Mixed salts of amino acids: L-histidinium(+) L-histidinium(2+) nitrate-hexafluorosilicate

摘要

Single crystals of the mixed salt L-histidinium(+) L-histidinium(2+) nitrate-hexafluorosilicate have been obtained from aqueous solution and characterized structurally and by infrared and Raman spectroscopy. The title salt crystallizes in the monoclinic system (space group P2 _1, Z = 2). The asymmetric unit contains L-histidinium(+) and L-histidinium(2+) cations as well as nitrate and hexafluorosilicate anions. L-histidinium(+) and L-histidinium(2+) cations form short hydrogen bond with an O?O distance equal to 2.507(2) ?, thus forming a (L-His ~+?L-His ~(2+)) dimeric cation, therefore the formula is correctly given as (L-His ~+?L-His ~(2+))·NO3-·SiF62-. This is the first observation of the (L-His ~+?L-His ~(2+)) dimeric cation. The presence of the OH?O hydrogen bond of the (L-His ~+?L-His ~(2+)) dimeric cation is reflected in the infrared spectrum as a broad absorption band centered at ca. 1300 cm -1 caused by stretching vibration of OH bond.