diffraction. The absorption bands in the FTIR spectrum have been assigned. The calculated magnetic isotropic shielding tensors confirm the assignments of the 13C NMR resonance signals.

Crystal and molecular structure of quinuclidine betaine hydrochloride studied by X-ray diffraction, DFT, FTIR, and NMR methods

Quinuclidine betaine hydrochloride (1-carboxymethyl-1-azabicyclo[2.2.2]octane hydrochloride, QNBH·Cl) has been synthesized and characterized by X-ray diffraction, FTIR and NMR spectroscopy, and DFT calculations. QNBH·Cl crystallizes in orthorhombic space group Pnma. In the crystal the Cl − anion is engaged in a medium–strong COOH·Cl hydrogen bond of 2.921(2) Å, in which the acidic proton is closer the carboxylate group and additionally in some C–H···Cl contacts, stabilizing the crystal structure. The atoms of the quinuclidine betaine are located on a mirror plane. The structure of QNB·HCl optimized at the B3LYP/6-31G(d,p) level of theory is consistent with the X-ray structure, however the O···H–Cl hydrogen bond is somewhat shorter, 2.895 Å. The FTIR spectra of QNBH·Cl and QNBD·Cl have been measured and the bands have been assigned to vibrations of the hydrogen bond. The 1H and 13C NMR chemical shifts correlate linearly with the calculated magnetic isotropic shielding tensors.

Crystal structure of and solvent effect on tautomeric equilibrium in Schiff base derived from 2-hydroxy-1-naphthaldehyde and methylamine studied by X-ray diffraction, DFT, NMR and IR methods

The structure of the Schiff base derived from 2-hydroxy-1-naphthaldehyde and methylamine ( 1) has been studied by X-ray diffraction, B3LYP/6-31G(d,p) calculations, NMR and FTIR spectroscopy. The crystal is monoclinic, space group P2 1/c, with symmetry-independent two molecules forming a dimer ( 1) via two short intramolecular (2.592(2) and 2.579(2) Å) and two longer intermolecular (2.957(2) and 3.053(2) Å) N–H···O hydrogen bonds. The structures of dimer ( 2) and two monomers ( 3 and 4) have been analyzed by B3LYP/6-31G(d,p) level of theory. Tautomeric equilibrium due to the intramolecular hydrogen transfer between enol and ketol forms ( 4 ⇌ 3) has been studied in five solvents on the basis of 13C NMR chemical shifts and equilibrium constants, K eq, determined. The equilibrium constants, K eq, have been found to increase linearly with the solvent parameter, E T. Linear correlations have also been established between the experimental 1H and 13C NMR chemical shifts ( δ exp) of keto ( 3) and enol ( 4) units in five solvents and the GIAO/B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors ( σ calc) using COSMO screening solvation model, δ exp = a + bσ calc.

Study of N, N-dimethyl(carboethoxymethyl)-3-phthalimidopropylammonium chloride dihydrate by DFT calculations, NMR and FTIR spectroscopy

N, N-dimethyl(carboethoxymethyl)-3-phthalimidopropylammonium chloride dihydrate ( 1) and N, N-dimethyl(carboxymethyl)-3-phthalimidopropylammonium hydrochloride ( 3) have been obtained in reaction of N, N-dimethyl-3-phthalimidopropylamine with ethyl chloroacetate and chloroacetic acid, respectively. N, N-dimethyl(carboethoxymethyl)-3-phthalimido-propylammonium chloride dihydrate ( 1) has been characterized by FTIR and NMR spectroscopy. Moreover, for ( 1) and ( 3) B3LYP calculations have been carried out. The optimized bond lengths, bond angles and torsion angles calculated by B3LYP/6-31G(d,p) approach have been presented. Both FTIR and Raman spectra of ( 1) are consistent with the calculated structures in the gas phase. Correlations between the experimental 1H and 13C NMR chemical shifts ( δ exp) of investigated compound in D 2O, and the GIAO/B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors ( σ calc), δ exp = a + b σ calc, are reported. The assignments of the anharmonic experimental solid state vibrational frequencies of ( 1) based on the calculated B3LYP/6-31G(d,p) harmonic frequencies have been made. Linear correlations between the experimental 1H and 13C chemical shifts and the computed screening constants confirm the optimized geometry.

