Charge-assisted N–H(+)···O(-) and O–H···O(-) hydrogen bonds control the supramolecular aggregation of ferrocenedicarboxylic acid and bis-amidines

Directional N–H···O and O–H···O hydrogen bonds reinforced by charge assistance in the presence of anion–cation interactions have been used to design and synthesise a whole family of new organic-organometallic supramolecular salts. The compounds [C5H16N4]2+[(η5-C5H4COO)2Fe]2−·2C2H5OH, 1, [C5H16N4]2+{[(η5-C5H4COOH)(η5-C5H4COO)Fe]2}2−, 2, [C7H20N4]2+[(η5-C5H4COO)2Fe]2−·4H2O, 3, [C7H20N4]2+{[(η5-C5H4COOH)(η5-C5H4COO)Fe]2}2−, 4, and [C7H18O2N4]2+[(η5-C5H4COO)2Fe]2− ·4H2O, 5, have been obtained by reacting [(η5-C5H4COOH)2Fe] with the bis-amidines [C5H14N4], [C7H18N4] and [C7H16O2N4]. The self-assembly between singly and doubly deprotonated acids and the protonated cations is controlled by the stoichiometric ratio and by the choice of solvent. The effect of charge assistance on the N–H···O interactions is discussed on the basis of a CSD analysis.