Crystal structures of three β-halolactic acids: hydrogen bonding resulting in differing Z'

Area of Science:

• Crystallography
• Solid-state chemistry
• Organic chemistry

Background:

• Beta-halolactic acids are organic compounds with potential applications in synthesis.
• Understanding their solid-state structures is crucial for predicting reactivity and properties.

Purpose of the Study:

• To determine and compare the crystal structures of beta-chlorolactic acid, beta-bromolactic acid, and beta-iodolactic acid.
• To investigate the intermolecular interactions governing their molecular packing.

Main Methods:

• Single-crystal X-ray diffraction
• Analysis of Hirshfeld surfaces and 2D fingerprint plots
• Energy minimization calculations

Main Results:

• Beta-chlorolactic acid (I) and beta-bromolactic acid (II) were found to be isostructural, each with two molecules in the asymmetric unit (Z'=2).
• Beta-iodolactic acid (III) exhibited a unique structure with one molecule in the asymmetric unit (Z'=1).
• All structures displayed alternating layers of intermolecular hydrogen bonding and halogen-halogen interactions, with differences in hydrogen bond directionality contributing to variations between I and II.

Conclusions:

• The crystal structures of beta-halolactic acids are characterized by distinct packing motifs driven by hydrogen bonding and halogen interactions.
• Isostructurality between beta-chlorolactic and beta-bromolactic acids is attributed to similar hydrogen bonding patterns, while beta-iodolactic acid presents a unique arrangement.
• Hirshfeld surface analysis provides detailed insights into the nature and extent of intermolecular forces within these crystal structures.