Spectroscopic and theoretical study of amlodipine besylate

In this work, a joint experimental (FT-IR, FT-Raman, NMR) and theoretical DFT study on 3-ethyl-5-methyl-2-(2-aminoethoxymethyl)-4-(2-chlorophenyl)-1,4-dihydro-6-methyl-3,5-pyridinedicarboxylate benzenesulphonate (amlodipine besylate) compound is reported. The experimental vibrational spectra have been assigned based on DFT calculations performed at B3LYP level of theory using the standard 6-31G(d) basis set and a uniform scaling of the calculated wave numbers. The mean deviation in reproducing the whole Raman and FT-IR spectra by B3LYP/6-31G(d) calculations is 7.7 and 6.0 cm −1, respectively. The experimental 1H NMR spectrum of amlodipine besylate was successfully reproduced by theoretical DFT calculations of the nuclear magnetic shielding tensors, using the GIAO method. The molecular electrostatic potential of the molecule has been calculated and used for predicting site candidates for electrophilic attack.

Crystal structure and spectroscopic properties of the 1:1 complex of pyridine betaine with p-hydroxybenzoic acid

Crystal structure of the 1:1 complex of pyridine betaine (PyB) with p-hydroxybenzoic acid (HBA) has been determined by X-ray diffraction. The crystals are monoclinic, space group P2 1/ c with the unit cell parameters a = 11.9009(4), b = 10.3283(3), c = 11.0616(4) Å and β = 104.252(4)°, Z = 4, R = 0.038. Both oxygen atoms of the carboxylate group of PyB are linked with the carboxylic and hydroxyl groups of HBA of the neighboring molecules, through two O–H⋯O hydrogen bonds of 2.589(1) and 2.588(2) Å, respectively. The PyB and HBA molecules are connected into infinite chains parallel to the x-axis. The FTIR spectrum of the solid complex is consistent with the X-ray results. 1H and 13C chemical shifts of the title complex in D 2O and DMSO-d 6 and the GIAO/B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors ( σ) using the screening solvation model (COSMO), δ exp = a + bσ, are reported. In the theoretically optimized structures of the complex investigated the O⋯O distances between PyB and HBA are not the same.

Effects of different GIAO and CSGT models and basis sets on 2-aryl-1,3,4-oxadiazole derivatives

The direct molecular structure implementations of the gage-including atomic orbital (GIAO), individual gages for atoms in molecules (IGAIM) and continuous set of gage transformations (CSGT) methods for calculating nuclear magnetic shielding tensors at both the Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6-31G(d), 6-311G(d), 6-31++G(d,p), 6-311++G(d,p), and 6-311++G(df,pd) basis sets are presented. Dependence on the 1H and 13C NMR chemical shifts on the choice of method and basis set have been investigated. Also, these chemical shifts of 2-aryl-1,3,4-oxadiazoles 5a–g have been performed related to dihedral angles (C4–C3–C2–O) of two conformers. The optimized molecular geometries and 1H and 13C chemical shift values of 2-aryl-1,3,4-oxadiazoles 5a–g in the ground state have been obtained. The linear correlation coefficients of 13C NMR chemical shifts for these molecules were given. The new nuclear magnetic shielding tensors of tetramethylsilane (TMS) were calculated. The data of 2-aryl-1,3,4-oxadiazole derivatives display significant molecular structure and NMR analysis. Also, these provide the basis for future design of efficient materials having the 1,3,4-oxadiazole core.

Solid-state 13C and 59Co NMR spectroscopy of 13C-methylcobalt(iii) complexes with amine ligands

