DISTANCE DEPENDENCE OF THE EFFECTIVE COUPLING PARAMETERS THROUGH CONJUGATED LIGANDS OF THE POLYENE TYPE

Experimental results on the decay of the effective coupling parameter in mixed valence ruthenium complexes bridged by bipyridylpolyenes are discussed. Absolute values of the couplings are satisfactorily reproduced by extended Hückel calculations. An exponential decrease of the effective coupling is found, with a particularly small exponent, 0.078 Å-1, corresponding to a decrease by a factor of 2 for each 9 Å in the metal-metal distance. The results are also discussed in the frame of a simplified valence bond taking into account the main structural features of the system. It is concluded that, in the present compounds, the transmission of electronic couplings over large distances is limited by the Peierls distortion of the polyene chain. © 1990.