Square-Planar PtII versus Octahedral PtIV Halido Complexes: 195Pt NMR Explained by a Simple Empirical Approach

In this work, we show by a simple empirical approach that a linear relationship between observed Pt-195 NMR frequencies and the overall sum of the ionic radii of the coordinated halido ligands [sigma(r(h))] exists in square-planar Pt-II complexes of the type [PtXnY4-n](2-) (1n4; X,Y = Cl, Br, I). Another finding was that such square-planar complexes could be empirically described as octahedral complexes, with the two lobes of the 5d(z)(2) orbital above and below the coordination plane acting as two pseudo-halido ligands, each showing a constant apparent radius of around 207 pm. According to our approach, the overall apparent radius of around 415 pm produces constant Pt-195 NMR shielding for all [PtXnY4-n](2-) complexes of about 10450 ppm. This result is 1) consistent with the theoretically calculated overall 5d shell lone-pair shielding observed in square-planar Pt-II with respect to octahedral Pt-IV complexes and 2) almost coincident with the already measured chemical shift anisotropy (CSA) of the K-2[PtCl4] complex both in solution and in the solid state (single crystal).