Five octahedral Co(iii) cations, [trans-Co(en)(2)(X)((13)CH(3))](n+) where en = ethylenediamine, X = CN(-), N(3)(-), NH(3), NO(2)(-) or H(2)O and n = 1 or 2, as well as [Co(NH(3))(5)(13)CH(3)](2+), have been investigated by solid-state (13)C and (59)Co NMR spectroscopy. We show that the determination of the (59)Co nuclear quadrupolar parameters both directly via(59)Co NMR and indirectly via(13)C NMR provide complementary information that is unavailable if one investigates only one nucleus. Specifically, (1)J((59)Co,(13)C) and the orientation of the largest component of the EFG were determined via(13)C NMR spectroscopy, which also established the negative sign of C(Q)((59)Co). Cobalt-59 NMR spectroscopy was used to characterize the cobalt magnetic shielding tensor, to verify the magnitudes of C(Q)((59)Co) and to establish the value of eta(Q), which is difficult to determine indirectly. The measurements show that the EFG tensors are either axially symmetric or close to being so, but there is a wide range of C(Q) values, from -40 MHz for the complex with X = H(2)O to -105 MHz with X = CN(-). The Co chemical shift tensors are approximately axially symmetric with the spans, delta(11)-delta(33), ranging from 3700 to 5600 ppm for X = H(2)O and CN(-), respectively. The latter measurements also established the relative orientations of the Co EFG and chemical shift tensors. Density functional theory calculations of the (59)Co EFG and magnetic shielding tensors as well as of (1)J((59)Co,(13)C) for the NO(2)(-) and N(3)(-) complexes were undertaken. These calculations confirm the experimental observation that the sign of C(Q) is negative and that the largest component of the EFG is along the Co-methyl-carbon bond.

Application of multinuclear magnetic resonance and gauge-including projector-augmented-wave calculations to the study of solid group 13 chlorides

A series of four anhydrous group 13 chloride salts has been studied by (35/37)Cl solid-state NMR spectroscopy and complementary quantum chemical calculations. Due to the large (35/37)Cl quadrupolar interactions in these salts, a high magnetic field (21.1 T) and the variable-offset QCPMG technique was used to obtain full chlorine central transition (m = -1/2 <--> 1/2) NMR spectra. Analyses of the NMR spectra of the synthetically important Lewis acid trichlorides of aluminium, gallium, and indium, as well as gallium dichloride, allowed for characterisation of the chlorine electric field gradient (EFG) tensors and, in three cases, the chlorine chemical shift (CS) tensors. The quadrupolar interaction was found to dominate the central transition chlorine NMR spectrum in all cases, with chlorine-35 quadrupolar coupling constants (C(Q)) ranging in magnitude from 22.45 +/- 2.00 to 40.44 +/- 2.00 MHz, and the spectral breadths ranging from approximately 1.0 to 2.5 MHz. For the trichloride salt of gallium, it was confirmed that the terminal chlorine sites exhibit larger chlorine C(Q) values than do the bridging chlorines. The isotropic chemical shifts range from 150 +/- 100 to 375 +/- 100 ppm while the largest CS tensor span is 500 +/- 200 ppm, for InCl(3). The chlorine chemical shift was found to increase with increasing M-Cl distance in all cases. Quantum chemical calculations of the EFG and magnetic shielding tensors, performed using the gauge-including projector-augmented-wave (GIPAW) method as implemented in the CASTEP program, were found to be in excellent agreement with the experimentally determined values, reproducing C(Q)((35)Cl) to within 7% in all cases. The agreement between experiment and theory substantiates the accuracy of the NMR parameters. Solid-state NMR spectra of the cation species (aluminium-27, gallium-69/71 and indium-113/115) were also collected, and the EFG and CS parameters were determined in some cases. The study demonstrates the utility of multinuclear solid-state magnetic resonance studies of half-integer spin quadrupolar nuclei in ionic systems when the central transition is broadened greatly by the quadrupolar interaction, and in particular contributes to our understanding of the relationship between solid-state structure and chlorine NMR interaction tensors.

Photoinduced linkage isomerism of {RuNO}6 complexes with bioligands and related chelators

Five novel complexes containing the {RuNO}(6) fragment and the anions derived from l-histidine (l-his), rac-3-amino-alanine (rac-dap), kojic acid (koj), methyliminodiacetic acid (mida), and thiodiacetic acid (tda) have been synthesised and characterised by single-crystal X-ray diffraction analysis, mass spectrometry, spectroscopic methods (NMR, UV-vis, IR) and elemental analysis. In the irradiated complexes, [Ru(NO)Cl(2)(l-his)] (1), [Ru(NO)Cl(2)(rac-dap)] (2), K[Ru(NO)Cl(3)(koj)] (3), K[Ru(NO)Cl(2)(mida)].(1/2)H(2)O (4), and K[Ru(NO)Cl(2)(tda)].H(2)O (5), the existence of the photoinduced long-lived metastable isonitrosyl state S1 and/or the side-on-bonded S2 state were detected by differential scanning calorimetry (DSC) and/or IR spectroscopy. For all complexes 1-5 full geometry optimisation, frequency analysis and calculation of the isotropic magnetic shielding tensors have been conducted in the framework of DFT theory.

