Syntheses of two novel halomethanetriyltrisphosphonic acids are based on an improved preparation of methanetriyltrisphosphonic acid: pKas for their second acidic dissociations show they are ‘supercharged’ relative to pyrophosphoric acid, PPi, while X-ray crystallographic analysis of fluoromethanetriyltrisphosphonic acid establishes its isosteric character relative to PPi.
