Toward Elusive Iodoplumbic Acid HPbI3: High-Energy Isochoric Synthesis of Hydronium Forms of the PbI3- Anion at Elevated Temperature and Pressure
High-pressure and -temperature crystallization and X-ray diffraction crystallography have revealed hydronium forms of the proposed but never demonstrated iodoplumbic acid HPbI<sub>3</sub>. Depending on the pressure range, the reaction of PbI2 and aqueous concentrated hydriodic acid under isochoric conditions in a diamond anvil cell (DAC) held between 0.11 and 1.20 GPa produces two hydrated hydronium salts with compositions [H<sub>3</sub>O][PbI<sub>3</sub>].<i>n</i>H<sub>2</sub>O (<i>n</i>=3,4). Comprised of polymeric one-dimensional PbI<sub>3</sub><sup>-</sup> anions, these hydronium salts represent the so far best match for the elusive HPbI<sub>3</sub> progenitor of hybrid lead perovskites. We also reveal a new three-dimensional polymorph of lead iodide (PbI<sub>2</sub>), so far known only as a layered structure.<br>