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Shielding and Indirect Spin–Spin Coupling Tensors in the Presence of a Heavy Atom: An Experimental and Theoretical Study of Bis(phenylethynyl)mercury

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posted on 2012-11-01, 00:00 authored by Adam Gryff-Keller, Anna Kraska-Dziadecka, Sergey Molchanov, Artur Wodyński
Magnetic shielding and indirect spin–spin coupling phenomena are tensorial properties and both their isotropic and anisotropic parts do affect NMR spectra. The involved interaction tensors, σ̂ and , can nowadays be theoretically calculated, although the reliability of such methods in the case of anisotropic parameters, Δσ and ΔJ, in systems involving heavy nuclei, yet demands testing. In this communication the results of the experimental and theoretical investigations of bis­(phenylethynyl)mercury (I) labeled with 13C isotope at positions neighboring Hg are reported. The theoretical calculations of molecular geometry and values of NMR parameters for I have been performed by the ZORA/DFT method, including the relativistic scalar and spin–orbit coupling contributions, using the PBE0 functional and TZP (or jcpl) basis set. These values have been confronted with the experimentally measured ones. The isotropic parameters have been measured by the standard 13C and 199Hg NMR spectra. The shielding anisotropies for the atoms in the central part of molecule I have been determined in a liquid sample using magnetic relaxation measurements. The relaxation data have been interpreted within the rotational diffusion theory, assuming the symmetrical top reorientation model. The anisotropies of one-bond 13C–199Hg and two-bond 13C–Hg–13C spin–spin couplings have been determined exploiting the temperature-dependent 13C NMR spectra of I in the ZLI1167 liquid-crystal phase. We have found that our theoretical calculations reproduce experimental values of both isotropic and anisotropic NMR parameters very well.

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