Variable P,T study of iron carbonyl, Fe(CO)5

Iron pentacarbonyl is an iconic molecule with widespread applications in organometallic chemistry. However, its behaviour at non-ambient conditions is poorly known. In a room-temperature study on PEARL, we have determined that the high-pressure phase II differs from the low-temperature ambient-pressure phase we discovered in 2020 using HRPD, contrary to our expectations. Furthermore, we failed to observe the expected phase III. In this work we propose to explore the relationship between the high-pressure phase II (denoted II-HP) and low-temperature phase II (denoted II-LT) by compressing iron pentacarbonyl at 200 K and then attempting to cool close to the temperature of liquid nitrogen. We will also explore pressure-temperature space up to the maximum available load to confirm the non-existence of phase III below room temperature.