Two concomitant polymorphs and two isomorphous forms with different chemical compositions, which transform into the same substance upon thermal treatment

Abstract

The organometallic cationic acid [CoIII(η5-C5H4COOH)2]+ (AC) is crystallised from hydrochloric acid solutions in two polymorphic modifications of the salt [CoIII(η5-C5H4COOH)2]Cl·H2O, ACCl·H2Ocube and ACCl·H2Osword. On the other hand, ACCl·H2Osword is isomorphous with the triply-hydrated zwitterion [CoIII(η5-C5H4COOH)(η5-C5H4COO)], ZW·3H2O. ACCl·H2Osword, ACCl·H2Ocube and ZW·3H2O are all converted into the anhydrous form [CoIII(η5-C5H4COOH)(η5-C5H4COO)], ZW, upon thermal treatment. The structural relationship between the ionic and neutral systems and their interconversion have been investigated with a combination of solid-state techniques (single crystal and powder X-ray diffraction, thermogravimetric analysis, mass spectrometry and solid state 13C CP/MAS NMR).