Extremely high concentrated solutions of lithium perchlorate in formamide and acetonitrile equimolar mixture were investigated by spectroscopic and conductimetric techniques. The spectral changes observed in the characteristic bands of the solvents, the appearance of the band at 939cm−1 and the slight increase of conductivity in all solutions were interpreted in terms of a solvent separated ion pairs model. In fact, the mixture of solvents with considerable differences in the donor–acceptor characters allows to prepare electrolytic solutions where the contact ion pairs formation seems uncertain.