A DFT and 59Co Solid-State NMR Study of the Chemical Shielding Property and Electronic Interaction in the Metalloporphyrin System

Automatic fitting of multiple-field solid-state NMR spectra

The NMR lineshapes produced by half-integer quadrupolar nuclei are sensitive to 11 distinct fit parameters per inequivalent site. To date, automatic fitting routines have failed to replace manual parameter insertion and evaluation due to the importance of local minima and the need for fitting multiple-field magic-angle spinning (MAS) and static spectra simultaneously. Herein we introduce a new tool, AMES-Fit (Automatic Multiple Experiment Simulation and Fitting), to automatically find the global best-fit simulation parameters for a series of multiple-field NMR lineshapes. AMES-Fit uses an adaptive step size random search algorithm to dynamically probe parameter space and requires minimal human input. The best fits are obtained in a few minutes of computation time that would otherwise have required several person-hours of work. The program is freely available and open-source.

The Scope of the Applicability of Non-relativistic DFT Calculations of NMR Chemical Shifts in Pyridine-Metal Complexes for Applied Applications

Heavy metals are toxic, but it is impossible to stop using them. Considering the variety of molecular systems in which they can be present, the multicomponent nature and disorder of the structure of such systems, one of the most effective methods for studying them is NMR spectroscopy. This determines the need to calculate NMR chemical shifts for expected model systems. For elements beyond the third row of the periodic table, corrections for relativistic effects are necessary when calculating NMR parameters. Such corrections may be necessary even for light atoms due to the shielding effect of a neighboring heavy atom. This work examines the extent to which non-relativistic DFT calculations are able to reproduce experimental 15N and 113Cd NMR chemical shift tensors in pyridine-metal coordination complexes. It is shown that while for the calculation of 15N NMR chemical shift tensors there is no real need to consider relativistic corrections, for 113Cd, on the contrary, none of the tested calculation methods could reproduce the experimentally obtained tensor to any extent correctly.

NMR chemical shifts of urea loaded copper benzoate. A joint solid-state NMR and DFT study

We report solid-state ¹³C NMR spectra of urea-loaded copper benzoate, Cu₂(C₆H₅CO₂)₄·2(urea), a simplified model for copper paddlewheel-based metal-organic frameworks (MOFs), along with first-principles density functional theory (DFT) computation of the paramagnetic NMR (pNMR) chemical shifts. Assuming a Boltzmann distribution between a diamagnetic open-shell singlet ground state (in a broken-symmetry Kohn-Sham DFT description) and an excited triplet state, the observed δ(¹³C) values are reproduced reasonably well at the PBE0-⅓/IGLO-II//PBE0-D3/AE1 level. Using the proposed assignments of the signals, the mean absolute deviation between computed and observed ¹³C chemical shifts is below 30 ppm over a range of more than 1100 ppm.

Structural Insights from 59 Co Solid-State NMR Experiments on Organocobalt(I) Catalysts

A series of fumarate-based organocobalt(I) [CoCp(CO)(fumarate)] catalysts is synthesized and characterized by X-ray crystallography, multinuclear (¹³ C and ⁵⁹ Co) solid-state NMR spectroscopy, and ⁵⁹ Co NQR spectroscopy. Given the dearth of ⁵⁹ Co solid-state NMR studies on Co^I compounds, the present work constitutes the first systematic characterization of the ⁵⁹ Co electric field gradient and chemical shift tensors for a series of cobalt complexes in this oxidation state. Using X-ray crystallography, the molecular geometry about the Co^I centre is found to be nearly identical in all compounds studied herein. Owing to the ⁵⁹ Co nucleus' large chemical shift range, solid-state NMR experiments are found to be able to detect small structural differences between the individual organocobalt(I) compounds. With the aid of density functional theory calculations on these complexes, it is shown that the ⁵⁹ Co chemical shift anisotropy and the ⁵⁹ Co quadrupolar coupling constant are both extremely sensitive gauges of the Fu-Co-Cp bond angle, providing a link between these ⁵⁹ Co NMR observables and the catalysts' structures.

Toward a physical interpretation of substituent effects: the case of fluorine and trifluoromethyl groups

The application of ab initio and DFT computational methods at six different levels of theory (MP2/cc-pVDZ, MP2/aug-cc-pVTZ, B3LYP/cc-pVDZ, B3LYP/aug-cc-pVTZ, M06/cc-pVDZ, and M06/aug-cc-pVTZ) to meta- and para-substituted fluoro- and trifluoromethylbenzene derivatives and to 1-fluoro- and 1-trifluoromethyl-2-substituted trans-ethenes allowed the study of changes in the electronic and geometric properties of F- and CF3-substituted systems under the impact of other substituents (BeH, BF2, BH2, Br, CFO, CHO, Cl, CN, F, Li, NH2, NMe2, NO, NO2, OH, H, CF3, and CH3). Various parameters of these systems have been investigated, including homodesmotic reactions in terms of the substituent effect stabilization energy (SESE), the π and σ electron donor-acceptor indexes (pEDA and sEDA, respectively), the charge on the substituent active region (cSAR, known earlier as qSAR), and bond lengths, which have been regressed against Hammett constants, resulting mostly in an accurate correspondence except in the case of p-fluorobenzene derivatives. Moreover, changes in the characteristics of the ability of the substituent to attract or donate electrons under the impact of the kind of moiety to which the substituent is attached have been considered as the indirect substituent effect and investigated by means of the cSAR model. Regressions of cSAR(X) versus cSAR(Y) for any systems X and Y allow final results to be obtained on the same scale of magnitude.

X-ray diffraction, Raman spectroscopic, and solid-state NMR studies of the group 14 metal-(tetracarbonyl)cobalt complexes Ph3MCo(CO)4 (M = Si, Sn, Pb)

Single-crystal X-ray diffraction studies illustrate that the three title compounds are isomorphous, belonging to the triclinic space group P[Formula: see text], with slightly distorted trigonal bipyramidal geometry about cobalt. The solid-state 29Si, 119Sn, and 207Pb cross-polarization magic angle spinning (CP MAS) NMR spectra are presented. The indirect spin–spin coupling constant (J), quadrupolar–dipolar shift (d), direct dipolar coupling constant (D' ), anisotropy in spin–spin coupling (ΔJ), and the chemical shift tensor were extracted. A plot of the reduced coupling constant vs. s-electron densities at the nucleus indicates that the Fermi contact term may be dominant for the tin and lead complexes; however, the large ΔJ for all complexes indicate that there are also significant anisotropic terms. Trends in the Raman scattering spectra are also discussed.Key words: 29Si, 119Sn, and 207Pb CP MAS NMR, tetracarbonyl cobalt, spin–spin coupling, chemical shift tensor, quadrupole coupling, Fermi contact, cobalt–group 14.