Notes. Electronic, Raman and resonance-Raman spectroscopy of copper(II)–platinum(IV) linear-chain chloride-bridged complexes of 1,2-diaminoethane

Abstract

Copper(II)–platinum(IV) linear-chain complexes of the type [Cu_xPt_{1 – x}(en)₂][Pt(en)₂Cl₂][ClO₄]₄(en = 1,2-diaminoethane) have been synthesised where 0.58 < x < 1. The intensely red, highly dichroic needles obtained when x= 0.58 become much paler and lose their dichroism as x→ 1. The intense z-polarised band at 18 000–23 000 cm^–1(single-crystal transmission) for x < 1 is believed to be due to the Pt^II→ Pt^IV intervalence transition of Pt^II–Pt^IV domains whose symmetric stretching mode ν₁,ν_sym(Cl–Pt^IV–Cl) occurs at 313 cm^–1. For the stoichiometric Cu^II–Pt^IV chain complex, the Cu^II→ Pt^IV transition probably lies in the ultraviolet region and the ν′₁,ν_sym(Cl–Pt^IV–Cl) stretching mode occurs at 341 cm^–1. This band displays no resonance enhancement with any excitation lines in the visible or near-ultraviolet region; both this fact, as well as the high value for ν₁′, imply that the stoichiometric material is highly valence localised, as expected for a system consisting of chains in which the unpaired electrons are in d_x²–y² orbitals (i.e., ⊥ chain direction) on metal ions which are 10.8 Å apart.