N-15 SOLID-STATE NMR-STUDY OF LIGANDS IN PLATINUM MIXED-VALENCE COMPLEXES

N-15 solid-state NMR spectra have been recorded on a series of platinum complexes with two different amine ligands, N-15-enriched 1,2-diaminoethane (en) and natural abundance 3,7-diazanonane-1,9-diamine (2,3,2-tet). The results show that the N-15 chemical shift and J coupling to Pt-195 are very sensitive to the effective oxidation state of the metal atom and that, in both discrete platinum(II) and platinum(IV) complexes as well as in mixed-valence complexes which can be formed therefrom, the platinum atom environments become more similar on changing from a chloro to a bromo to an iodo species. This trend is attributable to the fall in the electronegativity of the halogen atom (Cl > Br > 1) and thus to a lowering of the effective positive charge on the metal atom as the halogen atom is changed in this order, and not to increased valence delocalization upon formation of a linear chain.