Relativistic Density Functional NMR Tensors Analyzed with Spin-free Localized Molecular Orbitals

The implementation of fast relativistic methods based on density functional theory, in conjunction with localized molecular orbital (LMO) based analysis, allows straightforward interpretations of NMR parameters in terms of contributions from core shells, lone pairs, and bonds, for compounds containing elements from across the periodic table. We present a conceptual review of a frequently used LMO analysis of NMR parameters calculated in the presence of spin-orbit interactions and other relativistic effects. An accompanying example focuses on the ¹⁵ N shielding in a heavy metal complex.

Why trans and not cis? – Molecular Dynamics and DFT study on selective separation of dihaloethene isomers using perethylated pillar[5]arene

The separation of mixtures of isomers is a daunting task. It is found that perethylated pillar[5]arene can separate trans-dichloroethene from its cis isomer. This work deals with the host-guest interactions...

Occurrence of Double Bond in π-Aromatic Rings: An Easy Way to Design Doubly Aromatic Carbon-Metal Structures

A chemical bonding of several metallabenzenes and metallabenzynes was studied via an adaptive natural density partitioning (AdNDP) algorithm and the induced magnetic field analysis. A unique chemical bonding pattern was discovered where the M=C (M: Os, Re) double bond coexists with the delocalized 6c-2e π-bonding elements responsible for aromatic properties of the investigated complexes. In opposition to the previous description where 8 delocalized π-electrons were reported in metallabenzenes and metallabenzynes, we showed that only six delocalized π-electrons are present in those molecules. Thus, there is no deviation from Hückel's aromaticity rule for metallabenzynes/metallabenzenes complexes. Based on the discovered bonding pattern, we propose two thermodynamically stable novel molecules that possess not only π-delocalization but also retain six σ-delocalized electrons, rendering them as doubly aromatic species. As a result, our investigation gives a new direction for the search for carbon-metal doubly aromatic molecules.

Inverse halogen dependence in anion 13C NMR

Halogens cause pronounced and systematic effects on the 13C NMR chemical shift (δ13C) of an adjacent carbon nucleus, usually leading to a decrease in the values across the halogen series. Although this normal halogen dependence (NHD) is known in organic and inorganic compounds containing the carbon atom in its neutral and cationic forms, information about carbanions is scarce. To understand how δ13C changes in molecules with different charges, the shielding mechanisms of CHX3, CX3+, and CX3- (X = Cl, Br, or I) systems are investigated via density functional theory calculations and further analyzed by decomposition into contributions of natural localized molecular orbitals. An inverse halogen dependence (IHD) is determined for the anion series as a result of the negative spin-orbit contribution instead of scalar paramagnetic effects. The presence of a carbon nonbonding orbital in anions allows magnetic couplings that generate a deshielding effect on the nucleus and contradicts the classical association between δ13C and atomic charge.

Computational 1 H NMR: Part 1. Theoretical background

This is the first one of the three closely interrelated reviews to be published in Magnetic Resonance in Chemistry dealing with accordingly theoretical background, chemical applications, and biochemical studies of and by means of computational ¹ H NMR. Presented in the first part of the review is a general outline of the modern theoretical methods and accuracy factors of computational ¹ H NMR involving locally dense basis set schemes, solvent effects, vibrational corrections, and relativistic effects performed at the density functional theory and/or nonempirical levels. This review is dedicated to Prof. Stephan Sauer in view of his invaluable contribution to the field of computational nuclear magnetic resonance.

Computational protocols for calculating 13C NMR chemical shifts

The most recent results dealing with the computation of ¹³C NMR chemical shifts in chemistry (small molecules, saturated, unsaturated and aromatic compounds, heterocycles, functional derivatives, coordination complexes, carbocations, and natural products) are reviewed, paying special attention to theoretical background and accuracy, the latter involving solvent effects, vibrational corrections, and relativistic effects.

"Through-Space" Relativistic Effects on NMR Chemical Shifts of Pyridinium Halide Ionic Liquids

We have investigated, using two-component relativistic density functional theory (DFT) at ZORA-SO-BP86 and ZORA-SO-PBE0 level, the occurrence of relativistic effects on the ¹ H, ¹³ C, and ¹⁵ N NMR chemical shifts of 1-methylpyridinium halides [MP][X] and 1-butyl-3-methylpyridinium trihalides [BMP][X₃ ] ionic liquids (ILs) (X=Cl, Br, I) as a result of a non-covalent interaction with the heavy anions. Our results indicate a sizeable deshielding effect in ion pairs when the anion is I^- and I₃ ^- . A smaller, though nonzero, effect is observed also with bromine while chlorine based anions do not produce an appreciable relativistic shift. The chemical shift of the carbon atoms of the aromatic ring shows an inverse halogen dependence that has been rationalized based on the little C-2s orbital contribution to the σ-type interaction between the cation and anion. This is the first detailed account and systematic theoretical investigation of a relativistic heavy atom effect on the NMR chemical shifts of light atoms in the absence of covalent bonds. Our work paves the way and suggests the direction for an experimental investigation of such elusive signatures of ion pairing in ILs.

