Calculations of the indirect nuclear spin-spin coupling constants of PbH 4

Abstract

We report ab initio calculations of the indirect nuclear spin±spin coupling constants of PbH 4 using a basis set which was specially optimized for correlated calculations of spin±spin coupling constants. All nonrelativistic contributions and the most important part of the spin±orbit correction were evaluated at the level of the random phase approximation. Electron correlation corrections to the coupling constants were calculated with the multicon®gurational linear-response method using extended complete and restricted active space wavefunctions as well as with the second-order polarization propagator approximation and the second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes. The eects of nuclear motion were investigated by calculating the coupling constants as a function of the totally symmetric stretching coordinate. We ®nd that the Fermi contact term dominates the Pb·H coupling, whereas for the H·H coupling it is not more important than the orbital paramagnetic and diamagnetic contributions. Correlation aects mainly the Fermi contact term. Its contribution to the one-bond coupling constant is reduced by correlation, independent of the method used; however, the dierent correlated methods give ambiguous results for the Fermi contact contribution to the H·H couplings. The dependence of both coupling constants on the Pb·H bond length is dominated by the change in the Fermi contact term. The geometry dependence is, however, overestimated in the random phase approximation.

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 2. Strained polycarbocycles

“…Uncorrelated HF-SCF calculations overestimate the values of J(C,C) on average by a factor of ca 1.5-2, whereas taking into account electronic correlation at the SOPPA level results in reliable values of J(C,C) in very good agreement with experiment. Electronic correlation effects dramatically decrease the values of all carbon-carbon couplings in the compounds under study to bring them into agreement with the experimental values, and this effect totals to ca [15][16][17][18][19][20] Hz for the 'relatively normal' J(C,C) and to more than 100 Hz (!) for the 'strikingly unusual' couplings.…”

Solvent Effects on Heavy Atom Nuclear Spin−Spin Coupling Constants: A Theoretical Study of Hg−C and Pt−P Couplings

“…The DSO/PSO and FC/SD coupling mechanisms originate from the interaction of the nuclear spins with the electronic orbital and spin magnetic moments, respectively. If the electrons are treated relativistically, coupling of electronic spin and orbital angular momentum results in cross terms between the DSO/PSO and FC/SD nuclear spin−spin coupling mechanisms, of which the FC−PSO cross term was found to be the most important one in a number of systems. , For sixth row element compounds, spin−orbit coupling can often be neglected to lowest order, resulting in a so-called scalar relativistic treatment. This approach has, for example, been used 12 to obtain the data presented in Figure .…”

Nonempirical calculations of NMR indirect spin-spin coupling constants

“…7,9,10,14 Results of the SOPPA calculations of the title 1 J(C,C) and 1 J(C,H) in the model series 8-13 in comparison with the experimental values in the original compounds 1-7 are compiled in Table 2. First of all, it should be noted that both one-bond couplings involving the˛-imino carbon, 1 J(C,C) and 1 J(C,H), show marked dependence on the orientation of the nitrogen lone pair in good agreement with the available experimental data which enables one to perform the unambiguous assignment of all of the parent azomethines 1-7 to the E-configuration.…”

“…Calculations of 1 J(C,C) and 1 J(C,H) in the model series 8-13 were performed at the second-order polarization propagator approach (SOPPA) 8 level approved for the calculation of spin-spin coupling constants of different types in a number of publications by Sauer et al 9,10 Correlationconsistent basis set cc-pVDZ of Dunning et al 11 augmented with the core s-functions of Woon and Dunning 12 on coupled carbons, cc-pVDZ-Cs, and basis set of Sauer et al, 10f augcc-pVTZ-J, with the tight s-functions of Schulman and Kaufman 13 on coupled hydrogens were applied, as described elsewhere.…”