Hydrogen-bonded network in biphenyl-4,4'-diphosphonic acid

Area of Science:

• Crystal engineering
• Supramolecular chemistry
• Materials science

Background:

• Understanding molecular self-assembly is crucial for designing novel materials.
• Biphenyl-4,4′-diphosphonic acid (4,4'-bpdp) is a versatile building block for supramolecular structures.
• The interplay of hydrogen bonding and hydrophobic interactions dictates crystal packing.

Purpose of the Study:

• To elucidate the crystal structure of biphenyl-4,4′-diphosphonic acid.
• To investigate the role of different intermolecular interactions in organizing the crystal lattice.
• To understand the structure-property relationships in phosphonic acid-based materials.

Main Methods:

• Single-crystal X-ray diffraction analysis was employed to determine the three-dimensional crystal structure.
• Analysis of hydrogen bonding (O-H...O) and weak interactions (C-H...pi) was performed.
• The molecular symmetry and asymmetric unit content were examined.

Main Results:

• The crystal structure exhibits a unique alternating arrangement of hydrogen-bonded and hydrophobic regions along the a-axis.
• The biphenyl-4,4′-diphosphonic acid molecule lies on an inversion center, with the asymmetric unit containing half of the molecule.
• Strong intermolecular O-H...O hydrogen bonds between phosphonic acid groups are the primary drivers of molecular organization.
• Weak C-H...pi interactions contribute to the stability of the hydrophobic aromatic regions.

Conclusions:

• The crystal structure of biphenyl-4,4′-diphosphonic acid is characterized by a distinct segregation of polar and non-polar regions.
• The interplay between strong hydrogen bonding and weaker C-H...pi interactions governs the overall crystal packing and stability.
• This detailed structural understanding provides insights for the rational design of functional materials based on phosphonic acid derivatives.