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)metalate donors exhibit in the solid state IPCT bands the energy of which increases linearly according to the Hush relation with more positive driving 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 typical range of outer-sphere complexes as indicated by the values for the electronic-exchange integral of about 300 and 360 cm(-1) for the nickel, platinum, and palladium compounds, respectively. The total reorganization energy of 32 complexes is 80 kJ/mol and exceeds the previously reported solution value by about 20 kJ/mol. According to the dependence of,the specific electrical conductivity sigma of pressed powder pellets 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, log sigma increases also linearly with decreasing free activation energy (Delta G*) of electron transfer as calculated from the Hush-Marcus model. Contrary to that, neither the driving force nor Delta G* has a significant influence on the conductivity when one of the ion pair components is nonplanar (class II). A hitherto unknown weak absorption band 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-centred transition on the basis of an MO calculation.