Title

Synthesis and Characterization of Pt(II) Complexes with Pyridyl Ligands: Elongated Octahedral Ion Pairs and Other Factors Influencing 1H NMR Spectra

Document Type

Article

Publication Date

8-21-2017

Abstract

© 2017 American Chemical Society. Our goal is to develop convenient methods for obtaining trans-[PtII(4-Xpy)2Cl2] complexes applicable to 4-substituted pyridines (4-Xpy) with limited volatility and water solubility, properties typical of 4-Xpy, with X being a moiety targeting drug delivery. Treatment of cis-[PtII(DMSO)2Cl2] (DMSO = dimethyl sulfoxide) with 4-Xpy in acetonitrile allowed isolation of a new series of simple trans-[PtII(4-Xpy)2Cl2] complexes. A side product with very downfield H2/6 signals led to our synthesis of a series of new [PtII(4-Xpy)4]Cl2 salts. For both series in CDCl3, the size of the H2/6 δ[coordinated minus "free" 4-Xpy H2/6 shift] decreased as 4-Xpy donor ability increased from 4-CNpy to 4-Me2Npy. This finding can be attributed to the greater synergistic reduction in the inductive effect of the Pt(II) center with increased 4-Xpy donor ability. The high solubility of [PtII(4-Xpy)4]Cl2 salts in CDCl3 (a solvent with low polarity) and the very downfield shift of the [PtII(4-Xpy)4]Cl2 H2/6 signals for the solutions provide evidence for the presence of strong {[PtII(4-Xpy)4]2+,2Cl-} ion pairs that are stabilized by multiple CH···Cl contacts. This conclusion gains considerable support from [PtII(4-Xpy)4]Cl2 crystal structures revealing that a chloride anion occupies a pseudoaxial position with nonbonding (py)C-H···Cl contacts (2.4-3.0 Å). Evidence for (py)C-H···Y contacts was obtained in NMR studies of [PtII(4-Xpy)4]Y2 salts with Y counterions less capable of forming H-bonds than chloride ion. Our synthetic approaches and spectroscopic analysis are clearly applicable to other nonvolatile ligands.

Publication Source (Journal or Book title)

Inorganic Chemistry

First Page

9781

Last Page

9793

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