A comparison of experimental and DFT calculations of ¹⁹⁵Pt NMR shielding trends for [PtX(n)Y(6-n)](2-) (X, Y = Cl, Br, F and I) anions.

A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT (195)Pt chemical shifts of a series of octahedral PtX(6-n)Y(n) complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant σ(dia), σ(para) and σ(SO) shielding contributions. The discrepancies between the experimental and the DFT-calculated (195)Pt chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the PtCl(6-n)Br(n) series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of PtF(6-n)Cl(n) and PtF(6-n)Br(n) may be expected. The discrepancies generally increase in the order PtCl(6-n)Br(n) < PtBr(6-n)I(n) < PtCl(6-n)I(n) < PtF(6-n)Br(n) ≈ PtF(6-n)Cl(n), and show a striking correlation with the increase in electronegativity difference Δχ between the two halide ligands (X(-) and Y(-)) bound to Pt(IV) for these anions: 0.09 < 0.52 < 0.63 < 1.36 ≈ 1.27, respectively. The computed (195)Pt sensitivity to Pt-X bond displacement, ∂(δ(195)Pt)/∂(ΔPt-X), of these complexes is very large and depends on the halide ion, decreasing from 24 800, 18 300, 15 700 to 12 000 ppm/Å for PtF(6), PtCl(6), PtBr(6) and PtI(6), respectively.