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

摘要

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]~(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 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]~(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 [PtF _(6-n)Cl_n]~(2-) and [PtF_(6-n)Br _n]~(2-) may be expected. The discrepancies generally increase in the order [PtCl_(6-n)Br_n]~(2-) < [PtBr _(6-n)I_n]~(2-) < [PtCl_(6-n)I _n]~(2-) < [PtF_(6-n)Br_n] ~(2-)≈ [PtF_(6-n)Cl_n]~(2-), 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/? for [PtF_6]~(2-), [PtCl_6]~(2-), [PtBr_6]~(2-) and [PtI _6]~(2-), respectively.