Probing solid iminobis(diorganophosphine chalcogenide) systems with multinuclear magnetic resonance

A 31P and 77Se solid-state NMR investigation of the iminobis(diorganophosphine chalcogenide) HN(R2PE)2 (R = Ph,iPr; E = O, S, Se) systems is presented. The NMR results are discussed in terms of the known HN(R2PE)2 structures available from X-ray crystallography. The phosphorus chemical shift tensors are found to be sensitive to the nature of the alkyl and chalcogen substituents. The nature of the R group also influences the selenium chemical shift tensors of HN(R2PSe)2 (R = Ph, iPr), which are shown to be sensitive to hydrogen bonding in the dimer structure of HN(Ph2PSe)2 and to the presence of disorder in the case of HN(iPr2PSe)2. Scalar relativistic ZORA DFT nuclear magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. A theoretical investigation into the effect of the E-P···P-E “torsion” angle on the phosphorus and selenium chemical shift tensors of a truncated HN(Me2PSe)2 system indicates that the electronic effect of the alkyl group on the respective nuclear magnetic shielding tensors are more important than the steric effect of the E-P···P-E torsion angle.Key words: iminobis(diorganophosphine chalcogenide), solid-state NMR, 31P NMR, 77Se NMR, ZORA DFT.

Synthesis, spectroscopy, computational study and prospective biological activity of two novel 1,3,2-diazaphospholidine-2,4,5-triones

The preparation of two new 1,3,2-diazaphospholidine-2,4,5-triones is reported. Thus, 2-chloro-1,3,2-diazaphospholidine-2,4,5-trione [ClP(O)(NHC(O)C(O)NH) ( I)] and 2-benzylamino-1,3,2-diazaphospholidine-2,4,5-trione [C 6H 5CH 2NHP(O)(NHC(O)C(O)NH) ( II)] have been synthesized by the reaction of POCl 3 with the corresponding carboxylic diamide salts. The characterization of the compound I was performed by multinuclear ( 1H, 13C, 31P) NMR and FTIR spectroscopies, elemental analysis and also mass spectrometry. Both compounds show two signals at room temperature in the low field region of the 1H NMR spectrum, which collapsed to a single peak when the temperature is increased. Dynamic NMR ( 1H DNMR) and quantum chemical studies were performed to gain insight from this conversion process. The free activation energies, calculated at the coalescence temperatures are 18.51 and 17.45 kcal/mol for compounds ( I) and ( II), respectively, which are associated with a tautomeric interconversion process, most likely between the lactam and lactim forms. The relative energy, molecular geometry and vibrational properties of several plausible tautomers were analyzed by using quantum chemical calculations at the HF/6-311G** and B3LYP/6-311++G** levels of the theory. The nuclear magnetic shielding tensors have been calculated for both tautomeric forms using the gauge independent atomic orbital (GIAO) method at the B3LYP/6-311++G(3df,2p) level of approximation. A biological activity prediction using the PASS software shows that compound ( I) can be characterized by a superb anti-HIV activity whereas compound ( II) is a very good antineoplastic.

Relativistic calculation of nuclear magnetic shielding tensor using the regular approximation to the normalized elimination of the small component. III. Introduction of gauge-including atomic orbitals and a finite-size nuclear model

The relativistic calculation of nuclear magnetic shielding tensors in hydrogen halides is performed using the second-order regular approximation to the normalized elimination of the small component (SORA-NESC) method with the inclusion of the perturbation terms from the metric operator. This computational scheme is denoted as SORA-Met. The SORA-Met calculation yields anisotropies, Delta sigma = sigma(parallel) - sigma(perpendicular), for the halogen nuclei in hydrogen halides that are too small. In the NESC theory, the small component of the spinor is combined to the large component via the operator sigma x piU/2c, in which pi = p + A, U is a nonunitary transformation operator, and c approximately = 137.036 a.u. is the velocity of light. The operator U depends on the vector potential A (i.e., the magnetic perturbations in the system) with the leading order c(-2) and the magnetic perturbation terms of U contribute to the Hamiltonian and metric operators of the system in the leading order c(-4). It is shown that the small Delta sigma for halogen nuclei found in our previous studies is related to the neglect of the U(0,1) perturbation operator of U, which is independent of the external magnetic field and of the first order with respect to the nuclear magnetic dipole moment. Introduction of gauge-including atomic orbitals and a finite-size nuclear model is also discussed.

