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

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Abstract
Copper(II)–platinum(IV) linear-chain complexes of the type [CuxPt1 – 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 PtII→ PtIV intervalence transition of PtII–PtIV domains whose symmetric stretching mode ν1,νsym(Cl–PtIV–Cl) occurs at 313 cm–1. For the stoichiometric CuII–PtIV chain complex, the CuII→ PtIV transition probably lies in the ultraviolet region and the ν′1,νsym(Cl–PtIV–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 dx2–y2 orbitals (i.e., ⊥ chain direction) on metal ions which are 10.8 Å apart.

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