Quantum chemical calculations of 77 Se and 125 Te nuclear magnetic resonance spectral parameters and their structural applications

An accurate quantum chemical (QC) modeling of ⁷⁷ Se and ¹²⁵ Te nuclear magnetic resonance (NMR) spectra is deeply involved in the NMR structural assignment for selenium and tellurium compounds that are of utmost importance both in organic and inorganic chemistry nowadays due to their huge application potential in many fields, like biology, medicine, and metallurgy. The main interest of this review is focused on the progress in QC computations of ⁷⁷ Se and ¹²⁵ Te NMR chemical shifts and indirect spin-spin coupling constants involving these nuclei. Different computational methodologies that have been used to simulate the NMR spectra of selenium and tellurium compounds since the middle of the 1990s are discussed with a strong emphasis on their accuracy. A special accent is placed on the calculations resorting to the relativistic methodologies, because taking into account the relativistic effects appreciably influences the precision of NMR calculations of selenium and, especially, tellurium compounds. Stereochemical applications of quantum chemical calculations of ⁷⁷ Se and ¹²⁵ Te NMR parameters are discussed so as to exemplify the importance of integrated approach of experimental and computational NMR techniques.

Understanding 125Te NMR chemical shifts in disymmetric organo-telluride compounds from natural chemical shift analysis

Magnetic coupling of the lone pair: theoretical investigations reveal the origin of ¹²⁵Te chemical shift in disymmetric organotellurides

Spin-orbit effects on the 125Te magnetic-shielding tensor: A cluster-based ZORA/DFT investigation

Cluster-based calculations of ¹²⁵Te magnetic-shielding tensors demonstrate that inclusion of spin-orbit effects is necessary to obtain the best agreement of theoretical predictions with experiment. The spin-orbit contribution to shielding depends on the oxidation state and stereochemistry of the ¹²⁵Te site. Comparison of the performance of various density functionals indicates that GGA functionals behave similarly to each other in predicting NMR magnetic shielding. The use of hybrid functionals improves the predictive ability on average for a large set of ¹²⁵Te-containing materials. The amount of Hartree-Fock exchange affects the predicted parameters. Inclusion of larger Hartree-Fock exchange contributions in hybrid functionals results in larger slopes of the correlation between calculated magnetic-shielding and experimental chemical-shift principal components, by 10-15% from the ideal value.

Relativistic Effect on 1 J(M,C) in Me4 M, Me3 M- , Ph4 M, and Ph3 M- (M=Pb, Sn, Ge, Si, and/or C): Role of s-Type Lone Pair Orbitals in the Distinct Effect for the Anionic Species

Indirect one-bond nuclear spin-spin couplings between M and C [¹ J(M,C)] in Me₄ M, Me₃ M^- , Ph₄ M, and Ph₃ M^- (M=Pb, Sn, Ge, Si, C) are analyzed with consideration of the relativistic effect and by employing Slater-type basis sets. The evaluated total values ¹ J_TL (M,C) reproduced the observed values with some systematic calculation errors. Fermi contact terms ¹ J_FC (M,C) contribute predominantly to ¹ J_TL (M,C) (≈99 %). A distinct relativistic effect on ¹ J(Pb,C) is predicted for Me₃ Pb^- and Ph₃ Pb^- . The mechanisms for the distinct effect are elucidated by using the comparison between Me₃ Pb^- and Me₄ Pb as an example. The contributions to ¹ J_FC (M,C) [or ¹ J_SD+FC (M,C), where SD denotes the spin-dipolar term] are decomposed into those of occupied orbitals and occupied-to-unoccupied transitions. The s-type lone-pair orbitals are demonstrated to contribute to the distinct relativistic effect on ¹ J(Pb,C) of Me₃ Pb^- (and Ph₃ Pb^- ). The results are in sharp contrast to the cases of ¹ J(M,C) for M atoms lighter than Pb, such as Si, and are explained by the s character of the M-C bonds. This treatment enables visualization and clear recognition the origin of the nuclear couplings for the species exhibiting a relativistic effect.

On the calculation of second-order magnetic properties using subsystem approaches in a relativistic framework

The implementation of second-order magnetic properties in a frozen density embedding scheme in a four component relativistic framework is outlined and applied to model H₂X–H₂O systems (X = Se, Te, Po).