Solid-state 13C high-resolution NMR in one-dimensional halogen-bridged nickel complexes and palladium(II)—palladium(IV) mixed-valence complexes

Abstract

Solid-state high-resolution 13C NMR (CP/MAS) spectra were measured on one-dimensional halogen-bridged complexes [Ni(R,R-chxn) 2X]X 2 (X = Cl, Br; R,R-chxn = 1R,2R-cyclohexanediamine) to elucidate the metal valence state. The spectra observed were compared with those of Pd(II)–Pd(IV) mixed-valence complexes: [Pd(R,R-chxn) 2] [PdX 2(R,R-chxn) 2]Y 4 (X = Cl, Br; Y = ClO 4, Cl) and [Pd(en) 2] [PdX 2(en) 2] (ClO 4) 4 (X = Cl, Br; en = ethylenediamine) together with a monomer 'Pd(II) complex [Pd(R,R-chxn) 2]Cl 2. The one-dimensional Pd complexes showed a clear 1:1 doublet 13C signal for en ligands and also for the α-carbons in chxn ligands indicating the presence of two kinds of Pd valence states: Pd(II) and Pd(IV). On the other hand, a sharp singlet line was observed for the α-carbons in the Ni complexes and the Pd monomer complex. These results mean that all Ni atoms in the chain are equivalent and the paramagnetic Ni(III) state is formed. Small chemical shifts observed in the Ni complexes comparable to those in the diamagnetic Pd complexes imply the presence of strong antiferromagnetic interactions between neighboring Ni(III) sites in the chain.