195Pt Chemical shifts and 1JPt-Pt coupling constants were measured for a series of head-to-head (HH) and head-to-tail (HT) amidato-bridged cis-diammineplatinum(III) dinuclear complexes involved in the axial water substitution reactions with halide ions (X- = Cl -, Br-): HH-[Pt2(NH3) 4(μ-amidato)2L1L2]n+ ≡ [L1-Pt(N2O2)-Pt(N4)-L 2]n+ (amidato = α-pyridonato, α-pyrrolidonato, and pivalamidato) and HT-[Pt2(NH3)4(μ- α-pyridonato)2L1L2]n+ ≡ [L1-Pt(N3O)-Pt(N3O)-L2] n+; the diaqua (L1, L2 = H2O, n = 4), the aquahalo (L1 = X-, L2 = H2O, n = 3), and the dihalo complexes (L1, L2 = X-, n = 2). The 195Pt NMR spectroscopic data were considered in relation to the lability in the axial ligand substitution reaction and the electron distribution along the Pt-Pt bond. The NMR spectroscopic data suggested different electron distributions along the Pt-Pt bonds in all the HH dimers and in the HT aquahalo dimers, such as [L1-PtIV(N 2O2)-PtII(N4)-L2] n+ and [X-PtIV(N3O)-PtII-(N 3O)-OH2]3+, respectively. Relative shifts of the 195Pt NMR signals for each substitution step indicate that the replacement of the axial water ligand by X- affects more effectively the electron density of the opposite Pt atom than that of the substituted one.
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