Salts of Amino Acids with Polar Symmetry Exhibiting a Dimeric Cation of the [A(1)+···A(2)] Type. New Type of Polymorphism

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)+center dot center dot center dot A(2)] type. All have polar symmetry, thus being potential pyroelectrics or ferroelectrics: (L-ProH center dot center dot center dot Sar)BF4 (I), (L-ProH center dot center dot center dot Sar)ClO4 (II), (L-ProH center dot center dot center dot Sar)NO3 (III), (L-ProH center dot center dot center dot Sar)Br (IV), (L-ProH center dot center dot center dot Sar)I (V), (all with space group C2), (f-AlaH center dot center dot center dot DMG)I (VI), (f-AlaH center dot center dot center dot DMG)BF4 (VII), (f-AlaH center dot center dot center dot DMG)NH2SO3 (VIII) and (DMGH center dot center dot center dot Sar)ClO4 (XIII) (all with space group Pna21), (f-AlaH center dot center dot center dot Bet)Br (IX), (f-AlaH center dot center dot center dot Bet)I (X) (both with space group Cc), as well as (SarH center dot center dot center dot DMG)BF4 (XI) and (SarH center dot center dot center dot 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. Pro-tonation in a pair of amino acids may depend on the anion, as in the cases of (SarH center dot center dot center dot Bet)ClO4 and (BetH center dot center dot center dot Sar) NH2SO3 center dot 0.5H2O, (DMGH center dot center dot center dot Bet)ClO4 center dot H2O and (BetH center dot center dot center dot DMG)I center dot H2O or, for the same anion, on the conditions of crystallization, as in the case of (SarH center dot center dot center dot DMG)ClO4 (obtained from aqueous solution) and (DMGH center dot center dot center dot Sar)ClO4 (crystallized from acetic acid). The phases (SarH center dot center dot center dot DMG)(ClO4) (s.g. Pc) and (DMGH center dot center dot center dot 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.