Relativistic heavy atom effect on the 31 P NMR parameters of phosphine chalcogenides. Part 1. Chemical shifts

Four-component density functional theory calculations of ³¹ P NMR chemical shifts have been performed for the representative series of 56 phosphine chalcogenides in order to investigate an influence of different functional groups on the heavy atom relativistic effect on the NMR chemical shifts of light phosphorous atoms (Heavy Atom on Light Atom effect). The validity of the 4-component density functional theory approach used for the wide-scale calculations of the phosphorous chemical shifts in a wide series of phosphine chalcogenides has been confirmed on a small series of 5 representative compounds with the aid of high-quality coupled cluster singles and doubles calculations taking into account solvent, vibrational, and the relativistic corrections in comparison with the experiment.

Relativistic heavy atom effect on 13 C NMR chemical shifts initiated by adjacent multiple chalcogens

In this paper, we have investigated the cumulative peculiarity of the "heavy atom on light atom" effect on the ¹³ C NMR chemical shifts, initiated by the adjacent chalcogens. For this purpose, the most accurate hybrid computational scheme for the calculation of chemical shifts of carbon nuclei, directly bonded with several heavy chalcogens, is introduced and attested on the representative series of molecules. The best hybrid scheme combines the nonrelativistic coupled cluster-based approach with the different types of corrections, including vibrational, solvent, and relativistic. The dependences of the total relativistic corrections to carbon shielding constants in 2 series of model compounds, namely, X═¹³ C═Y (X, Y = O, S, Se, Te) and C(XH)_m (YH)_n (ZH)_p (QH)_s H_1-m H_1-n H_1-p H_1-s (X, Y, Z, Q = S, Se, Te and m, n, p, s = 0, 1), on the total atomic number of the adjacent chalcogens have been obtained.

Tosylation of alcohols: an effective strategy for the functional group transformation of organic derivatives of polyoxometalates

Recently, the organic functionalization of polyoxometalates (POMs) has drawn increasing interest, and an easy and effective route to achieve organic derivatives is of great importance. Herein, the first reported synthesis of a tosyl ester derivative of the polyoxometalate (Bu4N)2[V6O13{(OCH2)3CCH2SO3C7H4}2]·2.5CH3CN (compound 1) was performed by using DMAP as an activating reagent and triethylamine as an HCl scavenger. The tosyl ester was transformed into an azide or halide group by using sodium azide or sodium bromide, respectively, as the nucleophilic agent. Two derivatives of POMs, (Bu4N)2[V6O13{(OCH2)3CCH2N3}2]·4CH3CN (compound 2) and (Bu4N)2[V6O13{(OCH2)3CCH2Br}2] (compound 3), were easily obtained. All the compounds were structurally and compositionally characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, NMR spectroscopy, ESI-MS, UV-Vis spectroscopy and TGA. This work provides a new route for the functional group transformation of organic derivatives of polyoxometalates.

A Localized Molecular Orbital Study of the Halogen Substitution Effect on (103)Rh NMR Shielding in [Cp*RhX2]2, Where X = Cl, Br, or I

(103)Rh NMR parameters and the bonding structure of three complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have been studied with the help of natural bond orbitals (NBOs) and natural localized molecular orbitals (NLMOs). The complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have similar bonding structures, with the major difference being in the degree of covalency of the Rh-X bonds. The decomposition of (103)Rh NMR shielding into diamagnetic, paramagnetic, and spin-orbit terms shows that normal halogen dependence (NHD) of the (103)Rh NMR shift is defined mostly by the paramagnetic term, with the spin-orbit term being significantly smaller. The decomposition of (103)Rh shielding into spin-free NBO and NLMO contributions shows that (103)Rh shielding is dominated by Rh d-orbital deshielding contributions. We explain the NHD of the (103)Rh NMR shift with the increase in the energies of the virtual antibonding Rh-X orbitals along the X = Cl, Br, and I series.