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 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 [PtX nY4- 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 5d z² 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 [PtX nY4- 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). [ABSTRACT FROM AUTHOR]