C. Handrosch et al., Charge-transfer complexes of metal dithiolenes XXVI Azobipyridinium dications and radical monocations as accepters, EUR J INORG, (8), 1999, pp. 1259-1269
Combination of the planar redox-active ions [ML2](2-) (L = mnt(2-) = maleon
itrile-1,2- dithiolate; M = Ni (1), Pd (2), Pt (3); dmit(2-) = 2-thioxo-1,3
-dithiol-4,5-dithiolate: M = Ni (4), Pd (5) and trans-4,4'-azobis(1-methyl-
pyridinium), (a(2+)) affords 1:1 ion pairs exhibiting partial and complete
electron transfer as evidenced by UV-Vis and EPR spectra, Replacement of pl
anar a(2+) by a non-planar dipyridinium ketone b(2+) leads to the complexes
1b and 4b, 1a, 2a, and 3a are predominantly composed of dications and dian
ions while 4a, 5a, and 4b are rare examples of ion pairs consisting of two
radical ions. Single crystal X-ray structural analyses was performed on 4a,
a(PF6)(2) and a(MeSO4)(2) while the structure of 1a was resolved by powder
X-ray diffractometry. The latter consists of mixed stacks of planar dianio
ns and dications forming a slipped arrangement with the centers of the two
ions displaced relative to each other by 250 pm. The short interplanar dist
ances of 340 pm are in agreement with the presence of a weak charge-transfe
r interaction as indicated by the corresponding absorption band at about 14
00 nm, A mean reorganization energy of 0.85 +/- 0.04 eV is calculated from
the Hush equation for complexes 1a, 2a, and 3a. No ion pair charge-transfer
band is observable for 4a, 5a, and 4b. Surprisingly, in the solid state st
ructure of 4a the [Ni(dmit)2](-) monoanions do not form segregated columns
as found in the many ion pairs with redox inert counterions, but prefer a m
ixed stack arrangement as observed also for 1a. The specific electrical con
ductivity of pressed powder pellets of complexes exhibiting a charge-transf
er band is in the range of 2 x 10(-7) to 1 x 10(-5) Ohm(-1)cm(-1), increasi
ng with increasing driving force of electron transfer in accordance with pr
evious results. Different to that, the conductivity of the other complexes
does not depend on driving force and is much higher (2 x 10(-4) to 4 x 10(-
4) Ohm(-1)cm(-1)).