Ferrocenecarboxylic anhydride: identification of a new polymorph

Area of Science:

• Organometallic Chemistry
• Crystallography
• Solid-State Chemistry

Background:

• Ferrocenecarboxylic anhydride is an organometallic compound with potential applications in materials science.
• Polymorphism, the ability of a solid material to exist in more than one crystal form, is crucial for understanding material properties.
• Metallocene anhydrides are known for their diverse structural characteristics.

Purpose of the Study:

• To synthesize and characterize a new monoclinic polymorph of ferrocenecarboxylic anhydride.
• To investigate the molecular structure and packing of the new polymorph.
• To explore the structural diversity within metallocene anhydrides.

Main Methods:

• Single-crystal X-ray diffraction was used to determine the crystal structure.
• Analysis of molecular arrangements and intermolecular interactions.
• Comparison with known polymorphs and related compounds.

Main Results:

• A new monoclinic polymorph of ferrocenecarboxylic anhydride, [Fe2(C5H5)2(C12H8O3)], was successfully obtained.
• The asymmetric unit contains three molecules, with two nearly identical and a third exhibiting an unusual ferrocene-ferrocene pseudo-torsion angle of 146.2°.
• A network of weak intermolecular hydrogen bonds was identified, contributing to the crystal structure.

Conclusions:

• The discovery of this new polymorph highlights the rich structural chemistry of ferrocenecarboxylic anhydride.
• The unusual molecular conformation in one of the independent molecules provides new insights into metallocene anhydride structures.
• The presence of hydrogen bonding influences the crystal packing and stability of the new form.