ELECTRONIC, RAMAN AND RESONANCE-RAMAN SPECTROSCOPY OF COPPER(II)-PLATINUM(IV) LINEAR-CHAIN CHLORIDE-BRIDGED COMPLEXES OF 1,2-DIAMINOETHANE

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 Pt(II) --> Pt(IV) intervalence transition of Pt(II)-Pt(IV) domains whose symmetric stretching mode nu-1,nu-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 nu-1'nusym(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 nu-1', 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., perpendicular-to chain direction) on metal ions which are 10.8 angstrom apart.