X-Ray Photoelectron Spectra and Electrical Conductivities of One-dimensional Halogen-bridged Pd(II)–Pt(IV) and Ni(II)–Pt(IV) Mixed-valence Complexes

Abstract

Abstract The X-ray photoelectron spectra have been measured for the one-dimensional halogen-bridged metal-alternated mixed-valence complexes, [PdII(en)2][PtIVX2(en)2](ClO4)4 (X=Cl, Br, and I) and [NiII(en)2][PtIVX2(en)2](ClO4)4(X=Cl and Br), along with their parent complexes, [Pd(en)2]Cl2, Ni(en)2Cl2, and [PtCl2(en)2]Cl2. As the bridging halogen changes from Cl to I, the binding energies of the Pt(IV)4f levels become lower while those of M(II) (M=Pd and Ni) levels become higher, each gradually approaching to the M(III) binding energies (M=Pt, Pd, or Ni), respectively. Comparing the binding energies of the Pt(IV)4f levels in these hetero-metal mixedvalence complexes with those previously reported for the homo-metal halogen-bridged Pt(II)–Pt(IV) mixedvalence complexes having the same bridging halogens, the reductive trend of the oxidation states of Pt(IV) is found to be significantly suppressed by the metal alternation. In accord with this result, the activation energies obtained from the electrical conductivities are fairly larger than those of the homo-metal Pt(II)–Pt(IV) mixed-valence complexes. Their magnitudes are in the order of PdII–PtIV>NiII–PtIV>PtII–PtIV, suggesting that the electron–electron repulsion energy on M(II) ions plays an important role in mixed-valence states.