I. Nunn et al., CONTROL OF ELECTRICAL-CONDUCTIVITY BY SUPRAMOLECULAR CHARGE-TRANSFER INTERACTIONS IN (DITHIOLENE)METALATE - VIOLOGEN ION-PAIRS, Inorganic chemistry, 33(22), 1994, pp. 5079-5085
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.