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–PdIV–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+ vn, where vn is the v(Pd–X) equatorial stretching mode, or v2, vasym(X–PdIV–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.