Mixed salts of amino acids: On the vibrational spectra of mixed salts containing a l-lysinium(+)⋯l-lysinium(2+) dimeric cation

The crystal structure of the mixed salt l-lysinium(+)⋯l-lysinium(2+) dichloride-tetrafluoroborate ((L-Lys+⋯l-Lys2+)·2Cl−·BF4-) has been determined. The crystal is orthorhombic (space group P212121) and comprises dimeric (l-Lys+⋯l-Lys2+) cations in fully extended configuration, as well as Cl− and BF4- anions. The vibrational spectra of (l-Lys+⋯l-Lys2+)·2Cl−·BF4-, as well as those of the previously reported mixed salts (l-Lys+⋯l-Lys2+)·2Cl−·ClO4- and (l-Lys+⋯l-Lys2+)·2Cl−·NO3- have been recorded and were found to be characterized by the presence of a band near 1680 cm−1, characteristic for the dimeric cation (l-Lys+⋯l-Lys2+). Previously published spectra ascribed to (l-Lys+⋯l-Lys2+)·2Cl−·NO3-, containing a band near 1734 cm−1, probably relate to l-Lys2+·Cl−·NO3- crystals.