High-resolution solid-state N-15 NMR spectroscopy is used to demonstrate unambiguously the presence of Cl- Pt-IV-Br units in [Pt(en)(2)][Pt(en)(2)Cl2-2xBr2x](ClO4)(4) complexes (0 less than or equal to x less than or equal to 1). The spectra provide information on the distribution of the halogen atoms around the Pt(IV) sites and allow a measure of the bromine concentration in the chain to be made. It is demonstrated that the halogen distribution is fairly close, but not identical, to random about this site. This suggests that the overall distribution of halogen atoms throughout the mixed-valence chain can be treated as being virtually random.