Unusual Complexes of P(CH)₃ with FH, ClH, and ClF

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Interactions

Background:

• Phosphatetrahedrane (P(CH3)3) is a unique phosphorus-containing molecule.
• Understanding non-covalent interactions is crucial in chemistry.
• Previous studies have not fully characterized complexes of P(CH3)3 with acidic molecules.

Purpose of the Study:

• To determine the structures and binding energies of complexes formed between phosphatetrahedrane and hydrogen fluoride (HF), hydrogen chloride (HCl), and chlorine monofluoride (ClF).
• To investigate the nature of stabilizing interactions (hydrogen bonds vs. halogen bonds) and their impact on complex stability.
• To analyze the energetic components contributing to complex stability using Symmetry Adapted Perturbation Theory (SAPT).

Main Methods:

• Ab initio MP2/aug'-cc-pVTZ calculations were employed to model the molecular complexes.
• Potential energy surfaces were explored to identify different isomeric structures (A, B, C, D).
• Symmetry Adapted Perturbation Theory (SAPT) was used to dissect the binding energy components.
• Equation of Motion Coupled Cluster Singles and Doubles (EOM-CCSD) was utilized to calculate intermolecular coupling constants.

Main Results:

• Four types of complexes (A, B, C, D) were identified, differing in interaction sites on phosphatetrahedrane.
• Complexes A and B are stabilized by hydrogen bonds (with HF, HCl) or halogen bonds (with ClF).
• Binding energies follow the order A > B > C > D, with electrostatic interactions dominating A and B, and dispersion interactions dominating C and D.
• Isomer A exhibits higher conversion barriers than isomer B.
• Intermolecular coupling constants (J(X-P)) show distinct patterns across isomers, with significant changes in the halogen-bonded complex A.

Conclusions:

• The study provides a comprehensive understanding of the structural and energetic landscape of phosphatetrahedrane complexes with acidic molecules.
• The type of interaction (hydrogen vs. halogen bonding) and the binding site significantly influence complex stability and properties.
• Computational methods effectively elucidate the nuances of non-covalent interactions in these systems.