Salts of amino acids with polar symmetry exhibiting a dimeric cation of the [A(1)+···A(2)] type. New type of polymorphism

Abstract

A new class of amino acids salts containing different amino acids has recently been discovered: the present paper reports on synthesis and crystal structures of thirteen salts with a dimeric cation of the [A(1)+···A(2)] type. All have polar symmetry, thus being potential pyroelectrics or ferroelectrics: (l-ProH···Sar)BF4 (I), (l-ProH···Sar)ClO4 (II), (l-ProH···Sar)NO3 (III), (l-ProH···Sar)Br (IV), (l-ProH···Sar)I (V), (all with space group C2), (β-AlaH···DMG)I (VI), (β-AlaH···DMG)BF4 (VII), (β-AlaH···DMG)NH2SO3 (VIII) and (DMGH···Sar)ClO4 (XIII) (all with space group Pna21), (β-AlaH···Bet)Br (IX), (β-AlaH···Bet)I (X) (both with space group Cc), as well as (SarH···DMG)BF4 (XI) and (SarH···DMG)ClO4 (XII) (both with space group Pc). These compounds except (XIII) are formed by slow evaporation at room temperature from aqueous solutions containing stoichiometric ratios of components. Protonation in a pair of amino acids may depend on the anion, as in the cases of (SarH···Bet)ClO4 and (BetH···Sar)NH2SO3·0.5H2O, (DMGH···Bet)ClO4·H2O and (BetH···DMG)I·H2O or, for the same anion, on the conditions of crystallization, as in the case of (SarH···DMG)ClO4 (obtained from aqueous solution) and (DMGH···Sar)ClO4 (crystallized from acetic acid). The phases (SarH⋅⋅⋅DMG)(ClO4) (s.g. Pc) and (DMGH⋅⋅⋅Sar)(ClO4), (s.g. Pna21) represent a peculiar type of polymorphism, where the difference is evident in the position of the proton in the dimeric cation, too.