Palladium(II,IV) mixed-valence complexes of 1,2-diaminoethane, 1,3-diaminopropane, and diethylenetriamine: syntheses, electronic, infrared, Raman, and resonance Raman spectra and X-ray studies

Abstract

The syntheses of the neutral, linear-chain mixed-valence complexes [Pd(en)Cl₂][Pd(en)Cl₄], [Pd(en)Br₂][Pd(en)Br₄], [Pd(tn)Br₂][Pd(tn)Br₄], and a mixed-valence complex of empirical formula Pd₂(en)₂Br₃Cl₃, where en = 1,2-diaminoethane and tn = 1,3-diaminopropane, are reported, together with their electronic, infrared, Raman, and resonance Raman spectra. In addition, the synthesis and spectroscopic properties of the first palladium complex of the +1 charge type, [Pd(dien)Br][Pd(dien)Br₃]Br₂, where dien = diethylenetriamine, is reported. The electronic spectra of the complexes are characterised by intense, broad intervalence bands which decrease in wavenumber in the order Cl > Br. The resonance Raman spectra show overtone progressions (v₁v₁) in the axial X–Pd^IV–X symmetric stretching mode (v₁), which lies at ca. 260 cm^–1 for X = Cl and at ca. 145 cm^–1 for X = Br, and combination tones v₁v₁+ v_n, where v_n is the v(Pd–X) equatorial stretching mode, or v₂, v_asym(X–Pd^IV–X), the antisymmetric chain-stretching mode. The excitation profiles of the v₁ and 2v₁ bands of the neutral chain complexes do not reach maxima even with excitation of the lowest available wavenumber (12 510 cm^–1). These complexes appear to be more delocalised than those of the +2 charge type. Powder diffraction data indicate that Pd₂(en)₂Br₃Cl₃ and [Pd(en)Br₂][Pd(en)Br₄] are isostructural and belong to space group Ama2.