Crystal and molecular structures of 1:2 crystalline salts of two isomeric double betaines with hydrobromic acid and nitric acid

Abstract

Four 1:2 crystalline salts of the isomeric flexible double betaines 1,4-bis(2-picolyloxyl)benzene- N, N′-diacetate (L 1) and 1,4-bis(3-picolyloxyl)benzene- N, N′-diacetate (L 2) with HBr and HNO 3, [H 2L 1Br 2] 1, [H 2L 1(NO 3) 2] 2, [H 2L 2Br 2] 3 and [H 2L 2(NO 3) 2]·2H 2O 4, have been synthesized and characterized by single-crystal X-ray analysis. They are all hydrogen-bonded networks consolidated by strong intermolecular interactions involving the bromide or nitrate ion, together with π–π stacking between the betaine molecules. The isostructural bromide–nitrate pair of compounds 1 and 2 provide an interesting corollary to the well-known methyl-chloro and benzene–thiophene exchange rules in crystal engineering.