Study of the aqueous reactions of K[Pt(DMSO)Cl3] with nitrile ligands and crystal structures of Cl(DMSO)Pt(μ-C4H8NO)2Pt(DMSO)Cl and Cl(DMSO)Pt(μ-C5H10NO)2Pt(DMSO)Cl
The aqueous reactions of K[Pt(DMSO)Cl3] with nitriles were studied in different conditions of pH. At normal pH (≈2.4), the ligands RCN, where R is an alkyl group, produced the yellow complexes Pt(DMSO)(R-CN)Cl2. Infrared spectroscopy suggested cis isomers. The 195Pt NMR spectra of the compounds show a resonance around −3000 ppm. The same reactions in neutral medium (pH adjusted to ~7 with NaOH) produced acetamido-bridged dimers (DMSO)ClPt(μ-RCONH)2Pt(DMSO)Cl with all the ligands studied: propionitrile, butyronitrile, dimethylacetonitrile, trimethylacetonitrile, fluoroacetonitrile, chloroacetonitrile, bromoacetonitrile, and dibromoacetonitrile. The results of 195Pt NMR spectroscopy show a head-to-tail isomer, since only one signal around −2750 ppm is observed for each complex. These dimeric compounds are all blue or green depending on the ligand. The same dimers are obtained with all the haloacetonitrile ligands when the pH is not adjusted (≈2.4). The crystal structures of Cl(DMSO)Pt(μ-C4H8NO)2Pt(DMSO)Cl (1) and Cl(DMSO)Pt(μ-C5H10NO)2Pt(DMSO)Cl (2) were determined. The results confirm that the dimers are head-to-tail isomers with the DMSO ligands located in trans position to the O-acetamido atoms. The two crystals belong to the Pna21 space group with a = 11.112(4), b = 20.414(9), c = 10.161(4) Å for 1 and a = 11.607(6), b = 20.113(11), and c = 10.641(5) Å for 2. The structures were refined to R = 0.054 for 1 and R = 0.056 for 2. The Pt—Cl bond lengths are 2.328(10), 2.293(10) Å for 1 and 2.317(9), 2.317(10) Å for 2, while the Pt—S bond lengths are 2.173(10), 2.193(10) for 1 and 2.180(9), 2.176(9) Å for 2. The Pt—O bonds vary from 1.91(2) to 2.08(2) and the Pt—N from 1.88(2) to 2.03(2) Å. The dihedral angle between the two Pt(II) planes is 36°.