A comparison of experimental and DFT calculations of 195Pt NMR shielding trends for [PtXnY6-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 Pt-195 chemical shifts of a series of octahedral [PtX6-nYn](2-) 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 sigma(dia), sigma(para) and sigma(SO) shielding contributions. The discrepancies between the experimental and the OFT-calculated Pt-195 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 [PtCl6-nBrn](2-) 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 [PtF6-nCln](2-) and [PtF6-nBrn](2-) may be expected. The discrepancies generally increase in the order [PtCl6-nBrn](2-) <[PtBr6-nIn](2-) < [PtCl6-nIn](2-) < [PtF6-nBrn](2-) approximate to [PtF6-nCln](2-), and show a striking correlation with the increase in electronegativity difference Delta(chi) between the two halide ligands (X(-)and Y-) bound to Pt(IV) for these anions: 0.09 < 0.52 < 0.63 < 1.36 approximate to 1.27, respectively. The computed Pt-195 sensitivity to Pt-X bond displacement, partial derivative(delta Pt-195)/partial derivative(Delta Pt-X), of these complexes is very large and depends on the halide ion, decreasing from 24800, 18 300, 15 700 to 12 000 ppm/angstrom for [PtF6](2-), [PtCl6](2-), [PtBr6](2-) and [Ptl(6)](2-), respectively. Copyright (C) 2010 John Wiley & Sons, Ltd.