CONTROL OF ELECTRICAL-CONDUCTIVITY BY SUPRAMOLECULAR CHARGE-TRANSFER INTERACTIONS IN (DITHIOLENE)METALATE - VIOLOGEN ION-PAIRS

Ion-pair charge-transfer (IPCT) complexes {A(2+)[ML(2)](2-)}, M = Ni, pd, pt, and Cu, between bipyridinium accepters and (dithiolene)metalat e donors exhibit in the solid state IPCT bands the energy of which inc reases linearly according to the Hush relation with more positive driv ing force (Delta G(12)) of electron transfer from [ML(2)](2-) to A(2+) . The electronic interaction between the two redox states is in the ty pical range of outer-sphere complexes as indicated by the values for t he electronic-exchange integral of about 300 and 360 cm(-1) for the ni ckel, platinum, and palladium compounds, respectively. The total reorg anization energy of 32 complexes is 80 kJ/mol and exceeds the previous ly reported solution value by about 20 kJ/mol. According to the depend ence of,the specific electrical conductivity sigma of pressed powder p ellets on Delta G(12) the compounds are divided into two classes. When both donor and acceptor can acquire a planar geometry (class I) it is found that log sigma linearly increases, from 10(-11) to 10(-3) Omega (-1) cm(-1) upon varying Delta G(12) from 0.7 to -0.1 eV. Similarly, l og sigma increases also linearly with decreasing free activation energ y (Delta G) of electron transfer as calculated from the Hush-Marcus m odel. Contrary to that, neither the driving force nor Delta G has a s ignificant influence on the conductivity when one of the ion pair comp onents is nonplanar (class II). A hitherto unknown weak absorption ban d of the [M(dmit)(2)](2-)component, dmit(2-) = 2-thioxo-1,3-dithiol-4, 5-dithioalte, is detected at 1200-1500 nm and assigned to a ligand-cen tred transition on the basis of an MO calculation.