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

Abstract

In this work, we show by a simple empirical approach that a linear relationship between observed 195Pt NMR frequencies and the overall sum of the ionic radii of the coordinated halido ligands [Σ(rh)] exists in square‐planar PtII complexes of the type [PtXnY4–n]2– (1 ≤ n ≤ 4; 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 5dz² 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 195Pt 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 PtII with respect to octahedral PtIV complexes and 2) almost coincident with the already measured chemical shift anisotropy (CSA) of the K2[PtCl4] complex both in solution and in the solid state (single crystal).