Trans ligand effects on 195 Pt NMR shielding constants of square planar Pt(II) complexes
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Trans ligand effects on 195Pt NMR shielding constants of square planar Pt(II) complexes Athanassios C. Tsipis1 Received: 14 March 2020 / Accepted: 11 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The trans ligand effects on the isotropic σiso 195Pt NMR shielding constants, described by the unified term of trans-philicity, for a broad series of square planar trans-Pt(PMe3)2(X)L (X = H, CO, C H3, NH2, OH2, Cl) complexes, were investigated by DFT computational protocols at the 2-component spin–orbit zero-order approximation (2c-SO-ZORA) level of theory. The established trans-philicity sequences are almost identical for all series of complexes. The relative strength of trans-philicity is defined as the difference between the calculated σiso(SO) 195Pt NMR shielding constants for the complete set of ligands and the σiso(SO) 195Pt NMR shielding constant of the complex containing the ligand with the weakest trans-philicity. Noteworthily, the 195Pt NMR trans-philicity sequences retrieve the experimental trans-orienting series. The linear correlations between the σiso(SO) 195Pt NMR shielding constants and the σiso(SO) X NMR shielding constants shows that upon increase in the upfield shift of the σiso(SO) 195Pt NMR increase the downfield shift of the σiso(SO) X NMR shielding constants. The linear σiso(SO) 195Pt versus QPt correlations show that the increase in the negative natural atomic charge QPt increases the downfield shift of the σiso(SO) 195Pt shielding constants. Keywords 195Pt NMR · Trans-philicity · Square planar trans-Pt(PMe3)2(X)L complexes · Trans-philicity ladders · Transphilicity metrics
1 Introduction It has long been known that a coordinated ligand L in transition metal complexes can exert an intense effect on the strength of a M–X bond, where ligand X is trans with respect to L. The effect of L on the strength of M–X bond is a thermodynamic phenomenon known as the trans-influence while the effect of the ligand X on the lability of the trans ligand L is the trans-effect [1–9]. The trans-influence is also defined as the extent to which a ligand L weakens the trans M–X bond in the equilibrium state of the complex, whereas the trans-effect is considered to be the effect of a coordinated ligand L on the rate of substitution of the trans ligand. The Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00214-020-02663-3) contains supplementary material, which is available to authorized users. * Athanassios C. Tsipis [email protected] 1
Laboratory of Inorganic Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
trans-influence and trans-effects are interrelated and their separation is seldom achieved [8, 10, 11]. Though molecular descriptors such as trans bond length [12–14] and vibrational frequency of trans bond are often used to compare the trans-influence of different ligands, they do not give much insight into the extent of trans-influence as these descriptors are also affe
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