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The only possible explanation of the observed efiects is that ionic conductivity in these fused salts is a polyorder process, the ions moving in groups or by means of some chain mechanism, such as a charged hole moving through many ionic diameters with a single activation step. Other mixtures are curretitly under investigation. TABLE
I
I< ELATIVE MOBILITY AND CATION
'rIL4NSPORT NUMBER IS
KN03-LiS03 MIXTURES Total charge passed, -800 coulonibs; T = 360'970O Ratio, K : L i .inode, originally
10 5 3 2 1 0 50 .33
R a t i o K : L i , cathode after elrctrolysi?
Transport no uf cations
10.6 4.95 3.06 2.11 1.06 0,550 ,361 .204 ,106
0 61 .60 . 60 .61 .74 .75 .78
Vol. 83
the plots of charge-transfer absorption frequencies observed with one acceptor v s . those observed with another. TABLE I Donorn
ClCHtCHzCIa mp
CHCXb mp
Benzene 305(sh) (c ) 325 310(sh) Toluene 330 nt-Xylene 34 323 p-Xylene Mesitylene 365 3ad Saphthalene 430 395(sh) 8-Methylnaphthalene 472 Phenanthrene 425(sh) ... Anthracene 530 487 535 ... Pyrene b Tropylium fluoroborate concentration ca. 6 ca. 0.5 M . 10-3 M . Under 275 mp band of tropylium ion. Identical band observed with tropylium perchlorate.
.so
(ii) The wave lengths of the new bands listed in Table I are of the correct order of magnitude for charge-transfer absorptions. Theoretical conIYSTITUTE FOR ATOXICRESEARCH s i d e r a t i o n ~ suggest ~ ~ ~ ~ ~that * hv for charge-transfer AYD DEPARTMEW O F CHEMISTRI' IOWASTATE UNIVERSITY FREDERICK K. DPKE absorption of aromatic hydrocarbon-tropylium ion .$XES, I O K A GEORGEVICTOR complexes should be approximated by the difference between the ionization potential of the RFCEIVED J r ~ w23, 1961 donor and the electron affinity of the acceptor. This is because classical interactions and waveTROPYLIUM ION-AROMATIC HYDROCARBON inechanical exchange forces in the ground and exCHARGE-TRANSFER COMPLEXES cited states can be e ~ p e c t e d 'to ~ make only small .)'21.: contributions to hv. In the LCAOMO first apIn working with solutions oi trop>-liu;ii' per- proximation (neglecting overlap) hv thus turns out chlorate' or tetraAu~,roborate"ill \-arious solvents, to be 1.445p. 1.0636 and 0.859(3 for benzene, we ha\-e abser\-ec-l that adtlitioii o f aromatic hy- naphthalene and anthracene as donors, respecdroc:irbons gives rise to new absorption bands in tively.9 An estimate of an appropriate value for the ultraviolet and visible regions of the spectruni the exchange integral, 6 , may be obtained from the iTable I). It is proposed that the new bands are 275 mp band of tropylium ion, assuming this charge-transfer absorption bands due to charge transition involves excitation of an electron from transfer complexes" of tropyliuiii ion with the the highest energy bonding n-orbital to the lowestvarious hydrocarbons as donors. The general energy anti-bonding one ( h v = 1.6926). On this evidence in favor ( ) i this interpretation may be basis, charge-transfer absorption bands for trosummarized as fol!ows. pyliuni ion complexes with benzene, naphthalene (i) X plot of the ireyueiicirs of the new :tbsorp- and anthracene are predicted a t 322, 438 and 540 tion bands 'F.Y. the frequencies reported for the n i u . respectively. These are in very good general same aromatic hytlrocarboii donors arid trini tro- agrcwiient with observed bands in ethylene chlobenzene.' as acceptor leads to a fair straight linc ride solvent a t 30pj,-180 and 530 mp, respectively.'" with a slope near unity. Similarly. straight liiiei: ( i i i 117th mesitylene concentrations in the 0.1are obtained when the frequencies observed ior 1 ).ciT, .ll range arid a tropyliuni tetrafluoroborate tropylium ion are plotted against those observed cwncentration of 1.3 x 10-3 111 in acetonitrile, with iodine5" or tetracyaiioethylene6 as acceptors. ;I Henesi--Hildebrand plot5 of the observed absorbSince the frequencies of charge-transfer absor1)- ances at '
