Phenolphthalein and 3',3"-dinitrophenolphthalein

Area of Science:

• Crystallography
• Chemical Physics
• Molecular Structure

Background:

• Phenolphthalein is a widely used pH indicator.
• Understanding the solid-state structure of organic molecules is crucial for predicting their properties.
• Hydrogen bonding plays a significant role in molecular self-assembly and crystal packing.

Purpose of the Study:

• To elucidate the crystal structures of phenolphthalein and 3',3"-dinitrophenolphthalein.
• To analyze and compare the hydrogen bonding networks in both compounds.
• To investigate the influence of nitro group substitution on crystal packing and hydrogen bonding.

Main Methods:

• Single-crystal X-ray diffraction was employed to determine the crystal structures.
• Analysis of intermolecular interactions, including hydrogen bonds (O-H...O and C-H...O), was performed.
• Comparison of crystallographic data (space group, unit cell parameters) between the two compounds.

Main Results:

• Phenolphthalein crystallized in the noncentrosymmetric space group Pna2(1) with two inequivalent molecules, forming extensive chains of hydrogen bonds.
• 3',3"-Dinitrophenolphthalein crystallized in the centrosymmetric space group Pbcn with one molecule per asymmetric unit, exhibiting both chain-like and cyclic hydrogen bonding (dimers).
• Both structures displayed significant C-H...O interactions, attributed to an excess of oxygen acceptor atoms over donors.

Conclusions:

• The crystal structure of phenolphthalein is characterized by non-cyclic hydrogen bonding chains.
• Dinitrophenolphthalein displays a more complex hydrogen bonding network, including cyclic dimers, due to nitro group substitution.
• The study highlights the impact of chemical modification on molecular self-assembly in the solid state.