A Theoretical Study of the NMR Spin-Spin Coupling Constants of the Complexes [(NC)₅Pt-Tl(CN)_n]^n- (n = 0-3) and [(NC)₅Pt-Tl-Pt(CN)₅]^3-: A Lesson on Environmental Effects

The molecular geometries and the nuclear spin-spin coupling constants of the complexes [(NC)₅Pt-Tl(CN)_n]^n-, n = 0-3, and the related system [(NC)₅Pt-Tl-Pt(CN)₅]^3- are studied. These complexes have received considerable interest since the first characterization of the n = 1 system by Glaser and co-workers in 1995 [J. Am. Chem. Soc. 1995, 117, 7550-7551]. For instance, these systems exhibit outstanding NMR properties, such as extremely large Pt-Tl spin-spin coupling constants. For the present work, all nuclear spin-spin coupling constants J _Pt-Tl, J_Pt-C, and J_Tl-C have been computed by means of a two-component relativistic density functional approach. It is demonstrated by the application of increasingly accurate computational models that both the huge J_Pt-Tl for the complex (NC)₅Pt-Tl and the whole experimental trend among the series are entirely due to solvent effects. An approximate inclusion of the bulk solvent effects by means of a continuum model, in addition to the direct coordination, proves to be crucial. Similarly drastic effects are reported for the coupling constants between the heavy atoms and the carbon nuclei. A computational model employing the statistical average of orbital-dependent model potentials (SAOP) in addition to the solvent effects allows to accurately reproduce the experimental coupling constants within reasonable limits.