Crystallographic studies on a series of salts of 2,3,7-trihydroxy-9-phenyl-fluorone

2,3,7-Trihydroxy-9-phenyl-fluorone (hereafter H3Z) has been synthesised in its H4Z+, H3Z, H2Z− and Z3− protonation states. X-ray crystal structure determinations have been carried out for (H4Z)(HSO4), H3Z, [EtiPr2NH]H2Z, solvated (PPh4)H2Z and solvated K3Z. In each of these salts the 9-phenyl group adopts a different orientation so as to be involved in intermolecular aromatic interactions. The 3- and 6-phenolic carbon–oxygen bond lengths show that double bond character can be delocalised from the ketone to the deprotonated phenoxide across the conjugated π system of the fluorone.