¹⁹⁵Pt NMR spectra of head-to-head and head-to-tail amidato-bridged platinum(III) dinuclear complexes

¹⁹⁵Pt Chemical shifts and ¹J_Pt-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-Pt^IV(N ₂O₂)-Pt^II(N₄)-L²] ⁿ⁺ and [X-Pt^IV(N₃O)-Pt^II-(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.