Molecular Dynamics Computational Study of the199Hg−199Hg NMR Spin−Spin Coupling Constants of [Hg−Hg−Hg]2+in SO2Solution

Spin-Spin Coupling Constant Based on Reference Interaction Site Model Self-Consistent Field with Constrained Spatial Electron Density

A method for computing spin-spin coupling constants (SSCCs) using the reference interaction site model self-consistent field with constrained spatial electron density (RISM-SCF-cSED) is proposed for the first time. Describing solvents using integral equation theory allows us to reflect solvent effects at atomic resolution in SSCCs while accounting for thermal fluctuations at a low computational cost. Applying the method to water, 1,1-difluoroethylene, and 1-methylaminomethylene-2-naphthalenone revealed that the solvent shift was evaluated to a greater extent than in the continuum solvent model. The origin of this phenomenon was analyzed in terms of the physical mechanisms underlying SSCCs.

Relativistic and QED corrections to one-bond indirect nuclear spin-spin couplings in X$_2^{2+}$ and X$_3^{2+}$ ions (X = Zn, Cd, Hg)

The indirect spin-spin coupling tensor, $\bm J$, between mercury nuclei in systems containing this element can be of the order of few kHz and one of the largest measured. We analysed the physics behind the electronic mechanisms that contribute to the one- and two-bond couplings $^n \bm{J}_{\mathrm{Hg}-\mathrm{Hg}}$ ($n=1, 2$). For doing so, we performed calculations for $J$-couplings in the ionized $X_2^{2+}$ and $X_3^{2+}$ linear molecules ($X$ = Zn, Cd, Hg) within polarization propagator theory, using the random phase approximation and the pure zeroth--order approximation with Dirac--Hartree--Fock and Dirac--Kohn--Sham orbitals, both at four-component and ZORA levels. We show that the ``paramagnetic-like' mechanism contribute with more than 99.98\% to the total isotropic value of the coupling tensor. By analyzing the molecular and atomic orbitals involved in the total value of the response function, we find that the $s$-type valence atomic orbitals have a predominant role in the description of the coupling. This fact allows us to develop an effective model from which QED effects on $J$-couplings in the aforementioned ions can be estimated. Those effects were found to be within the interval $(0.7;~1.7)$\% of the total relativistic effect on isotropic one-bond $^1\bm{J}$ coupling, though ranging those corrections between the interval $(-0.4;~-0.2)$\% in Zn-containing ions, to $(-1.2;~-0.8)$\% in Hg-containing ions, of the total isotropic coupling constant in the studied systems. The estimated QED corrections show a visible dependence on the nuclear charge $Z$ of each atom $X$ in the form of a power-law proportional to $Z_X^5$.

Microsolvation of methylmercury: structures, energies, bonding and NMR constants (199Hg,13C and17O)

Hartree–Fock (HF) and second order perturbation theory (MP2) calculations within the scalar and full relativistic frames were carried out in order to determine the equilibrium geometries and interaction energies between cationic methylmercury (CH₃Hg⁺) and up to three water molecules.

Bis-tetradentate complexes of Cd(II) and Hg(II) with N8 coordination: structural and NMR comparisons

Tripodal N4 ligands tris[(1-methylimidazol-2-yl)methyl]amine (L1), bis[(1-methylimidazol-2-yl)methyl][(2-pyridyl)methyl]amine (L2) and [(1-methylimidazol-2-yl)methyl]-bis-[(2-pyridyl)methyl]amine (L3) were used to prepare five new [ML2](ClO4)2 (M = Cd(II), Hg(II)) complexes. All complexes had N8 metal coordination and a trans-bicapped octahedral structure as determined by X-ray crystallography. Metal-nitrogen bond distances generally decreased in the order M-Namine > M-Npyridyl > M-Nimidazoyl, and the perchlorates were well separated from the metal ions. Variable temperature solution state (1)H NMR spectroscopy revealed conditions for slow intramolecular reorganization were more readily accessible for the Cd(II) complexes than for the Hg(II) complexes. Both protons of imidazoyl ring ligand components had large, comparable J((199)Hg(1)H) despite sizable differences in nuclear separation.

Quadrupolar NMR Spin Relaxation Calculated Using Ab Initio Molecular Dynamics: Group 1 and Group 17 Ions in Aqueous Solution

Electric field gradient (EFG) fluctuations for the monoatomic ions (7)Li(+), (23)Na(+), (35)Cl(-), (81)Br(-), and (127)I(-) in aqueous solution are studied using Car-Parrinello ab initio molecular dynamics (aiMD) simulations based on density functional theory. EFG calculations are typically performed with 1024 ion-solvent configurations from the aiMD simulation, using the Zeroth Order Regular Approximation (ZORA) relativistic Hamiltonian. Autocorrelation functions for the spherical EFG tensor elements are computed, transformed into the corresponding spectral densities (under the extreme narrowing condition), and subsequently converted into NMR quadrupolar relaxation rates for the ions. The relaxation rates are compared with experimental data. The order of magnitude is correctly predicted by the simulations. The computational protocol is tested in detail for (81)Br(-).

Modeling of heavy-atom-ligand NMR spin-spin coupling in solution: molecular dynamics study and natural bond orbital analysis of Hg-C coupling constants

Ab initio molecular dynamics (MD) and relativistic density functional NMR methods were applied to calculate the one-bond Hg-C NMR indirect nuclear spin-spin coupling constants (J) of [Hg(CN)(2) ] and [CH(3) HgCl] in solution. The MD averages were obtained as J((199) Hg-(13) C)=3200 and 1575 Hz, respectively. The experimental Hg-C spin-spin coupling constants of [Hg(CN)(2) ] in methanol and [CH(3) HgCl] in DMSO are 3143 and 1674 Hz, respectively. To deal with solvent effects in the calculations, finite "droplet" models of the two systems were set up. Solvent effects in both systems lead to a strong increase of the Hg-C coupling constant. From a relativistic natural localized molecular orbital (NLMO) analysis, it was found that the degree of delocalization of the Hg 5d(σ) nonbonding orbital and of the HgC bonding orbital between the two coupled atoms, the nature of the trans Hg-C/Cl bonding orbital, and the s character of these orbitals, exhibit trends upon solvation of the complexes that, when combined, lead to the strong increase of J(Hg-C).