The methylamine analogues of Wolffram's red and Reihlen's green: syntheses, infrared, electronic, Raman, and resonance-Raman spectroscopy, and X-ray crystal structures of chain chlorine- and bromine-bridged platinum(II,IV) complexes of methylamine

Abstract

The syntheses and the electronic, i.r., Raman, and resonance-Raman spectra of the mixed-valence chain complexes [Pt(CH3NH2)4][Pt(CH3NH2)4X2][ClO4]4, where X = CI or Br, are reported. The electronic spectra are characterised by intense, broad intervalence bands whose maxima are at 24 100 and 18 200 cm–1, respectively. The i.r. spectra are near superpositions of those of the constituentions. The resonance-Raman spectra are dominated by long overtone progressions in ν1, the symmetric X–PtIV–X stretch, of up to nine members for X = Cl and seven for X = Br. The ω1 and x11 values for each complex are 324.8 ± 0.5 and –0.91 ± 0.07 cm–1, respectively, for X = Cl and 186.3 ± 0.4 and –0.14 ± 0.1 cm–1 for X = Br. The PtIV–X stretching force constants are 2.08 and 1.55 mdyn A–1 for X = Cl and Br, respectively, and the X–PtIV–X interaction constants are 0.074 and 0.057 mdyn A–1, respectively. The excitation profiles for the ν, bands maximise 1500–2800 cm–1 to the red of the PtII→ PtII intervalence band, as determined by transmission measurements. The crystal structures of the two complexes have been determined by single-crystal X-ray methods. In the bromide the structure contains ordered [⋯ PtII(CH3NH2)4⋯ Br–PtII(CH3NH2)4–Br ⋯] chains; the PtIV–Br and PtII–Br distances are 2.468(3) and 3.219(4)A, respectively, and the PtII–Br–PtIV angle is 165.4(3)°. The chloride structure contains an antiparallel disordering of the type of chain found in the bromide. The PtIV–Cl and PtII–Cl distances are 2.334(12) and 3.203(18)A, respectively, and the PtII–Cl–PtIV angle is 170.5(6)°. Both the spectroscopic and the crystallographic evidence indicate that the platinum-ion valences are localised in these complexes.