ANALYTICAL TREATMENT OF NUCLEAR MAGNETIC SHIELDING TENSOR INTEGRALS OVER EXPONENTIAL-TYPE FUNCTIONS

The present work concerns the analytical and numerical development of three-center molecular integrals over Slater-type functions (STFs) and B functions of the second order involving [Formula: see text] in the operator. These integrals appear in the analytic expression of the nuclear magnetic shielding tensor. The basis set of STFs is used to represent atomic orbitals. These STFs are expressed in terms of B functions, which are better suited to apply the Fourier transform method thoroughly developed by Steinborn group. Analytic expressions are obtained for the integrals of the second order involved in nuclear magnetic resonance shielding tensor over B functions. These expressions turned out to be similar to those obtained for the usual molecular multi-center integrals. Consequently, the numerical evaluation of the integrals under consideration will benefit from the work previously done on the molecular multi-center integrals.

Hydrogen bonds in 1:1 complex of piperidine-3-carboxylic acid with salicylic acid

The 1:1 complex between the zwitterionic piperidinium-3-carboxylate (P3C) and salicylic acid (SAL), P3C·SAL, has been characterized by single crystal X-ray analysis, FTIR and NMR spectroscopy, and by DFT calculations. The crystals are orthorhombic, space group Pbca, with a = 11.6477(7), b = 9.1754(6), c = 23.5833(12) Å. An O H⋯O bridge (2.537(1) Å) links the SAL and P3C moieties. The proton in this H bond is located closer to the salicylic carboxylate group. In the P3C moiety, the piperidine ring adopts the chair conformation, and the carboxylate group is in the axial orientation and is stabilized by an intramolecular N + H⋯O hydrogen bond of 2.847(1) Å. In the crystal packing, two P3C·SAL units form a centrosymmetric dimer through a pair of intermolecular N + H⋯O bonds of 2.801(1) Å. The dimers form a zigzag chain linked via another N + H⋯O bond (2.799(1) Å). In the structures of the monomeric [P3C·SAL] and dimeric [(P3C·SAL) 2] species optimized by B3LYP/6-31G(d,p) calculations, both the inter- and intra-molecular hydrogen bonds are shorter than in the crystal. The FTIR spectrum shows a broad absorption in the 3100–2400 cm −1 region attributed to νNH and νOH vibrations. The broad absorption in the 1500–600 cm −1 region is attributed to the O H·O hydrogen bonds. The 1H and 13C NMR spectra have been analyzed to elucidate the structure of the P3C·SAL complex in solution. The GIAO magnetic isotropic shielding tensors have been used to predict the 1H and 13C chemical shifts in DMSO solution.

Accurate First-Principle Prediction of (29)Si and (17)O NMR Parameters in SiO2 Polymorphs: The Cases of Zeolites Sigma-2 and Ferrierite.

The magnetic shielding tensors of silica polymorphs have been investigated by means of quantum chemical calculations. Several levels of theory, from Hartree-Fock to the last generation of Density Functional Theory based approaches, have been tested on predicting (29)Si and (17)O isotropic and principal components of the chemical shift tensors together with (17)O quadrupolar coupling constants. The NMR parameters have been computed on all known silica systems, namely, α-quartz, α-cristobalite, coesite, Sigma-2, and ferrierite zeolites. Besides, cluster based approaches have been compared to a hybrid Quantum-Mechanics/Molecular-Mechanics (QM/MM) method, within the ONIOM scheme. The convergence of computed (17)O NMR parameters with respect to cluster size is found to be system-dependent. Excellent agreement between computed and experimental data has been found for (29)Si NMR parameters of the different Si sites of silica polymorphs and of Sigma-2 and ferrierite zeolites.