Triple-ion and quadrupole formation in addition to ion-pair formation from lithium and tributylammonium thiocyanates has been examined by means of conductometry, in several protophobic aprotic solvents: nitrobenzene, benzonitrile, acetonitrile, nitromethane and propylene carbonate. The formation constants of the ion pair (M+ + S C N -e MSCN, K: ; where M + = Li+ or n-Bu,NH+), symmetrical triple ions [2M+ + SCN-e (M+),SCN-, K; ; M + + 2 SCN-=M+(SCN-),, K ! ; Kg = K;] and the quadrupole [(M+),SCN-+ SCN-=(MSCN),, K i ; M + + M+(SCN-),$ (MSCN),, Kz ; Kz = Kg) were evaluated after correction of the activity coefficients of the ions.Effects of the ratio AT/Ao on the conductivities were examined, where AT and A, are the molar conductivities at infinite dilution of the triple ions and simple ions, respectively. A remarkable enhancement of the triple-ion formation from LiSCN was observed in nitromethane: K:' = 5.5 x lo4, Kg' = KZ' = 8.0 x lo7 and AT/Ao = 0.4 (the effects of the ionic atmosphere and viscosity changes are taken into account). At higher salt concentrations, quadrupole formation was observed, which caused the disappearance of the minimum in the A 4 ' 1 2 curve. In contrast, the degree of triple-ion formation from n-Bu,NHSCN was much smaller than that from LiSCN and quadrupole formation was not observed in all the solvents. The formation of (Li+)2SCN-was suggested by spectrophotometry. Both the donor and acceptor numbers of the solvents were concerned with the formation of higher ion aggregates.
